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tkImgPhoto.c

/*
 * tkImgPhoto.c --
 *
 *    Implements images of type "photo" for Tk.  Photo images are
 *    stored in full color (24 bits per pixel) and displayed using
 *    dithering if necessary.
 *
 * Copyright (c) 1994 The Australian National University.
 * Copyright (c) 1994-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tkImgPhoto.c,v 1.3 1998/09/30 19:01:20 rjohnson Exp $
 */

#include "tkInt.h"
#include "tkPort.h"
#include "tclMath.h"
#include <ctype.h>

/*
 * Declaration for internal Xlib function used here:
 */

extern _XInitImageFuncPtrs _ANSI_ARGS_((XImage *image));

/*
 * A signed 8-bit integral type.  If chars are unsigned and the compiler
 * isn't an ANSI one, then we have to use short instead (which wastes
 * space) to get signed behavior.
 */

#if defined(__STDC__) || defined(_AIX)
    typedef signed char schar;
#else
#   ifndef __CHAR_UNSIGNED__
      typedef char schar;
#   else
      typedef short schar;
#   endif
#endif

/*
 * An unsigned 32-bit integral type, used for pixel values.
 * We use int rather than long here to accommodate those systems
 * where longs are 64 bits.
 */

typedef unsigned int pixel;

/*
 * The maximum number of pixels to transmit to the server in a
 * single XPutImage call.
 */

#define MAX_PIXELS 65536

/*
 * The set of colors required to display a photo image in a window depends on:
 *    - the visual used by the window
 *    - the palette, which specifies how many levels of each primary
 *      color to use, and
 *    - the gamma value for the image.
 *
 * Pixel values allocated for specific colors are valid only for the
 * colormap in which they were allocated.  Sets of pixel values
 * allocated for displaying photos are re-used in other windows if
 * possible, that is, if the display, colormap, palette and gamma
 * values match.  A hash table is used to locate these sets of pixel
 * values, using the following data structure as key:
 */

typedef struct {
    Display *display;         /* Qualifies the colormap resource ID */
    Colormap colormap;        /* Colormap that the windows are using. */
    double gamma;       /* Gamma exponent value for images. */
    Tk_Uid palette;           /* Specifies how many shades of each primary
                         * we want to allocate. */
} ColorTableId;

/*
 * For a particular (display, colormap, palette, gamma) combination,
 * a data structure of the following type is used to store the allocated
 * pixel values and other information:
 */

typedef struct ColorTable {
    ColorTableId id;          /* Information used in selecting this
                         * color table. */
    int     flags;                  /* See below. */
    int     refCount;         /* Number of instances using this map. */
    int liveRefCount;         /* Number of instances which are actually
                         * in use, using this map. */
    int     numColors;        /* Number of colors allocated for this map. */

    XVisualInfo   visualInfo; /* Information about the visual for windows
                         * using this color table. */

    pixel redValues[256];     /* Maps 8-bit values of red intensity
                         * to a pixel value or index in pixelMap. */
    pixel greenValues[256];   /* Ditto for green intensity */
    pixel blueValues[256];    /* Ditto for blue intensity */
    unsigned long *pixelMap;  /* Actual pixel values allocated. */

    unsigned char colorQuant[3][256];
                        /* Maps 8-bit intensities to quantized
                         * intensities.  The first index is 0 for
                         * red, 1 for green, 2 for blue. */
} ColorTable;

/*
 * Bit definitions for the flags field of a ColorTable.
 * BLACK_AND_WHITE:           1 means only black and white colors are
 *                      available.
 * COLOR_WINDOW:        1 means a full 3-D color cube has been
 *                      allocated.
 * DISPOSE_PENDING:           1 means a call to DisposeColorTable has
 *                      been scheduled as an idle handler, but it
 *                      hasn't been invoked yet.
 * MAP_COLORS:                1 means pixel values should be mapped
 *                      through pixelMap.
 */

#define BLACK_AND_WHITE       1
#define COLOR_WINDOW          2
#define DISPOSE_PENDING       4
#define MAP_COLORS            8

/*
 * Definition of the data associated with each photo image master.
 */

typedef struct PhotoMaster {
    Tk_ImageMaster tkMaster;  /* Tk's token for image master.  NULL means
                         * the image is being deleted. */
    Tcl_Interp *interp;       /* Interpreter associated with the
                         * application using this image. */
    Tcl_Command imageCmd;     /* Token for image command (used to delete
                         * it when the image goes away).  NULL means
                         * the image command has already been
                         * deleted. */
    int     flags;                  /* Sundry flags, defined below. */
    int     width, height;          /* Dimensions of image. */
    int userWidth, userHeight;      /* User-declared image dimensions. */
    Tk_Uid palette;           /* User-specified default palette for
                         * instances of this image. */
    double gamma;       /* Display gamma value to correct for. */
    char *fileString;         /* Name of file to read into image. */
    char *dataString;         /* String value to use as contents of image. */
    char *format;       /* User-specified format of data in image
                         * file or string value. */
    unsigned char *pix24;     /* Local storage for 24-bit image. */
    int ditherX, ditherY;     /* Location of first incorrectly
                         * dithered pixel in image. */
    TkRegion validRegion;     /* Tk region indicating which parts of
                         * the image have valid image data. */
    struct PhotoInstance *instancePtr;
                        /* First in the list of instances
                         * associated with this master. */
} PhotoMaster;

/*
 * Bit definitions for the flags field of a PhotoMaster.
 * COLOR_IMAGE:               1 means that the image has different color
 *                      components.
 * IMAGE_CHANGED:       1 means that the instances of this image
 *                      need to be redithered.
 */

#define COLOR_IMAGE           1
#define IMAGE_CHANGED         2

/*
 * The following data structure represents all of the instances of
 * a photo image in windows on a given screen that are using the
 * same colormap.
 */

typedef struct PhotoInstance {
    PhotoMaster *masterPtr;   /* Pointer to master for image. */
    Display *display;         /* Display for windows using this instance. */
    Colormap colormap;        /* The image may only be used in windows with
                         * this particular colormap. */
    struct PhotoInstance *nextPtr;
                        /* Pointer to the next instance in the list
                         * of instances associated with this master. */
    int refCount;       /* Number of instances using this structure. */
    Tk_Uid palette;           /* Palette for these particular instances. */
    double gamma;       /* Gamma value for these instances. */
    Tk_Uid defaultPalette;    /* Default palette to use if a palette
                         * is not specified for the master. */
    ColorTable *colorTablePtr;      /* Pointer to information about colors
                         * allocated for image display in windows
                         * like this one. */
    Pixmap pixels;            /* X pixmap containing dithered image. */
    int width, height;        /* Dimensions of the pixmap. */
    schar *error;       /* Error image, used in dithering. */
    XImage *imagePtr;         /* Image structure for converted pixels. */
    XVisualInfo visualInfo;   /* Information about the visual that these
                         * windows are using. */
    GC gc;              /* Graphics context for writing images
                         * to the pixmap. */
} PhotoInstance;

/*
 * The following data structure is used to return information
 * from ParseSubcommandOptions:
 */

struct SubcommandOptions {
    int options;        /* Individual bits indicate which
                         * options were specified - see below. */
    char *name;               /* Name specified without an option. */
    int fromX, fromY;         /* Values specified for -from option. */
    int fromX2, fromY2;       /* Second coordinate pair for -from option. */
    int toX, toY;       /* Values specified for -to option. */
    int toX2, toY2;           /* Second coordinate pair for -to option. */
    int zoomX, zoomY;         /* Values specified for -zoom option. */
    int subsampleX, subsampleY;     /* Values specified for -subsample option. */
    char *format;       /* Value specified for -format option. */
};

/*
 * Bit definitions for use with ParseSubcommandOptions:
 * Each bit is set in the allowedOptions parameter on a call to
 * ParseSubcommandOptions if that option is allowed for the current
 * photo image subcommand.  On return, the bit is set in the options
 * field of the SubcommandOptions structure if that option was specified.
 *
 * OPT_FORMAT:                Set if -format option allowed/specified.
 * OPT_FROM:                  Set if -from option allowed/specified.
 * OPT_SHRINK:                Set if -shrink option allowed/specified.
 * OPT_SUBSAMPLE:       Set if -subsample option allowed/spec'd.
 * OPT_TO:              Set if -to option allowed/specified.
 * OPT_ZOOM:                  Set if -zoom option allowed/specified.
 */

#define OPT_FORMAT      1
#define OPT_FROM  2
#define OPT_SHRINK      4
#define OPT_SUBSAMPLE   8
#define OPT_TO          0x10
#define OPT_ZOOM  0x20

/*
 * List of option names.  The order here must match the order of
 * declarations of the OPT_* constants above.
 */

static char *optionNames[] = {
    "-format",
    "-from",
    "-shrink",
    "-subsample",
    "-to",
    "-zoom",
    (char *) NULL
};

/*
 * The type record for photo images:
 */

static int        ImgPhotoCreate _ANSI_ARGS_((Tcl_Interp *interp,
                      char *name, int argc, char **argv,
                      Tk_ImageType *typePtr, Tk_ImageMaster master,
                      ClientData *clientDataPtr));
static ClientData ImgPhotoGet _ANSI_ARGS_((Tk_Window tkwin,
                      ClientData clientData));
static void       ImgPhotoDisplay _ANSI_ARGS_((ClientData clientData,
                      Display *display, Drawable drawable,
                      int imageX, int imageY, int width, int height,
                      int drawableX, int drawableY));
static void       ImgPhotoFree _ANSI_ARGS_((ClientData clientData,
                      Display *display));
static void       ImgPhotoDelete _ANSI_ARGS_((ClientData clientData));

Tk_ImageType tkPhotoImageType = {
    "photo",                  /* name */
    ImgPhotoCreate,           /* createProc */
    ImgPhotoGet,        /* getProc */
    ImgPhotoDisplay,          /* displayProc */
    ImgPhotoFree,       /* freeProc */
    ImgPhotoDelete,           /* deleteProc */
    (Tk_ImageType *) NULL     /* nextPtr */
};

/*
 * Default configuration
 */

#define DEF_PHOTO_GAMMA       "1"
#define DEF_PHOTO_HEIGHT      "0"
#define DEF_PHOTO_PALETTE     ""
#define DEF_PHOTO_WIDTH       "0"

/*
 * Information used for parsing configuration specifications:
 */
static Tk_ConfigSpec configSpecs[] = {
    {TK_CONFIG_STRING, "-data", (char *) NULL, (char *) NULL,
       (char *) NULL, Tk_Offset(PhotoMaster, dataString), TK_CONFIG_NULL_OK},
    {TK_CONFIG_STRING, "-format", (char *) NULL, (char *) NULL,
       (char *) NULL, Tk_Offset(PhotoMaster, format), TK_CONFIG_NULL_OK},
    {TK_CONFIG_STRING, "-file", (char *) NULL, (char *) NULL,
       (char *) NULL, Tk_Offset(PhotoMaster, fileString), TK_CONFIG_NULL_OK},
    {TK_CONFIG_DOUBLE, "-gamma", (char *) NULL, (char *) NULL,
       DEF_PHOTO_GAMMA, Tk_Offset(PhotoMaster, gamma), 0},
    {TK_CONFIG_INT, "-height", (char *) NULL, (char *) NULL,
       DEF_PHOTO_HEIGHT, Tk_Offset(PhotoMaster, userHeight), 0},
    {TK_CONFIG_UID, "-palette", (char *) NULL, (char *) NULL,
       DEF_PHOTO_PALETTE, Tk_Offset(PhotoMaster, palette), 0},
    {TK_CONFIG_INT, "-width", (char *) NULL, (char *) NULL,
       DEF_PHOTO_WIDTH, Tk_Offset(PhotoMaster, userWidth), 0},
    {TK_CONFIG_END, (char *) NULL, (char *) NULL, (char *) NULL,
       (char *) NULL, 0, 0}
};

/*
 * Hash table used to hash from (display, colormap, palette, gamma)
 * to ColorTable address.
 */

static Tcl_HashTable imgPhotoColorHash;
static int imgPhotoColorHashInitialized;
#define N_COLOR_HASH    (sizeof(ColorTableId) / sizeof(int))

/*
 * Pointer to the first in the list of known photo image formats.
 */

static Tk_PhotoImageFormat *formatList = NULL;

/*
 * Forward declarations
 */

static int        ImgPhotoCmd _ANSI_ARGS_((ClientData clientData,
                      Tcl_Interp *interp, int argc, char **argv));
static int        ParseSubcommandOptions _ANSI_ARGS_((
                      struct SubcommandOptions *optPtr,
                      Tcl_Interp *interp, int allowedOptions,
                      int *indexPtr, int argc, char **argv));
static void       ImgPhotoCmdDeletedProc _ANSI_ARGS_((
                      ClientData clientData));
static int        ImgPhotoConfigureMaster _ANSI_ARGS_((
                      Tcl_Interp *interp, PhotoMaster *masterPtr,
                      int argc, char **argv, int flags));
static void       ImgPhotoConfigureInstance _ANSI_ARGS_((
                      PhotoInstance *instancePtr));
static void       ImgPhotoSetSize _ANSI_ARGS_((PhotoMaster *masterPtr,
                      int width, int height));
static void       ImgPhotoInstanceSetSize _ANSI_ARGS_((
                      PhotoInstance *instancePtr));
static int        IsValidPalette _ANSI_ARGS_((PhotoInstance *instancePtr,
                      char *palette));
static int        CountBits _ANSI_ARGS_((pixel mask));
static void       GetColorTable _ANSI_ARGS_((PhotoInstance *instancePtr));
static void       FreeColorTable _ANSI_ARGS_((ColorTable *colorPtr));
static void       AllocateColors _ANSI_ARGS_((ColorTable *colorPtr));
static void       DisposeColorTable _ANSI_ARGS_((ClientData clientData));
static void       DisposeInstance _ANSI_ARGS_((ClientData clientData));
static int        ReclaimColors _ANSI_ARGS_((ColorTableId *id,
                      int numColors));
static int        MatchFileFormat _ANSI_ARGS_((Tcl_Interp *interp,
                      Tcl_Channel chan, char *fileName,
                      char *formatString,
                      Tk_PhotoImageFormat **imageFormatPtr,
                      int *widthPtr, int *heightPtr));
static int        MatchStringFormat _ANSI_ARGS_((Tcl_Interp *interp,
                      char *string, char *formatString,
                      Tk_PhotoImageFormat **imageFormatPtr,
                      int *widthPtr, int *heightPtr));
static void       Dither _ANSI_ARGS_((PhotoMaster *masterPtr,
                      int x, int y, int width, int height));
static void       DitherInstance _ANSI_ARGS_((PhotoInstance *instancePtr,
                      int x, int y, int width, int height));

#undef MIN
#define MIN(a, b) ((a) < (b)? (a): (b))
#undef MAX
#define MAX(a, b) ((a) > (b)? (a): (b))

/*
 *----------------------------------------------------------------------
 *
 * Tk_CreatePhotoImageFormat --
 *
 *    This procedure is invoked by an image file handler to register
 *    a new photo image format and the procedures that handle the
 *    new format.  The procedure is typically invoked during
 *    Tcl_AppInit.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The new image file format is entered into a table used in the
 *    photo image "read" and "write" subcommands.
 *
 *----------------------------------------------------------------------
 */

void
Tk_CreatePhotoImageFormat(formatPtr)
    Tk_PhotoImageFormat *formatPtr;
                        /* Structure describing the format.  All of
                         * the fields except "nextPtr" must be filled
                         * in by caller.  Must not have been passed
                         * to Tk_CreatePhotoImageFormat previously. */
{
    Tk_PhotoImageFormat *copyPtr;

    copyPtr = (Tk_PhotoImageFormat *) ckalloc(sizeof(Tk_PhotoImageFormat));
    *copyPtr = *formatPtr;
    copyPtr->name = (char *) ckalloc((unsigned) (strlen(formatPtr->name) + 1));
    strcpy(copyPtr->name, formatPtr->name);
    copyPtr->nextPtr = formatList;
    formatList = copyPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoCreate --
 *
 *    This procedure is called by the Tk image code to create
 *    a new photo image.
 *
 * Results:
 *    A standard Tcl result.
 *
 * Side effects:
 *    The data structure for a new photo image is allocated and
 *    initialized.
 *
 *----------------------------------------------------------------------
 */

static int
ImgPhotoCreate(interp, name, argc, argv, typePtr, master, clientDataPtr)
    Tcl_Interp *interp;       /* Interpreter for application containing
                         * image. */
    char *name;               /* Name to use for image. */
    int argc;                 /* Number of arguments. */
    char **argv;        /* Argument strings for options (doesn't
                         * include image name or type). */
    Tk_ImageType *typePtr;    /* Pointer to our type record (not used). */
    Tk_ImageMaster master;    /* Token for image, to be used by us in
                         * later callbacks. */
    ClientData *clientDataPtr;      /* Store manager's token for image here;
                         * it will be returned in later callbacks. */
{
    PhotoMaster *masterPtr;

    /*
     * Allocate and initialize the photo image master record.
     */

    masterPtr = (PhotoMaster *) ckalloc(sizeof(PhotoMaster));
    memset((void *) masterPtr, 0, sizeof(PhotoMaster));
    masterPtr->tkMaster = master;
    masterPtr->interp = interp;
    masterPtr->imageCmd = Tcl_CreateCommand(interp, name, ImgPhotoCmd,
          (ClientData) masterPtr, ImgPhotoCmdDeletedProc);
    masterPtr->palette = NULL;
    masterPtr->pix24 = NULL;
    masterPtr->instancePtr = NULL;
    masterPtr->validRegion = TkCreateRegion();

    /*
     * Process configuration options given in the image create command.
     */

    if (ImgPhotoConfigureMaster(interp, masterPtr, argc, argv, 0) != TCL_OK) {
      ImgPhotoDelete((ClientData) masterPtr);
      return TCL_ERROR;
    }

    *clientDataPtr = (ClientData) masterPtr;
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoCmd --
 *
 *    This procedure is invoked to process the Tcl command that
 *    corresponds to a photo image.  See the user documentation
 *    for details on what it does.
 *
 * Results:
 *    A standard Tcl result.
 *
 * Side effects:
 *    See the user documentation.
 *
 *----------------------------------------------------------------------
 */

static int
ImgPhotoCmd(clientData, interp, argc, argv)
    ClientData clientData;    /* Information about photo master. */
    Tcl_Interp *interp;       /* Current interpreter. */
    int argc;                 /* Number of arguments. */
    char **argv;        /* Argument strings. */
{
    PhotoMaster *masterPtr = (PhotoMaster *) clientData;
    int c, result, index;
    int x, y, width, height;
    int dataWidth, dataHeight;
    struct SubcommandOptions options;
    int listArgc;
    char **listArgv;
    char **srcArgv;
    unsigned char *pixelPtr;
    Tk_PhotoImageBlock block;
    Tk_Window tkwin;
    char string[16];
    XColor color;
    Tk_PhotoImageFormat *imageFormat;
    int imageWidth, imageHeight;
    int matched;
    Tcl_Channel chan;
    Tk_PhotoHandle srcHandle;
    size_t length;

    if (argc < 2) {
      Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
            " option ?arg arg ...?\"", (char *) NULL);
      return TCL_ERROR;
    }
    c = argv[1][0];
    length = strlen(argv[1]);

    if ((c == 'b') && (strncmp(argv[1], "blank", length) == 0)) {
      /*
       * photo blank command - just call Tk_PhotoBlank.
       */

      if (argc == 2) {
          Tk_PhotoBlank(masterPtr);
      } else {
          Tcl_AppendResult(interp, "wrong # args: should be \"",
                argv[0], " blank\"", (char *) NULL);
          return TCL_ERROR;
      }
    } else if ((c == 'c') && (length >= 2)
          && (strncmp(argv[1], "cget", length) == 0)) {
      if (argc != 3) {
          Tcl_AppendResult(interp, "wrong # args: should be \"",
                argv[0], " cget option\"",
                (char *) NULL);
          return TCL_ERROR;
      }
      Tk_ConfigureValue(interp, Tk_MainWindow(interp), configSpecs,
            (char *) masterPtr, argv[2], 0);
    } else if ((c == 'c') && (length >= 3)
          && (strncmp(argv[1], "configure", length) == 0)) {
      /*
       * photo configure command - handle this in the standard way.
       */

      if (argc == 2) {
          return Tk_ConfigureInfo(interp, Tk_MainWindow(interp),
                configSpecs, (char *) masterPtr, (char *) NULL, 0);
      }
      if (argc == 3) {
          return Tk_ConfigureInfo(interp, Tk_MainWindow(interp),
                configSpecs, (char *) masterPtr, argv[2], 0);
      }
      return ImgPhotoConfigureMaster(interp, masterPtr, argc-2, argv+2,
            TK_CONFIG_ARGV_ONLY);
    } else if ((c == 'c') && (length >= 3)
          && (strncmp(argv[1], "copy", length) == 0)) {
      /*
       * photo copy command - first parse options.
       */

      index = 2;
      memset((VOID *) &options, 0, sizeof(options));
      options.zoomX = options.zoomY = 1;
      options.subsampleX = options.subsampleY = 1;
      options.name = NULL;
      if (ParseSubcommandOptions(&options, interp,
            OPT_FROM | OPT_TO | OPT_ZOOM | OPT_SUBSAMPLE | OPT_SHRINK,
            &index, argc, argv) != TCL_OK) {
          return TCL_ERROR;
      }
      if (options.name == NULL || index < argc) {
          Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
                " copy source-image ?-from x1 y1 x2 y2?",
                " ?-to x1 y1 x2 y2? ?-zoom x y? ?-subsample x y?",
                "\"", (char *) NULL);
          return TCL_ERROR;
      }

      /*
       * Look for the source image and get a pointer to its image data.
       * Check the values given for the -from option.
       */

      if ((srcHandle = Tk_FindPhoto(interp, options.name)) == NULL) {
          Tcl_AppendResult(interp, "image \"", argv[2], "\" doesn't",
                " exist or is not a photo image", (char *) NULL);
          return TCL_ERROR;
      }
      Tk_PhotoGetImage(srcHandle, &block);
      if ((options.fromX2 > block.width) || (options.fromY2 > block.height)
            || (options.fromX2 > block.width)
            || (options.fromY2 > block.height)) {
          Tcl_AppendResult(interp, "coordinates for -from option extend ",
                "outside source image", (char *) NULL);
          return TCL_ERROR;
      }

      /*
       * Fill in default values for unspecified parameters.
       */

      if (((options.options & OPT_FROM) == 0) || (options.fromX2 < 0)) {
          options.fromX2 = block.width;
          options.fromY2 = block.height;
      }
      if (((options.options & OPT_TO) == 0) || (options.toX2 < 0)) {
          width = options.fromX2 - options.fromX;
          if (options.subsampleX > 0) {
            width = (width + options.subsampleX - 1) / options.subsampleX;
          } else if (options.subsampleX == 0) {
            width = 0;
          } else {
            width = (width - options.subsampleX - 1) / -options.subsampleX;
          }
          options.toX2 = options.toX + width * options.zoomX;

          height = options.fromY2 - options.fromY;
          if (options.subsampleY > 0) {
            height = (height + options.subsampleY - 1)
                  / options.subsampleY;
          } else if (options.subsampleY == 0) {
            height = 0;
          } else {
            height = (height - options.subsampleY - 1)
                  / -options.subsampleY;
          }
          options.toY2 = options.toY + height * options.zoomY;
      }

      /*
       * Set the destination image size if the -shrink option was specified.
       */

      if (options.options & OPT_SHRINK) {
          ImgPhotoSetSize(masterPtr, options.toX2, options.toY2);
      }

      /*
       * Copy the image data over using Tk_PhotoPutZoomedBlock.
       */

      block.pixelPtr += options.fromX * block.pixelSize
          + options.fromY * block.pitch;
      block.width = options.fromX2 - options.fromX;
      block.height = options.fromY2 - options.fromY;
      Tk_PhotoPutZoomedBlock((Tk_PhotoHandle) masterPtr, &block,
            options.toX, options.toY, options.toX2 - options.toX,
            options.toY2 - options.toY, options.zoomX, options.zoomY,
            options.subsampleX, options.subsampleY);

    } else if ((c == 'g') && (strncmp(argv[1], "get", length) == 0)) {
      /*
       * photo get command - first parse and check parameters.
       */

      if (argc != 4) {
          Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
                " get x y\"", (char *) NULL);
          return TCL_ERROR;
      }
      if ((Tcl_GetInt(interp, argv[2], &x) != TCL_OK)
            || (Tcl_GetInt(interp, argv[3], &y) != TCL_OK)) {
          return TCL_ERROR;
      }
      if ((x < 0) || (x >= masterPtr->width)
            || (y < 0) || (y >= masterPtr->height)) {
          Tcl_AppendResult(interp, argv[0], " get: ",
                "coordinates out of range", (char *) NULL);
          return TCL_ERROR;
      }

      /*
       * Extract the value of the desired pixel and format it as a string.
       */

      pixelPtr = masterPtr->pix24 + (y * masterPtr->width + x) * 3;
      sprintf(string, "%d %d %d", pixelPtr[0], pixelPtr[1],
            pixelPtr[2]);
      Tcl_AppendResult(interp, string, (char *) NULL);
    } else if ((c == 'p') && (strncmp(argv[1], "put", length) == 0)) {
      /*
       * photo put command - first parse the options and colors specified.
       */

      index = 2;
      memset((VOID *) &options, 0, sizeof(options));
      options.name = NULL;
      if (ParseSubcommandOptions(&options, interp, OPT_TO,
             &index, argc, argv) != TCL_OK) {
          return TCL_ERROR;
      }
      if ((options.name == NULL) || (index < argc)) {
          Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
                 " put {{colors...}...} ?-to x1 y1 x2 y2?\"",
                 (char *) NULL);
          return TCL_ERROR;
      }
      if (Tcl_SplitList(interp, options.name, &dataHeight, &srcArgv)
            != TCL_OK) {
          return TCL_ERROR;
      }
      tkwin = Tk_MainWindow(interp);
      block.pixelPtr = NULL;
      dataWidth = 0;
      pixelPtr = NULL;
      for (y = 0; y < dataHeight; ++y) {
          if (Tcl_SplitList(interp, srcArgv[y], &listArgc, &listArgv)
                != TCL_OK) {
            break;
          }
          if (y == 0) {
            dataWidth = listArgc;
            pixelPtr = (unsigned char *) ckalloc((unsigned)
                  dataWidth * dataHeight * 3);
            block.pixelPtr = pixelPtr;
          } else {
            if (listArgc != dataWidth) {
                Tcl_AppendResult(interp, "all elements of color list must",
                       " have the same number of elements",
                      (char *) NULL);
                ckfree((char *) listArgv);
                break;
            }
          }
          for (x = 0; x < dataWidth; ++x) {
            if (!XParseColor(Tk_Display(tkwin), Tk_Colormap(tkwin),
                  listArgv[x], &color)) {
                Tcl_AppendResult(interp, "can't parse color \"",
                      listArgv[x], "\"", (char *) NULL);
                break;
            }
            *pixelPtr++ = color.red >> 8;
            *pixelPtr++ = color.green >> 8;
            *pixelPtr++ = color.blue >> 8;
          }
          ckfree((char *) listArgv);
          if (x < dataWidth)
            break;
      }
      ckfree((char *) srcArgv);
      if (y < dataHeight || dataHeight == 0 || dataWidth == 0) {
          if (block.pixelPtr != NULL) {
            ckfree((char *) block.pixelPtr);
          }
          if (y < dataHeight) {
            return TCL_ERROR;
          }
          return TCL_OK;
      }

      /*
       * Fill in default values for the -to option, then
       * copy the block in using Tk_PhotoPutBlock.
       */

      if (((options.options & OPT_TO) == 0) || (options.toX2 < 0)) {
          options.toX2 = options.toX + dataWidth;
          options.toY2 = options.toY + dataHeight;
      }
      block.width = dataWidth;
      block.height = dataHeight;
      block.pitch = dataWidth * 3;
      block.pixelSize = 3;
      block.offset[0] = 0;
      block.offset[1] = 1;
      block.offset[2] = 2;
      Tk_PhotoPutBlock((ClientData)masterPtr, &block,
            options.toX, options.toY, options.toX2 - options.toX,
            options.toY2 - options.toY);
      ckfree((char *) block.pixelPtr);
    } else if ((c == 'r') && (length >= 3)
             && (strncmp(argv[1], "read", length) == 0)) {
      /*
       * photo read command - first parse the options specified.
       */

      index = 2;
      memset((VOID *) &options, 0, sizeof(options));
      options.name = NULL;
      options.format = NULL;
      if (ParseSubcommandOptions(&options, interp,
            OPT_FORMAT | OPT_FROM | OPT_TO | OPT_SHRINK,
            &index, argc, argv) != TCL_OK) {
          return TCL_ERROR;
      }
      if ((options.name == NULL) || (index < argc)) {
          Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
                " read fileName ?-format format-name?",
                " ?-from x1 y1 x2 y2? ?-to x y? ?-shrink?\"",
                (char *) NULL);
          return TCL_ERROR;
      }

        /*
         * Prevent file system access in safe interpreters.
         */

        if (Tcl_IsSafe(interp)) {
            Tcl_AppendResult(interp, "can't get image from a file in a",
                    " safe interpreter", (char *) NULL);
            return TCL_ERROR;
        }
        
      /*
       * Open the image file and look for a handler for it.
       */

      chan = Tcl_OpenFileChannel(interp, options.name, "r", 0);
      if (chan == NULL) {
          return TCL_ERROR;
      }
        if (Tcl_SetChannelOption(interp, chan, "-translation", "binary")
            != TCL_OK) {
            return TCL_ERROR;
        }
      if (MatchFileFormat(interp, chan, options.name, options.format,
            &imageFormat, &imageWidth, &imageHeight) != TCL_OK) {
          Tcl_Close(NULL, chan);
          return TCL_ERROR;
      }

      /*
       * Check the values given for the -from option.
       */

      if ((options.fromX > imageWidth) || (options.fromY > imageHeight)
            || (options.fromX2 > imageWidth)
            || (options.fromY2 > imageHeight)) {
          Tcl_AppendResult(interp, "coordinates for -from option extend ",
                "outside source image", (char *) NULL);
          Tcl_Close(NULL, chan);
          return TCL_ERROR;
      }
      if (((options.options & OPT_FROM) == 0) || (options.fromX2 < 0)) {
          width = imageWidth - options.fromX;
          height = imageHeight - options.fromY;
      } else {
          width = options.fromX2 - options.fromX;
          height = options.fromY2 - options.fromY;
      }

      /*
       * If the -shrink option was specified, set the size of the image.
       */

      if (options.options & OPT_SHRINK) {
          ImgPhotoSetSize(masterPtr, options.toX + width,
                options.toY + height);
      }

      /*
       * Call the handler's file read procedure to read the data
       * into the image.
       */

      result = (*imageFormat->fileReadProc)(interp, chan, options.name,
            options.format, (Tk_PhotoHandle) masterPtr, options.toX,
            options.toY, width, height, options.fromX, options.fromY);
      if (chan != NULL) {
          Tcl_Close(NULL, chan);
      }
      return result;
    } else if ((c == 'r') && (length >= 3)
             && (strncmp(argv[1], "redither", length) == 0)) {

      if (argc == 2) {
          /*
           * Call Dither if any part of the image is not correctly
           * dithered at present.
           */

          x = masterPtr->ditherX;
          y = masterPtr->ditherY;
          if (masterPtr->ditherX != 0) {
            Dither(masterPtr, x, y, masterPtr->width - x, 1);
          }
          if (masterPtr->ditherY < masterPtr->height) {
            x = 0;
            Dither(masterPtr, 0, masterPtr->ditherY, masterPtr->width,
                  masterPtr->height - masterPtr->ditherY);
          }

          if (y < masterPtr->height) {
            /*
             * Tell the core image code that part of the image has changed.
             */

            Tk_ImageChanged(masterPtr->tkMaster, x, y,
                  (masterPtr->width - x), (masterPtr->height - y),
                  masterPtr->width, masterPtr->height);
          }

      } else {
          Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
                " redither\"", (char *) NULL);
          return TCL_ERROR;
      }
    } else if ((c == 'w') && (strncmp(argv[1], "write", length) == 0)) {

        /*
         * Prevent file system access in safe interpreters.
         */

        if (Tcl_IsSafe(interp)) {
            Tcl_AppendResult(interp, "can't write image to a file in a",
                    " safe interpreter", (char *) NULL);
            return TCL_ERROR;
        }
        
      /*
       * photo write command - first parse and check any options given.
       */

      index = 2;
      memset((VOID *) &options, 0, sizeof(options));
      options.name = NULL;
      options.format = NULL;
      if (ParseSubcommandOptions(&options, interp, OPT_FORMAT | OPT_FROM,
            &index, argc, argv) != TCL_OK) {
          return TCL_ERROR;
      }
      if ((options.name == NULL) || (index < argc)) {
          Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
                " write fileName ?-format format-name?",
                "?-from x1 y1 x2 y2?\"", (char *) NULL);
          return TCL_ERROR;
      }
      if ((options.fromX > masterPtr->width)
            || (options.fromY > masterPtr->height)
            || (options.fromX2 > masterPtr->width)
            || (options.fromY2 > masterPtr->height)) {
          Tcl_AppendResult(interp, "coordinates for -from option extend ",
                "outside image", (char *) NULL);
          return TCL_ERROR;
      }

      /*
       * Fill in default values for unspecified parameters.
       */

      if (((options.options & OPT_FROM) == 0) || (options.fromX2 < 0)) {
          options.fromX2 = masterPtr->width;
          options.fromY2 = masterPtr->height;
      }

      /*
       * Search for an appropriate image file format handler,
       * and give an error if none is found.
       */

      matched = 0;
      for (imageFormat = formatList; imageFormat != NULL;
           imageFormat = imageFormat->nextPtr) {
          if ((options.format == NULL)
                || (strncasecmp(options.format, imageFormat->name,
                strlen(imageFormat->name)) == 0)) {
            matched = 1;
            if (imageFormat->fileWriteProc != NULL) {
                break;
            }
          }
      }
      if (imageFormat == NULL) {
          if (options.format == NULL) {
            Tcl_AppendResult(interp, "no available image file format ",
                  "has file writing capability", (char *) NULL);
          } else if (!matched) {
            Tcl_AppendResult(interp, "image file format \"",
                  options.format, "\" is unknown", (char *) NULL);
          } else {
            Tcl_AppendResult(interp, "image file format \"",
                  options.format, "\" has no file writing capability",
                  (char *) NULL);
          }
          return TCL_ERROR;
      }

      /*
       * Call the handler's file write procedure to write out
       * the image.
       */

      Tk_PhotoGetImage((Tk_PhotoHandle) masterPtr, &block);
      block.pixelPtr += options.fromY * block.pitch + options.fromX * 3;
      block.width = options.fromX2 - options.fromX;
      block.height = options.fromY2 - options.fromY;
      return (*imageFormat->fileWriteProc)(interp, options.name,
            options.format, &block);
    } else {
      Tcl_AppendResult(interp, "bad option \"", argv[1],
            "\": must be blank, cget, configure, copy, get, put,",
            " read, redither, or write", (char *) NULL);
      return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ParseSubcommandOptions --
 *
 *    This procedure is invoked to process one of the options
 *    which may be specified for the photo image subcommands,
 *    namely, -from, -to, -zoom, -subsample, -format, and -shrink.
 *
 * Results:
 *    A standard Tcl result.
 *
 * Side effects:
 *    Fields in *optPtr get filled in.
 *
 *----------------------------------------------------------------------
 */

static int
ParseSubcommandOptions(optPtr, interp, allowedOptions, optIndexPtr, argc, argv)
    struct SubcommandOptions *optPtr;
                        /* Information about the options specified
                         * and the values given is returned here. */
    Tcl_Interp *interp;       /* Interpreter to use for reporting errors. */
    int allowedOptions;       /* Indicates which options are valid for
                         * the current command. */
    int *optIndexPtr;         /* Points to a variable containing the
                         * current index in argv; this variable is
                         * updated by this procedure. */
    int argc;                 /* Number of arguments in argv[]. */
    char **argv;        /* Arguments to be parsed. */
{
    int index, c, bit, currentBit;
    size_t length;
    char *option, **listPtr;
    int values[4];
    int numValues, maxValues, argIndex;

    for (index = *optIndexPtr; index < argc; *optIndexPtr = ++index) {
      /*
       * We can have one value specified without an option;
       * it goes into optPtr->name.
       */

      option = argv[index];
      if (option[0] != '-') {
          if (optPtr->name == NULL) {
            optPtr->name = option;
            continue;
          }
          break;
      }

      /*
       * Work out which option this is.
       */

      length = strlen(option);
      c = option[0];
      bit = 0;
      currentBit = 1;
      for (listPtr = optionNames; *listPtr != NULL; ++listPtr) {
          if ((c == *listPtr[0])
                && (strncmp(option, *listPtr, length) == 0)) {
            if (bit != 0) {
                bit = 0;      /* An ambiguous option. */
                break;
            }
            bit = currentBit;
          }
          currentBit <<= 1;
      }

      /*
       * If this option is not recognized and allowed, put
       * an error message in the interpreter and return.
       */

      if ((allowedOptions & bit) == 0) {
          Tcl_AppendResult(interp, "unrecognized option \"", argv[index],
                "\": must be ", (char *)NULL);
          bit = 1;
          for (listPtr = optionNames; *listPtr != NULL; ++listPtr) {
            if ((allowedOptions & bit) != 0) {
                if ((allowedOptions & (bit - 1)) != 0) {
                  Tcl_AppendResult(interp, ", ", (char *) NULL);
                  if ((allowedOptions & ~((bit << 1) - 1)) == 0) {
                      Tcl_AppendResult(interp, "or ", (char *) NULL);
                  }
                }
                Tcl_AppendResult(interp, *listPtr, (char *) NULL);
            }
            bit <<= 1;
          }
          return TCL_ERROR;
      }

      /*
       * For the -from, -to, -zoom and -subsample options,
       * parse the values given.  Report an error if too few
       * or too many values are given.
       */

      if ((bit != OPT_SHRINK) && (bit != OPT_FORMAT)) {
          maxValues = ((bit == OPT_FROM) || (bit == OPT_TO))? 4: 2;
          argIndex = index + 1;
          for (numValues = 0; numValues < maxValues; ++numValues) {
            if ((argIndex < argc) && (isdigit(UCHAR(argv[argIndex][0]))
                  || ((argv[argIndex][0] == '-')
                  && (isdigit(UCHAR(argv[argIndex][1])))))) {
                if (Tcl_GetInt(interp, argv[argIndex], &values[numValues])
                      != TCL_OK) {
                  return TCL_ERROR;
                }
            } else {
                break;
            }
            ++argIndex;
          }

          if (numValues == 0) {
            Tcl_AppendResult(interp, "the \"", argv[index], "\" option ",
                   "requires one ", maxValues == 2? "or two": "to four",
                   " integer values", (char *) NULL);
            return TCL_ERROR;
          }
          *optIndexPtr = (index += numValues);

          /*
           * Y values default to the corresponding X value if not specified.
           */

          if (numValues == 1) {
            values[1] = values[0];
          }
          if (numValues == 3) {
            values[3] = values[2];
          }

          /*
           * Check the values given and put them in the appropriate
           * field of the SubcommandOptions structure.
           */

          switch (bit) {
            case OPT_FROM:
                if ((values[0] < 0) || (values[1] < 0) || ((numValues > 2)
                      && ((values[2] < 0) || (values[3] < 0)))) {
                  Tcl_AppendResult(interp, "value(s) for the -from",
                        " option must be non-negative", (char *) NULL);
                  return TCL_ERROR;
                }
                if (numValues <= 2) {
                  optPtr->fromX = values[0];
                  optPtr->fromY = values[1];
                  optPtr->fromX2 = -1;
                  optPtr->fromY2 = -1;
                } else {
                  optPtr->fromX = MIN(values[0], values[2]);
                  optPtr->fromY = MIN(values[1], values[3]);
                  optPtr->fromX2 = MAX(values[0], values[2]);
                  optPtr->fromY2 = MAX(values[1], values[3]);
                }
                break;
            case OPT_SUBSAMPLE:
                optPtr->subsampleX = values[0];
                optPtr->subsampleY = values[1];
                break;
            case OPT_TO:
                if ((values[0] < 0) || (values[1] < 0) || ((numValues > 2)
                      && ((values[2] < 0) || (values[3] < 0)))) {
                  Tcl_AppendResult(interp, "value(s) for the -to",
                        " option must be non-negative", (char *) NULL);
                  return TCL_ERROR;
                }
                if (numValues <= 2) {
                  optPtr->toX = values[0];
                  optPtr->toY = values[1];
                  optPtr->toX2 = -1;
                  optPtr->toY2 = -1;
                } else {
                  optPtr->toX = MIN(values[0], values[2]);
                  optPtr->toY = MIN(values[1], values[3]);
                  optPtr->toX2 = MAX(values[0], values[2]);
                  optPtr->toY2 = MAX(values[1], values[3]);
                }
                break;
            case OPT_ZOOM:
                if ((values[0] <= 0) || (values[1] <= 0)) {
                  Tcl_AppendResult(interp, "value(s) for the -zoom",
                        " option must be positive", (char *) NULL);
                  return TCL_ERROR;
                }
                optPtr->zoomX = values[0];
                optPtr->zoomY = values[1];
                break;
          }
      } else if (bit == OPT_FORMAT) {
          /*
           * The -format option takes a single string value.
           */

          if (index + 1 < argc) {
            *optIndexPtr = ++index;
            optPtr->format = argv[index];
          } else {
            Tcl_AppendResult(interp, "the \"-format\" option ",
                  "requires a value", (char *) NULL);
            return TCL_ERROR;
          }
      }

      /*
       * Remember that we saw this option.
       */

      optPtr->options |= bit;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoConfigureMaster --
 *
 *    This procedure is called when a photo image is created or
 *    reconfigured.  It processes configuration options and resets
 *    any instances of the image.
 *
 * Results:
 *    A standard Tcl return value.  If TCL_ERROR is returned then
 *    an error message is left in masterPtr->interp->result.
 *
 * Side effects:
 *    Existing instances of the image will be redisplayed to match
 *    the new configuration options.
 *
 *----------------------------------------------------------------------
 */

static int
ImgPhotoConfigureMaster(interp, masterPtr, argc, argv, flags)
    Tcl_Interp *interp;       /* Interpreter to use for reporting errors. */
    PhotoMaster *masterPtr;   /* Pointer to data structure describing
                         * overall photo image to (re)configure. */
    int argc;                 /* Number of entries in argv. */
    char **argv;        /* Pairs of configuration options for image. */
    int flags;                /* Flags to pass to Tk_ConfigureWidget,
                         * such as TK_CONFIG_ARGV_ONLY. */
{
    PhotoInstance *instancePtr;
    char *oldFileString, *oldDataString, *oldPaletteString;
    double oldGamma;
    int result;
    Tcl_Channel chan;
    Tk_PhotoImageFormat *imageFormat;
    int imageWidth, imageHeight;

    /*
     * Save the current values for fileString and dataString, so we
     * can tell if the user specifies them anew.
     */

    oldFileString = masterPtr->fileString;
    oldDataString = (oldFileString == NULL)? masterPtr->dataString: NULL;
    oldPaletteString = masterPtr->palette;
    oldGamma = masterPtr->gamma;

    /*
     * Process the configuration options specified.
     */

    if (Tk_ConfigureWidget(interp, Tk_MainWindow(interp), configSpecs,
          argc, argv, (char *) masterPtr, flags) != TCL_OK) {
      return TCL_ERROR;
    }

    /*
     * Regard the empty string for -file, -data or -format as the null
     * value.
     */

    if ((masterPtr->fileString != NULL) && (masterPtr->fileString[0] == 0)) {
      ckfree(masterPtr->fileString);
      masterPtr->fileString = NULL;
    }
    if ((masterPtr->dataString != NULL) && (masterPtr->dataString[0] == 0)) {
      ckfree(masterPtr->dataString);
      masterPtr->dataString = NULL;
    }
    if ((masterPtr->format != NULL) && (masterPtr->format[0] == 0)) {
      ckfree(masterPtr->format);
      masterPtr->format = NULL;
    }

    /*
     * Set the image to the user-requested size, if any,
     * and make sure storage is correctly allocated for this image.
     */

    ImgPhotoSetSize(masterPtr, masterPtr->width, masterPtr->height);

    /*
     * Read in the image from the file or string if the user has
     * specified the -file or -data option.
     */

    if ((masterPtr->fileString != NULL)
          && (masterPtr->fileString != oldFileString)) {

        /*
         * Prevent file system access in a safe interpreter.
         */

        if (Tcl_IsSafe(interp)) {
            Tcl_AppendResult(interp, "can't get image from a file in a",
                    " safe interpreter", (char *) NULL);
            return TCL_ERROR;
        }
        
      chan = Tcl_OpenFileChannel(interp, masterPtr->fileString, "r", 0);
      if (chan == NULL) {
          return TCL_ERROR;
      }
        if (Tcl_SetChannelOption(interp, chan, "-translation", "binary")
            != TCL_OK) {
            return TCL_ERROR;
        }
      if (MatchFileFormat(interp, chan, masterPtr->fileString,
            masterPtr->format, &imageFormat, &imageWidth,
            &imageHeight) != TCL_OK) {
          Tcl_Close(NULL, chan);
          return TCL_ERROR;
      }
      ImgPhotoSetSize(masterPtr, imageWidth, imageHeight);
      result = (*imageFormat->fileReadProc)(interp, chan,
            masterPtr->fileString, masterPtr->format,
            (Tk_PhotoHandle) masterPtr, 0, 0,
            imageWidth, imageHeight, 0, 0);
      Tcl_Close(NULL, chan);
      if (result != TCL_OK) {
          return TCL_ERROR;
      }

      masterPtr->flags |= IMAGE_CHANGED;
    }

    if ((masterPtr->fileString == NULL) && (masterPtr->dataString != NULL)
          && (masterPtr->dataString != oldDataString)) {

      if (MatchStringFormat(interp, masterPtr->dataString, 
            masterPtr->format, &imageFormat, &imageWidth,
            &imageHeight) != TCL_OK) {
          return TCL_ERROR;
      }
      ImgPhotoSetSize(masterPtr, imageWidth, imageHeight);
      if ((*imageFormat->stringReadProc)(interp, masterPtr->dataString,
            masterPtr->format, (Tk_PhotoHandle) masterPtr,
            0, 0, imageWidth, imageHeight, 0, 0) != TCL_OK) {
          return TCL_ERROR;
      }

      masterPtr->flags |= IMAGE_CHANGED;
    }

    /*
     * Enforce a reasonable value for gamma.
     */

    if (masterPtr->gamma <= 0) {
      masterPtr->gamma = 1.0;
    }

    if ((masterPtr->gamma != oldGamma)
          || (masterPtr->palette != oldPaletteString)) {
      masterPtr->flags |= IMAGE_CHANGED;
    }

    /*
     * Cycle through all of the instances of this image, regenerating
     * the information for each instance.  Then force the image to be
     * redisplayed everywhere that it is used.
     */

    for (instancePtr = masterPtr->instancePtr; instancePtr != NULL;
          instancePtr = instancePtr->nextPtr) {
      ImgPhotoConfigureInstance(instancePtr);
    }

    /*
     * Inform the generic image code that the image
     * has (potentially) changed.
     */

    Tk_ImageChanged(masterPtr->tkMaster, 0, 0, masterPtr->width,
          masterPtr->height, masterPtr->width, masterPtr->height);
    masterPtr->flags &= ~IMAGE_CHANGED;

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoConfigureInstance --
 *
 *    This procedure is called to create displaying information for
 *    a photo image instance based on the configuration information
 *    in the master.  It is invoked both when new instances are
 *    created and when the master is reconfigured.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Generates errors via Tcl_BackgroundError if there are problems
 *    in setting up the instance.
 *
 *----------------------------------------------------------------------
 */

static void
ImgPhotoConfigureInstance(instancePtr)
    PhotoInstance *instancePtr;     /* Instance to reconfigure. */
{
    PhotoMaster *masterPtr = instancePtr->masterPtr;
    XImage *imagePtr;
    int bitsPerPixel;
    ColorTable *colorTablePtr;
    XRectangle validBox;

    /*
     * If the -palette configuration option has been set for the master,
     * use the value specified for our palette, but only if it is
     * a valid palette for our windows.  Use the gamma value specified
     * the master.
     */

    if ((masterPtr->palette && masterPtr->palette[0])
          && IsValidPalette(instancePtr, masterPtr->palette)) {
      instancePtr->palette = masterPtr->palette;
    } else {
      instancePtr->palette = instancePtr->defaultPalette;
    }
    instancePtr->gamma = masterPtr->gamma;

    /*
     * If we don't currently have a color table, or if the one we
     * have no longer applies (e.g. because our palette or gamma
     * has changed), get a new one.
     */

    colorTablePtr = instancePtr->colorTablePtr;
    if ((colorTablePtr == NULL)
          || (instancePtr->colormap != colorTablePtr->id.colormap)
          || (instancePtr->palette != colorTablePtr->id.palette)
          || (instancePtr->gamma != colorTablePtr->id.gamma)) {
      /*
       * Free up our old color table, and get a new one.
       */

      if (colorTablePtr != NULL) {
          colorTablePtr->liveRefCount -= 1;
          FreeColorTable(colorTablePtr);
      }
      GetColorTable(instancePtr);

      /*
       * Create a new XImage structure for sending data to
       * the X server, if necessary.
       */

      if (instancePtr->colorTablePtr->flags & BLACK_AND_WHITE) {
          bitsPerPixel = 1;
      } else {
          bitsPerPixel = instancePtr->visualInfo.depth;
      }

      if ((instancePtr->imagePtr == NULL)
            || (instancePtr->imagePtr->bits_per_pixel != bitsPerPixel)) {
          if (instancePtr->imagePtr != NULL) {
            XFree((char *) instancePtr->imagePtr);
          }
          imagePtr = XCreateImage(instancePtr->display,
                instancePtr->visualInfo.visual, (unsigned) bitsPerPixel,
                (bitsPerPixel > 1? ZPixmap: XYBitmap), 0, (char *) NULL,
                1, 1, 32, 0);
          instancePtr->imagePtr = imagePtr;

          /*
           * Determine the endianness of this machine.
           * We create images using the local host's endianness, rather
           * than the endianness of the server; otherwise we would have
           * to byte-swap any 16 or 32 bit values that we store in the
           * image in those situations where the server's endianness
           * is different from ours.
           */

          if (imagePtr != NULL) {
            union {
                int i;
                char c[sizeof(int)];
            } kludge;

            imagePtr->bitmap_unit = sizeof(pixel) * NBBY;
            kludge.i = 0;
            kludge.c[0] = 1;
            imagePtr->byte_order = (kludge.i == 1) ? LSBFirst : MSBFirst;
            _XInitImageFuncPtrs(imagePtr);
          }
      }
    }

    /*
     * If the user has specified a width and/or height for the master
     * which is different from our current width/height, set the size
     * to the values specified by the user.  If we have no pixmap, we
     * do this also, since it has the side effect of allocating a
     * pixmap for us.
     */

    if ((instancePtr->pixels == None) || (instancePtr->error == NULL)
          || (instancePtr->width != masterPtr->width)
          || (instancePtr->height != masterPtr->height)) {
      ImgPhotoInstanceSetSize(instancePtr);
    }

    /*
     * Redither this instance if necessary.
     */

    if ((masterPtr->flags & IMAGE_CHANGED)
          || (instancePtr->colorTablePtr != colorTablePtr)) {
      TkClipBox(masterPtr->validRegion, &validBox);
      if ((validBox.width > 0) && (validBox.height > 0)) {
          DitherInstance(instancePtr, validBox.x, validBox.y,
                validBox.width, validBox.height);
      }
    }

}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoGet --
 *
 *    This procedure is called for each use of a photo image in a
 *    widget.
 *
 * Results:
 *    The return value is a token for the instance, which is passed
 *    back to us in calls to ImgPhotoDisplay and ImgPhotoFree.
 *
 * Side effects:
 *    A data structure is set up for the instance (or, an existing
 *    instance is re-used for the new one).
 *
 *----------------------------------------------------------------------
 */

static ClientData
ImgPhotoGet(tkwin, masterData)
    Tk_Window tkwin;          /* Window in which the instance will be
                         * used. */
    ClientData masterData;    /* Pointer to our master structure for the
                         * image. */
{
    PhotoMaster *masterPtr = (PhotoMaster *) masterData;
    PhotoInstance *instancePtr;
    Colormap colormap;
    int mono, nRed, nGreen, nBlue;
    XVisualInfo visualInfo, *visInfoPtr;
    XRectangle validBox;
    char buf[16];
    int numVisuals;
    XColor *white, *black;
    XGCValues gcValues;

    /*
     * Table of "best" choices for palette for PseudoColor displays
     * with between 3 and 15 bits/pixel.
     */

    static int paletteChoice[13][3] = {
      /*  #red, #green, #blue */
       {2,  2,  2,                  /* 3 bits, 8 colors */},
       {2,  3,  2,                  /* 4 bits, 12 colors */},
       {3,  4,  2,                  /* 5 bits, 24 colors */},
       {4,  5,  3,                  /* 6 bits, 60 colors */},
       {5,  6,  4,                  /* 7 bits, 120 colors */},
       {7,  7,  4,                  /* 8 bits, 198 colors */},
       {8, 10,  6,                  /* 9 bits, 480 colors */},
      {10, 12,  8,                  /* 10 bits, 960 colors */},
      {14, 15,  9,                  /* 11 bits, 1890 colors */},
      {16, 20, 12,                  /* 12 bits, 3840 colors */},
      {20, 24, 16,                  /* 13 bits, 7680 colors */},
      {26, 30, 20,                  /* 14 bits, 15600 colors */},
      {32, 32, 30,                  /* 15 bits, 30720 colors */}
    };

    /*
     * See if there is already an instance for windows using
     * the same colormap.  If so then just re-use it.
     */

    colormap = Tk_Colormap(tkwin);
    for (instancePtr = masterPtr->instancePtr; instancePtr != NULL;
          instancePtr = instancePtr->nextPtr) {
      if ((colormap == instancePtr->colormap)
            && (Tk_Display(tkwin) == instancePtr->display)) {

          /*
           * Re-use this instance.
           */

          if (instancePtr->refCount == 0) {
            /*
             * We are resurrecting this instance.
             */

            Tcl_CancelIdleCall(DisposeInstance, (ClientData) instancePtr);
            if (instancePtr->colorTablePtr != NULL) {
                FreeColorTable(instancePtr->colorTablePtr);
            }
            GetColorTable(instancePtr);
          }
          instancePtr->refCount++;
          return (ClientData) instancePtr;
      }
    }

    /*
     * The image isn't already in use in a window with the same colormap.
     * Make a new instance of the image.
     */

    instancePtr = (PhotoInstance *) ckalloc(sizeof(PhotoInstance));
    instancePtr->masterPtr = masterPtr;
    instancePtr->display = Tk_Display(tkwin);
    instancePtr->colormap = Tk_Colormap(tkwin);
    Tk_PreserveColormap(instancePtr->display, instancePtr->colormap);
    instancePtr->refCount = 1;
    instancePtr->colorTablePtr = NULL;
    instancePtr->pixels = None;
    instancePtr->error = NULL;
    instancePtr->width = 0;
    instancePtr->height = 0;
    instancePtr->imagePtr = 0;
    instancePtr->nextPtr = masterPtr->instancePtr;
    masterPtr->instancePtr = instancePtr;

    /*
     * Obtain information about the visual and decide on the
     * default palette.
     */

    visualInfo.screen = Tk_ScreenNumber(tkwin);
    visualInfo.visualid = XVisualIDFromVisual(Tk_Visual(tkwin));
    visInfoPtr = XGetVisualInfo(Tk_Display(tkwin),
          VisualScreenMask | VisualIDMask, &visualInfo, &numVisuals);
    nRed = 2;
    nGreen = nBlue = 0;
    mono = 1;
    if (visInfoPtr != NULL) {
      instancePtr->visualInfo = *visInfoPtr;
      switch (visInfoPtr->class) {
          case DirectColor:
          case TrueColor:
            nRed = 1 << CountBits(visInfoPtr->red_mask);
            nGreen = 1 << CountBits(visInfoPtr->green_mask);
            nBlue = 1 << CountBits(visInfoPtr->blue_mask);
            mono = 0;
            break;
          case PseudoColor:
          case StaticColor:
            if (visInfoPtr->depth > 15) {
                nRed = 32;
                nGreen = 32;
                nBlue = 32;
                mono = 0;
            } else if (visInfoPtr->depth >= 3) {
                int *ip = paletteChoice[visInfoPtr->depth - 3];
    
                nRed = ip[0];
                nGreen = ip[1];
                nBlue = ip[2];
                mono = 0;
            }
            break;
          case GrayScale:
          case StaticGray:
            nRed = 1 << visInfoPtr->depth;
            break;
      }
      XFree((char *) visInfoPtr);

    } else {
      panic("ImgPhotoGet couldn't find visual for window");
    }

    sprintf(buf, ((mono) ? "%d": "%d/%d/%d"), nRed, nGreen, nBlue);
    instancePtr->defaultPalette = Tk_GetUid(buf);

    /*
     * Make a GC with background = black and foreground = white.
     */

    white = Tk_GetColor(masterPtr->interp, tkwin, "white");
    black = Tk_GetColor(masterPtr->interp, tkwin, "black");
    gcValues.foreground = (white != NULL)? white->pixel:
          WhitePixelOfScreen(Tk_Screen(tkwin));
    gcValues.background = (black != NULL)? black->pixel:
          BlackPixelOfScreen(Tk_Screen(tkwin));
    gcValues.graphics_exposures = False;
    instancePtr->gc = Tk_GetGC(tkwin,
          GCForeground|GCBackground|GCGraphicsExposures, &gcValues);

    /*
     * Set configuration options and finish the initialization of the instance.
     */

    ImgPhotoConfigureInstance(instancePtr);

    /*
     * If this is the first instance, must set the size of the image.
     */

    if (instancePtr->nextPtr == NULL) {
      Tk_ImageChanged(masterPtr->tkMaster, 0, 0, 0, 0,
            masterPtr->width, masterPtr->height);
    }

    /*
     * Dither the image to fill in this instance's pixmap.
     */

    TkClipBox(masterPtr->validRegion, &validBox);
    if ((validBox.width > 0) && (validBox.height > 0)) {
      DitherInstance(instancePtr, validBox.x, validBox.y, validBox.width,
            validBox.height);
    }

    return (ClientData) instancePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoDisplay --
 *
 *    This procedure is invoked to draw a photo image.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    A portion of the image gets rendered in a pixmap or window.
 *
 *----------------------------------------------------------------------
 */

static void
ImgPhotoDisplay(clientData, display, drawable, imageX, imageY, width,
      height, drawableX, drawableY)
    ClientData clientData;    /* Pointer to PhotoInstance structure for
                         * for instance to be displayed. */
    Display *display;         /* Display on which to draw image. */
    Drawable drawable;        /* Pixmap or window in which to draw image. */
    int imageX, imageY;       /* Upper-left corner of region within image
                         * to draw. */
    int width, height;        /* Dimensions of region within image to draw. */
    int drawableX, drawableY; /* Coordinates within drawable that
                         * correspond to imageX and imageY. */
{
    PhotoInstance *instancePtr = (PhotoInstance *) clientData;

    /*
     * If there's no pixmap, it means that an error occurred
     * while creating the image instance so it can't be displayed.
     */

    if (instancePtr->pixels == None) {
      return;
    }

    /*
     * masterPtr->region describes which parts of the image contain
     * valid data.  We set this region as the clip mask for the gc,
     * setting its origin appropriately, and use it when drawing the
     * image.
     */

    TkSetRegion(display, instancePtr->gc, instancePtr->masterPtr->validRegion);
    XSetClipOrigin(display, instancePtr->gc, drawableX - imageX,
          drawableY - imageY);
    XCopyArea(display, instancePtr->pixels, drawable, instancePtr->gc,
          imageX, imageY, (unsigned) width, (unsigned) height,
          drawableX, drawableY);
    XSetClipMask(display, instancePtr->gc, None);
    XSetClipOrigin(display, instancePtr->gc, 0, 0);
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoFree --
 *
 *    This procedure is called when a widget ceases to use a
 *    particular instance of an image.  We don't actually get
 *    rid of the instance until later because we may be about
 *    to get this instance again.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Internal data structures get cleaned up, later.
 *
 *----------------------------------------------------------------------
 */

static void
ImgPhotoFree(clientData, display)
    ClientData clientData;    /* Pointer to PhotoInstance structure for
                         * for instance to be displayed. */
    Display *display;         /* Display containing window that used image. */
{
    PhotoInstance *instancePtr = (PhotoInstance *) clientData;
    ColorTable *colorPtr;

    instancePtr->refCount -= 1;
    if (instancePtr->refCount > 0) {
      return;
    }

    /*
     * There are no more uses of the image within this widget.
     * Decrement the count of live uses of its color table, so
     * that its colors can be reclaimed if necessary, and
     * set up an idle call to free the instance structure.
     */

    colorPtr = instancePtr->colorTablePtr;
    if (colorPtr != NULL) {
      colorPtr->liveRefCount -= 1;
    }
    
    Tcl_DoWhenIdle(DisposeInstance, (ClientData) instancePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoDelete --
 *
 *    This procedure is called by the image code to delete the
 *    master structure for an image.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Resources associated with the image get freed.
 *
 *----------------------------------------------------------------------
 */

static void
ImgPhotoDelete(masterData)
    ClientData masterData;    /* Pointer to PhotoMaster structure for
                         * image.  Must not have any more instances. */
{
    PhotoMaster *masterPtr = (PhotoMaster *) masterData;
    PhotoInstance *instancePtr;

    while ((instancePtr = masterPtr->instancePtr) != NULL) {
      if (instancePtr->refCount > 0) {
          panic("tried to delete photo image when instances still exist");
      }
      Tcl_CancelIdleCall(DisposeInstance, (ClientData) instancePtr);
      DisposeInstance((ClientData) instancePtr);
    }
    masterPtr->tkMaster = NULL;
    if (masterPtr->imageCmd != NULL) {
      Tcl_DeleteCommandFromToken(masterPtr->interp, masterPtr->imageCmd);
    }
    if (masterPtr->pix24 != NULL) {
      ckfree((char *) masterPtr->pix24);
    }
    if (masterPtr->validRegion != NULL) {
      TkDestroyRegion(masterPtr->validRegion);
    }
    Tk_FreeOptions(configSpecs, (char *) masterPtr, (Display *) NULL, 0);
    ckfree((char *) masterPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoCmdDeletedProc --
 *
 *    This procedure is invoked when the image command for an image
 *    is deleted.  It deletes the image.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The image is deleted.
 *
 *----------------------------------------------------------------------
 */

static void
ImgPhotoCmdDeletedProc(clientData)
    ClientData clientData;    /* Pointer to PhotoMaster structure for
                         * image. */
{
    PhotoMaster *masterPtr = (PhotoMaster *) clientData;

    masterPtr->imageCmd = NULL;
    if (masterPtr->tkMaster != NULL) {
      Tk_DeleteImage(masterPtr->interp, Tk_NameOfImage(masterPtr->tkMaster));
    }
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoSetSize --
 *
 *    This procedure reallocates the image storage and instance
 *    pixmaps for a photo image, as necessary, to change the
 *    image's size to `width' x `height' pixels.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Storage gets reallocated, for the master and all its instances.
 *
 *----------------------------------------------------------------------
 */

static void
ImgPhotoSetSize(masterPtr, width, height)
    PhotoMaster *masterPtr;
    int width, height;
{
    unsigned char *newPix24;
    int h, offset, pitch;
    unsigned char *srcPtr, *destPtr;
    XRectangle validBox, clipBox;
    TkRegion clipRegion;
    PhotoInstance *instancePtr;

    if (masterPtr->userWidth > 0) {
      width = masterPtr->userWidth;
    }
    if (masterPtr->userHeight > 0) {
      height = masterPtr->userHeight;
    }

    /*
     * We have to trim the valid region if it is currently
     * larger than the new image size.
     */

    TkClipBox(masterPtr->validRegion, &validBox);
    if ((validBox.x + validBox.width > width)
          || (validBox.y + validBox.height > height)) {
      clipBox.x = 0;
      clipBox.y = 0;
      clipBox.width = width;
      clipBox.height = height;
      clipRegion = TkCreateRegion();
      TkUnionRectWithRegion(&clipBox, clipRegion, clipRegion);
      TkIntersectRegion(masterPtr->validRegion, clipRegion,
            masterPtr->validRegion);
      TkDestroyRegion(clipRegion);
      TkClipBox(masterPtr->validRegion, &validBox);
    }

    if ((width != masterPtr->width) || (height != masterPtr->height)
          || (masterPtr->pix24 == NULL)) {

      /*
       * Reallocate storage for the 24-bit image and copy
       * over valid regions.
       */

      pitch = width * 3;
      newPix24 = (unsigned char *) ckalloc((unsigned) (height * pitch));

      /*
       * Zero the new array.  The dithering code shouldn't read the
       * areas outside validBox, but they might be copied to another
       * photo image or written to a file.
       */

      if ((masterPtr->pix24 != NULL)
          && ((width == masterPtr->width) || (width == validBox.width))) {
          if (validBox.y > 0) {
            memset((VOID *) newPix24, 0, (size_t) (validBox.y * pitch));
          }
          h = validBox.y + validBox.height;
          if (h < height) {
            memset((VOID *) (newPix24 + h * pitch), 0,
                  (size_t) ((height - h) * pitch));
          }
      } else {
          memset((VOID *) newPix24, 0, (size_t) (height * pitch));
      }

      if (masterPtr->pix24 != NULL) {

          /*
           * Copy the common area over to the new array array and
           * free the old array.
           */

          if (width == masterPtr->width) {

            /*
             * The region to be copied is contiguous.
             */

            offset = validBox.y * pitch;
            memcpy((VOID *) (newPix24 + offset),
                  (VOID *) (masterPtr->pix24 + offset),
                  (size_t) (validBox.height * pitch));

          } else if ((validBox.width > 0) && (validBox.height > 0)) {

            /*
             * Area to be copied is not contiguous - copy line by line.
             */

            destPtr = newPix24 + (validBox.y * width + validBox.x) * 3;
            srcPtr = masterPtr->pix24 + (validBox.y * masterPtr->width
                  + validBox.x) * 3;
            for (h = validBox.height; h > 0; h--) {
                memcpy((VOID *) destPtr, (VOID *) srcPtr,
                      (size_t) (validBox.width * 3));
                destPtr += width * 3;
                srcPtr += masterPtr->width * 3;
            }
          }

          ckfree((char *) masterPtr->pix24);
      }

      masterPtr->pix24 = newPix24;
      masterPtr->width = width;
      masterPtr->height = height;

      /*
       * Dithering will be correct up to the end of the last
       * pre-existing complete scanline.
       */

      if ((validBox.x > 0) || (validBox.y > 0)) {
          masterPtr->ditherX = 0;
          masterPtr->ditherY = 0;
      } else if (validBox.width == width) {
          if ((int) validBox.height < masterPtr->ditherY) {
            masterPtr->ditherX = 0;
            masterPtr->ditherY = validBox.height;
          }
      } else {
          if ((masterPtr->ditherY > 0)
                || ((int) validBox.width < masterPtr->ditherX)) {
            masterPtr->ditherX = validBox.width;
            masterPtr->ditherY = 0;
          }
      }
    }

    /*
     * Now adjust the sizes of the pixmaps for all of the instances.
     */

    for (instancePtr = masterPtr->instancePtr; instancePtr != NULL;
          instancePtr = instancePtr->nextPtr) {
      ImgPhotoInstanceSetSize(instancePtr);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * ImgPhotoInstanceSetSize --
 *
 *    This procedure reallocates the instance pixmap and dithering
 *    error array for a photo instance, as necessary, to change the
 *    image's size to `width' x `height' pixels.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Storage gets reallocated, here and in the X server.
 *
 *----------------------------------------------------------------------
 */

static void
ImgPhotoInstanceSetSize(instancePtr)
    PhotoInstance *instancePtr;           /* Instance whose size is to be
                               * changed. */
{
    PhotoMaster *masterPtr;
    schar *newError;
    schar *errSrcPtr, *errDestPtr;
    int h, offset;
    XRectangle validBox;
    Pixmap newPixmap;

    masterPtr = instancePtr->masterPtr;
    TkClipBox(masterPtr->validRegion, &validBox);

    if ((instancePtr->width != masterPtr->width)
          || (instancePtr->height != masterPtr->height)
          || (instancePtr->pixels == None)) {
      newPixmap = Tk_GetPixmap(instancePtr->display,
            RootWindow(instancePtr->display,
                instancePtr->visualInfo.screen),
            (masterPtr->width > 0) ? masterPtr->width: 1,
            (masterPtr->height > 0) ? masterPtr->height: 1,
            instancePtr->visualInfo.depth);

      /*
       * The following is a gross hack needed to properly support colormaps
       * under Windows.  Before the pixels can be copied to the pixmap,
       * the relevent colormap must be associated with the drawable.
       * Normally we can infer this association from the window that
       * was used to create the pixmap.  However, in this case we're
       * using the root window, so we have to be more explicit.
       */

      TkSetPixmapColormap(newPixmap, instancePtr->colormap);

      if (instancePtr->pixels != None) {
          /*
           * Copy any common pixels from the old pixmap and free it.
           */
          XCopyArea(instancePtr->display, instancePtr->pixels, newPixmap,
                instancePtr->gc, validBox.x, validBox.y,
                validBox.width, validBox.height, validBox.x, validBox.y);
          Tk_FreePixmap(instancePtr->display, instancePtr->pixels);
      }
      instancePtr->pixels = newPixmap;
    }

    if ((instancePtr->width != masterPtr->width)
          || (instancePtr->height != masterPtr->height)
          || (instancePtr->error == NULL)) {

      newError = (schar *) ckalloc((unsigned)
            (masterPtr->height * masterPtr->width * 3 * sizeof(schar)));

      /*
       * Zero the new array so that we don't get bogus error values
       * propagating into areas we dither later.
       */

      if ((instancePtr->error != NULL)
          && ((instancePtr->width == masterPtr->width)
            || (validBox.width == masterPtr->width))) {
          if (validBox.y > 0) {
            memset((VOID *) newError, 0, (size_t)
                  (validBox.y * masterPtr->width * 3 * sizeof(schar)));
          }
          h = validBox.y + validBox.height;
          if (h < masterPtr->height) {
            memset((VOID *) (newError + h * masterPtr->width * 3), 0,
                  (size_t) ((masterPtr->height - h)
                      * masterPtr->width * 3 * sizeof(schar)));
          }
      } else {
          memset((VOID *) newError, 0, (size_t)
                (masterPtr->height * masterPtr->width * 3 * sizeof(schar)));
      }

      if (instancePtr->error != NULL) {

          /*
           * Copy the common area over to the new array
           * and free the old array.
           */

          if (masterPtr->width == instancePtr->width) {

            offset = validBox.y * masterPtr->width * 3;
            memcpy((VOID *) (newError + offset),
                  (VOID *) (instancePtr->error + offset),
                  (size_t) (validBox.height
                  * masterPtr->width * 3 * sizeof(schar)));

          } else if (validBox.width > 0 && validBox.height > 0) {

            errDestPtr = newError
                  + (validBox.y * masterPtr->width + validBox.x) * 3;
            errSrcPtr = instancePtr->error
                  + (validBox.y * instancePtr->width + validBox.x) * 3;
            for (h = validBox.height; h > 0; --h) {
                memcpy((VOID *) errDestPtr, (VOID *) errSrcPtr,
                      validBox.width * 3 * sizeof(schar));
                errDestPtr += masterPtr->width * 3;
                errSrcPtr += instancePtr->width * 3;
            }
          }
          ckfree((char *) instancePtr->error);
      }

      instancePtr->error = newError;
    }

    instancePtr->width = masterPtr->width;
    instancePtr->height = masterPtr->height;
}

/*
 *----------------------------------------------------------------------
 *
 * IsValidPalette --
 *
 *    This procedure is called to check whether a value given for
 *    the -palette option is valid for a particular instance
 *    of a photo image.
 *
 * Results:
 *    A boolean value: 1 if the palette is acceptable, 0 otherwise.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
IsValidPalette(instancePtr, palette)
    PhotoInstance *instancePtr;           /* Instance to which the palette
                               * specification is to be applied. */
    char *palette;                  /* Palette specification string. */
{
    int nRed, nGreen, nBlue, mono, numColors;
    char *endp;

    /*
     * First parse the specification: it must be of the form
     * %d or %d/%d/%d.
     */

    nRed = strtol(palette, &endp, 10);
    if ((endp == palette) || ((*endp != 0) && (*endp != '/'))
          || (nRed < 2) || (nRed > 256)) {
      return 0;
    }

    if (*endp == 0) {
      mono = 1;
      nGreen = nBlue = nRed;
    } else {
      palette = endp + 1;
      nGreen = strtol(palette, &endp, 10);
      if ((endp == palette) || (*endp != '/') || (nGreen < 2)
            || (nGreen > 256)) {
          return 0;
      }
      palette = endp + 1;
      nBlue = strtol(palette, &endp, 10);
      if ((endp == palette) || (*endp != 0) || (nBlue < 2)
            || (nBlue > 256)) {
          return 0;
      }
      mono = 0;
    }

    switch (instancePtr->visualInfo.class) {
      case DirectColor:
      case TrueColor:
          if ((nRed > (1 << CountBits(instancePtr->visualInfo.red_mask)))
                || (nGreen > (1
                  << CountBits(instancePtr->visualInfo.green_mask)))
                || (nBlue > (1
                  << CountBits(instancePtr->visualInfo.blue_mask)))) {
            return 0;
          }
          break;
      case PseudoColor:
      case StaticColor:
          numColors = nRed;
          if (!mono) {
            numColors *= nGreen*nBlue;
          }
          if (numColors > (1 << instancePtr->visualInfo.depth)) {
            return 0;
          }
          break;
      case GrayScale:
      case StaticGray:
          if (!mono || (nRed > (1 << instancePtr->visualInfo.depth))) {
            return 0;
          }
          break;
    }

    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * CountBits --
 *
 *    This procedure counts how many bits are set to 1 in `mask'.
 *
 * Results:
 *    The integer number of bits.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
CountBits(mask)
    pixel mask;               /* Value to count the 1 bits in. */
{
    int n;

    for( n = 0; mask != 0; mask &= mask - 1 )
      n++;
    return n;
}

/*
 *----------------------------------------------------------------------
 *
 * GetColorTable --
 *
 *    This procedure is called to allocate a table of colormap
 *    information for an instance of a photo image.  Only one such
 *    table is allocated for all photo instances using the same
 *    display, colormap, palette and gamma values, so that the
 *    application need only request a set of colors from the X
 *    server once for all such photo widgets.  This procedure
 *    maintains a hash table to find previously-allocated
 *    ColorTables.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    A new ColorTable may be allocated and placed in the hash
 *    table, and have colors allocated for it.
 *
 *----------------------------------------------------------------------
 */

static void
GetColorTable(instancePtr)
    PhotoInstance *instancePtr;           /* Instance needing a color table. */
{
    ColorTable *colorPtr;
    Tcl_HashEntry *entry;
    ColorTableId id;
    int isNew;

    /*
     * Look for an existing ColorTable in the hash table.
     */

    memset((VOID *) &id, 0, sizeof(id));
    id.display = instancePtr->display;
    id.colormap = instancePtr->colormap;
    id.palette = instancePtr->palette;
    id.gamma = instancePtr->gamma;
    if (!imgPhotoColorHashInitialized) {
      Tcl_InitHashTable(&imgPhotoColorHash, N_COLOR_HASH);
      imgPhotoColorHashInitialized = 1;
    }
    entry = Tcl_CreateHashEntry(&imgPhotoColorHash, (char *) &id, &isNew);

    if (!isNew) {
      /*
       * Re-use the existing entry.
       */

      colorPtr = (ColorTable *) Tcl_GetHashValue(entry);

    } else {
      /*
       * No color table currently available; need to make one.
       */

      colorPtr = (ColorTable *) ckalloc(sizeof(ColorTable));

      /*
       * The following line of code should not normally be needed due
       * to the assignment in the following line.  However, it compensates
       * for bugs in some compilers (HP, for example) where
       * sizeof(ColorTable) is 24 but the assignment only copies 20 bytes,
       * leaving 4 bytes uninitialized;  these cause problems when using
       * the id for lookups in imgPhotoColorHash, and can result in
       * core dumps.
       */

      memset((VOID *) &colorPtr->id, 0, sizeof(ColorTableId));
      colorPtr->id = id;
      Tk_PreserveColormap(colorPtr->id.display, colorPtr->id.colormap);
      colorPtr->flags = 0;
      colorPtr->refCount = 0;
      colorPtr->liveRefCount = 0;
      colorPtr->numColors = 0;
      colorPtr->visualInfo = instancePtr->visualInfo;
      colorPtr->pixelMap = NULL;
      Tcl_SetHashValue(entry, colorPtr);
    }

    colorPtr->refCount++;
    colorPtr->liveRefCount++;
    instancePtr->colorTablePtr = colorPtr;
    if (colorPtr->flags & DISPOSE_PENDING) {
      Tcl_CancelIdleCall(DisposeColorTable, (ClientData) colorPtr);
      colorPtr->flags &= ~DISPOSE_PENDING;
    }

    /*
     * Allocate colors for this color table if necessary.
     */

    if ((colorPtr->numColors == 0)
          && ((colorPtr->flags & BLACK_AND_WHITE) == 0)) {
      AllocateColors(colorPtr);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * FreeColorTable --
 *
 *    This procedure is called when an instance ceases using a
 *    color table.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    If no other instances are using this color table, a when-idle
 *    handler is registered to free up the color table and the colors
 *    allocated for it.
 *
 *----------------------------------------------------------------------
 */

static void
FreeColorTable(colorPtr)
    ColorTable *colorPtr;     /* Pointer to the color table which is
                         * no longer required by an instance. */
{
    colorPtr->refCount--;
    if (colorPtr->refCount > 0) {
      return;
    }
    if ((colorPtr->flags & DISPOSE_PENDING) == 0) {
      Tcl_DoWhenIdle(DisposeColorTable, (ClientData) colorPtr);
      colorPtr->flags |= DISPOSE_PENDING;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * AllocateColors --
 *
 *    This procedure allocates the colors required by a color table,
 *    and sets up the fields in the color table data structure which
 *    are used in dithering.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Colors are allocated from the X server.  Fields in the
 *    color table data structure are updated.
 *
 *----------------------------------------------------------------------
 */

static void
AllocateColors(colorPtr)
    ColorTable *colorPtr;     /* Pointer to the color table requiring
                         * colors to be allocated. */
{
    int i, r, g, b, rMult, mono;
    int numColors, nRed, nGreen, nBlue;
    double fr, fg, fb, igam;
    XColor *colors;
    unsigned long *pixels;

    /* 16-bit intensity value for i/n of full intensity. */
#   define CFRAC(i, n)  ((i) * 65535 / (n))

    /* As for CFRAC, but apply exponent of g. */
#   define CGFRAC(i, n, g)    ((int)(65535 * pow((double)(i) / (n), (g))))

    /*
     * First parse the palette specification to get the required number of
     * shades of each primary.
     */

    mono = sscanf(colorPtr->id.palette, "%d/%d/%d", &nRed, &nGreen, &nBlue)
          <= 1;
    igam = 1.0 / colorPtr->id.gamma;

    /*
     * Each time around this loop, we reduce the number of colors we're
     * trying to allocate until we succeed in allocating all of the colors
     * we need.
     */

    for (;;) {
      /*
       * If we are using 1 bit/pixel, we don't need to allocate
       * any colors (we just use the foreground and background
       * colors in the GC).
       */

      if (mono && (nRed <= 2)) {
          colorPtr->flags |= BLACK_AND_WHITE;
          return;
      }

      /*
       * Calculate the RGB coordinates of the colors we want to
       * allocate and store them in *colors.
       */

      if ((colorPtr->visualInfo.class == DirectColor)
          || (colorPtr->visualInfo.class == TrueColor)) {

          /*
           * Direct/True Color: allocate shades of red, green, blue
           * independently.
           */

          if (mono) {
            numColors = nGreen = nBlue = nRed;
          } else {
            numColors = MAX(MAX(nRed, nGreen), nBlue);
          }
          colors = (XColor *) ckalloc(numColors * sizeof(XColor));

          for (i = 0; i < numColors; ++i) {
            if (igam == 1.0) {
                colors[i].red = CFRAC(i, nRed - 1);
                colors[i].green = CFRAC(i, nGreen - 1);
                colors[i].blue = CFRAC(i, nBlue - 1);
            } else {
                colors[i].red = CGFRAC(i, nRed - 1, igam);
                colors[i].green = CGFRAC(i, nGreen - 1, igam);
                colors[i].blue = CGFRAC(i, nBlue - 1, igam);
            }
          }
      } else {
          /*
           * PseudoColor, StaticColor, GrayScale or StaticGray visual:
           * we have to allocate each color in the color cube separately.
           */

          numColors = (mono) ? nRed: (nRed * nGreen * nBlue);
          colors = (XColor *) ckalloc(numColors * sizeof(XColor));

          if (!mono) {
            /*
             * Color display using a PseudoColor or StaticColor visual.
             */

            i = 0;
            for (r = 0; r < nRed; ++r) {
                for (g = 0; g < nGreen; ++g) {
                  for (b = 0; b < nBlue; ++b) {
                      if (igam == 1.0) {
                        colors[i].red = CFRAC(r, nRed - 1);
                        colors[i].green = CFRAC(g, nGreen - 1);
                        colors[i].blue = CFRAC(b, nBlue - 1);
                      } else {
                        colors[i].red = CGFRAC(r, nRed - 1, igam);
                        colors[i].green = CGFRAC(g, nGreen - 1, igam);
                        colors[i].blue = CGFRAC(b, nBlue - 1, igam);
                      }
                      i++;
                  }
                }
            }
          } else {
            /*
             * Monochrome display - allocate the shades of grey we want.
             */

            for (i = 0; i < numColors; ++i) {
                if (igam == 1.0) {
                  r = CFRAC(i, numColors - 1);
                } else {
                  r = CGFRAC(i, numColors - 1, igam);
                }
                colors[i].red = colors[i].green = colors[i].blue = r;
            }
          }
      }

      /*
       * Now try to allocate the colors we've calculated.
       */

      pixels = (unsigned long *) ckalloc(numColors * sizeof(unsigned long));
      for (i = 0; i < numColors; ++i) {
          if (!XAllocColor(colorPtr->id.display, colorPtr->id.colormap,
                &colors[i])) {

            /*
             * Can't get all the colors we want in the default colormap;
             * first try freeing colors from other unused color tables.
             */

            if (!ReclaimColors(&colorPtr->id, numColors - i)
                  || !XAllocColor(colorPtr->id.display,
                  colorPtr->id.colormap, &colors[i])) {
                /*
                 * Still can't allocate the color.
                 */
                break;
            }
          }
          pixels[i] = colors[i].pixel;
      }

      /*
       * If we didn't get all of the colors, reduce the
       * resolution of the color cube, free the ones we got,
       * and try again.
       */

      if (i >= numColors) {
          break;
      }
      XFreeColors(colorPtr->id.display, colorPtr->id.colormap, pixels, i, 0);
      ckfree((char *) colors);
      ckfree((char *) pixels);

      if (!mono) {
          if ((nRed == 2) && (nGreen == 2) && (nBlue == 2)) {
            /*
             * Fall back to 1-bit monochrome display.
             */

            mono = 1;
          } else {
            /*
             * Reduce the number of shades of each primary to about
             * 3/4 of the previous value.  This should reduce the
             * total number of colors required to about half the
             * previous value for PseudoColor displays.
             */

            nRed = (nRed * 3 + 2) / 4;
            nGreen = (nGreen * 3 + 2) / 4;
            nBlue = (nBlue * 3 + 2) / 4;
          }
      } else {
          /*
           * Reduce the number of shades of gray to about 1/2.
           */

          nRed = nRed / 2;
      }
    }
    
    /*
     * We have allocated all of the necessary colors:
     * fill in various fields of the ColorTable record.
     */

    if (!mono) {
      colorPtr->flags |= COLOR_WINDOW;

      /*
       * The following is a hairy hack.  We only want to index into
       * the pixelMap on colormap displays.  However, if the display
       * is on Windows, then we actually want to store the index not
       * the value since we will be passing the color table into the
       * TkPutImage call.
       */
      
#ifndef __WIN32__
      if ((colorPtr->visualInfo.class != DirectColor)
            && (colorPtr->visualInfo.class != TrueColor)) {
          colorPtr->flags |= MAP_COLORS;
      }
#endif /* __WIN32__ */
    }

    colorPtr->numColors = numColors;
    colorPtr->pixelMap = pixels;

    /*
     * Set up quantization tables for dithering.
     */
    rMult = nGreen * nBlue;
    for (i = 0; i < 256; ++i) {
      r = (i * (nRed - 1) + 127) / 255;
      if (mono) {
          fr = (double) colors[r].red / 65535.0;
          if (colorPtr->id.gamma != 1.0 ) {
            fr = pow(fr, colorPtr->id.gamma);
          }
          colorPtr->colorQuant[0][i] = (int)(fr * 255.99);
          colorPtr->redValues[i] = colors[r].pixel;
      } else {
          g = (i * (nGreen - 1) + 127) / 255;
          b = (i * (nBlue - 1) + 127) / 255;
          if ((colorPtr->visualInfo.class == DirectColor)
                || (colorPtr->visualInfo.class == TrueColor)) {
            colorPtr->redValues[i] = colors[r].pixel
                & colorPtr->visualInfo.red_mask;
            colorPtr->greenValues[i] = colors[g].pixel
                & colorPtr->visualInfo.green_mask;
            colorPtr->blueValues[i] = colors[b].pixel
                & colorPtr->visualInfo.blue_mask;
          } else {
            r *= rMult;
            g *= nBlue;
            colorPtr->redValues[i] = r;
            colorPtr->greenValues[i] = g;
            colorPtr->blueValues[i] = b;
          }
          fr = (double) colors[r].red / 65535.0;
          fg = (double) colors[g].green / 65535.0;
          fb = (double) colors[b].blue / 65535.0;
          if (colorPtr->id.gamma != 1.0) {
            fr = pow(fr, colorPtr->id.gamma);
            fg = pow(fg, colorPtr->id.gamma);
            fb = pow(fb, colorPtr->id.gamma);
          }
          colorPtr->colorQuant[0][i] = (int)(fr * 255.99);
          colorPtr->colorQuant[1][i] = (int)(fg * 255.99);
          colorPtr->colorQuant[2][i] = (int)(fb * 255.99);
      }
    }

    ckfree((char *) colors);
}

/*
 *----------------------------------------------------------------------
 *
 * DisposeColorTable --
 *
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The colors in the argument color table are freed, as is the
 *    color table structure itself.  The color table is removed
 *    from the hash table which is used to locate color tables.
 *
 *----------------------------------------------------------------------
 */

static void
DisposeColorTable(clientData)
    ClientData clientData;    /* Pointer to the ColorTable whose
                         * colors are to be released. */
{
    ColorTable *colorPtr;
    Tcl_HashEntry *entry;

    colorPtr = (ColorTable *) clientData;
    if (colorPtr->pixelMap != NULL) {
      if (colorPtr->numColors > 0) {
          XFreeColors(colorPtr->id.display, colorPtr->id.colormap,
                colorPtr->pixelMap, colorPtr->numColors, 0);
          Tk_FreeColormap(colorPtr->id.display, colorPtr->id.colormap);
      }
      ckfree((char *) colorPtr->pixelMap);
    }

    entry = Tcl_FindHashEntry(&imgPhotoColorHash, (char *) &colorPtr->id);
    if (entry == NULL) {
      panic("DisposeColorTable couldn't find hash entry");
    }
    Tcl_DeleteHashEntry(entry);

    ckfree((char *) colorPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * ReclaimColors --
 *
 *    This procedure is called to try to free up colors in the
 *    colormap used by a color table.  It looks for other color
 *    tables with the same colormap and with a zero live reference
 *    count, and frees their colors.  It only does so if there is
 *    the possibility of freeing up at least `numColors' colors.
 *
 * Results:
 *    The return value is TRUE if any colors were freed, FALSE
 *    otherwise.
 *
 * Side effects:
 *    ColorTables which are not currently in use may lose their
 *    color allocations.
 *
 *---------------------------------------------------------------------- */

static int
ReclaimColors(id, numColors)
    ColorTableId *id;         /* Pointer to information identifying
                         * the color table which needs more colors. */
    int numColors;            /* Number of colors required. */
{
    Tcl_HashSearch srch;
    Tcl_HashEntry *entry;
    ColorTable *colorPtr;
    int nAvail;

    /*
     * First scan through the color hash table to get an
     * upper bound on how many colors we might be able to free.
     */

    nAvail = 0;
    entry = Tcl_FirstHashEntry(&imgPhotoColorHash, &srch);
    while (entry != NULL) {
      colorPtr = (ColorTable *) Tcl_GetHashValue(entry);
      if ((colorPtr->id.display == id->display)
          && (colorPtr->id.colormap == id->colormap)
          && (colorPtr->liveRefCount == 0 )&& (colorPtr->numColors != 0)
          && ((colorPtr->id.palette != id->palette)
            || (colorPtr->id.gamma != id->gamma))) {

          /*
           * We could take this guy's colors off him.
           */

          nAvail += colorPtr->numColors;
      }
      entry = Tcl_NextHashEntry(&srch);
    }

    /*
     * nAvail is an (over)estimate of the number of colors we could free.
     */

    if (nAvail < numColors) {
      return 0;
    }

    /*
     * Scan through a second time freeing colors.
     */

    entry = Tcl_FirstHashEntry(&imgPhotoColorHash, &srch);
    while ((entry != NULL) && (numColors > 0)) {
      colorPtr = (ColorTable *) Tcl_GetHashValue(entry);
      if ((colorPtr->id.display == id->display)
            && (colorPtr->id.colormap == id->colormap)
            && (colorPtr->liveRefCount == 0) && (colorPtr->numColors != 0)
            && ((colorPtr->id.palette != id->palette)
                || (colorPtr->id.gamma != id->gamma))) {

          /*
           * Free the colors that this ColorTable has.
           */

          XFreeColors(colorPtr->id.display, colorPtr->id.colormap,
                colorPtr->pixelMap, colorPtr->numColors, 0);
          numColors -= colorPtr->numColors;
          colorPtr->numColors = 0;
          ckfree((char *) colorPtr->pixelMap);
          colorPtr->pixelMap = NULL;
      }

      entry = Tcl_NextHashEntry(&srch);
    }
    return 1;                 /* we freed some colors */
}

/*
 *----------------------------------------------------------------------
 *
 * DisposeInstance --
 *
 *    This procedure is called to finally free up an instance
 *    of a photo image which is no longer required.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The instance data structure and the resources it references
 *    are freed.
 *
 *----------------------------------------------------------------------
 */

static void
DisposeInstance(clientData)
    ClientData clientData;    /* Pointer to the instance whose resources
                         * are to be released. */
{
    PhotoInstance *instancePtr = (PhotoInstance *) clientData;
    PhotoInstance *prevPtr;

    if (instancePtr->pixels != None) {
      Tk_FreePixmap(instancePtr->display, instancePtr->pixels);
    }
    if (instancePtr->gc != None) {
      Tk_FreeGC(instancePtr->display, instancePtr->gc);
    }
    if (instancePtr->imagePtr != NULL) {
      XFree((char *) instancePtr->imagePtr);
    }
    if (instancePtr->error != NULL) {
      ckfree((char *) instancePtr->error);
    }
    if (instancePtr->colorTablePtr != NULL) {
      FreeColorTable(instancePtr->colorTablePtr);
    }

    if (instancePtr->masterPtr->instancePtr == instancePtr) {
      instancePtr->masterPtr->instancePtr = instancePtr->nextPtr;
    } else {
      for (prevPtr = instancePtr->masterPtr->instancePtr;
            prevPtr->nextPtr != instancePtr; prevPtr = prevPtr->nextPtr) {
          /* Empty loop body */
      }
      prevPtr->nextPtr = instancePtr->nextPtr;
    }
    Tk_FreeColormap(instancePtr->display, instancePtr->colormap);
    ckfree((char *) instancePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * MatchFileFormat --
 *
 *    This procedure is called to find a photo image file format
 *    handler which can parse the image data in the given file.
 *    If a user-specified format string is provided, only handlers
 *    whose names match a prefix of the format string are tried.
 *
 * Results:
 *    A standard TCL return value.  If the return value is TCL_OK, a
 *    pointer to the image format record is returned in
 *    *imageFormatPtr, and the width and height of the image are
 *    returned in *widthPtr and *heightPtr.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
MatchFileFormat(interp, chan, fileName, formatString, imageFormatPtr,
      widthPtr, heightPtr)
    Tcl_Interp *interp;       /* Interpreter to use for reporting errors. */
    Tcl_Channel chan;         /* The image file, open for reading. */
    char *fileName;           /* The name of the image file. */
    char *formatString;       /* User-specified format string, or NULL. */
    Tk_PhotoImageFormat **imageFormatPtr;
                        /* A pointer to the photo image format
                         * record is returned here. */
    int *widthPtr, *heightPtr;      /* The dimensions of the image are
                         * returned here. */
{
    int matched;
    Tk_PhotoImageFormat *formatPtr;

    /*
     * Scan through the table of file format handlers to find
     * one which can handle the image.
     */

    matched = 0;
    for (formatPtr = formatList; formatPtr != NULL;
       formatPtr = formatPtr->nextPtr) {
      if (formatString != NULL) {
          if (strncasecmp(formatString, formatPtr->name,
                strlen(formatPtr->name)) != 0) {
            continue;
          }
          matched = 1;
          if (formatPtr->fileMatchProc == NULL) {
            Tcl_AppendResult(interp, "-file option isn't supported for ",
                  formatString, " images", (char *) NULL);
            return TCL_ERROR;
          }
      }
      if (formatPtr->fileMatchProc != NULL) {
          (void) Tcl_Seek(chan, 0L, SEEK_SET);
          
          if ((*formatPtr->fileMatchProc)(chan, fileName, formatString,
                widthPtr, heightPtr)) {
            if (*widthPtr < 1) {
                *widthPtr = 1;
            }
            if (*heightPtr < 1) {
                *heightPtr = 1;
            }
            break;
          }
      }
    }

    if (formatPtr == NULL) {
      if ((formatString != NULL) && !matched) {
          Tcl_AppendResult(interp, "image file format \"", formatString,
                "\" is not supported", (char *) NULL);
      } else {
          Tcl_AppendResult(interp,
                "couldn't recognize data in image file \"",
                fileName, "\"", (char *) NULL);
      }
      return TCL_ERROR;
    }

    *imageFormatPtr = formatPtr;
    (void) Tcl_Seek(chan, 0L, SEEK_SET);
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * MatchStringFormat --
 *
 *    This procedure is called to find a photo image file format
 *    handler which can parse the image data in the given string.
 *    If a user-specified format string is provided, only handlers
 *    whose names match a prefix of the format string are tried.
 *
 * Results:
 *    A standard TCL return value.  If the return value is TCL_OK, a
 *    pointer to the image format record is returned in
 *    *imageFormatPtr, and the width and height of the image are
 *    returned in *widthPtr and *heightPtr.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static int
MatchStringFormat(interp, string, formatString, imageFormatPtr,
      widthPtr, heightPtr)
    Tcl_Interp *interp;       /* Interpreter to use for reporting errors. */
    char *string;       /* String containing the image data. */
    char *formatString;       /* User-specified format string, or NULL. */
    Tk_PhotoImageFormat **imageFormatPtr;
                        /* A pointer to the photo image format
                         * record is returned here. */
    int *widthPtr, *heightPtr;      /* The dimensions of the image are
                         * returned here. */
{
    int matched;
    Tk_PhotoImageFormat *formatPtr;

    /*
     * Scan through the table of file format handlers to find
     * one which can handle the image.
     */

    matched = 0;
    for (formatPtr = formatList; formatPtr != NULL;
          formatPtr = formatPtr->nextPtr) {
      if (formatString != NULL) {
          if (strncasecmp(formatString, formatPtr->name,
                strlen(formatPtr->name)) != 0) {
            continue;
          }
          matched = 1;
          if (formatPtr->stringMatchProc == NULL) {
            Tcl_AppendResult(interp, "-data option isn't supported for ",
                  formatString, " images", (char *) NULL);
            return TCL_ERROR;
          }
      }
      if ((formatPtr->stringMatchProc != NULL)
            && (*formatPtr->stringMatchProc)(string, formatString,
            widthPtr, heightPtr)) {
          break;
      }
    }

    if (formatPtr == NULL) {
      if ((formatString != NULL) && !matched) {
          Tcl_AppendResult(interp, "image format \"", formatString,
                "\" is not supported", (char *) NULL);
      } else {
          Tcl_AppendResult(interp, "couldn't recognize image data",
                (char *) NULL);
      }
      return TCL_ERROR;
    }

    *imageFormatPtr = formatPtr;
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_FindPhoto --
 *
 *    This procedure is called to get an opaque handle (actually a
 *    PhotoMaster *) for a given image, which can be used in
 *    subsequent calls to Tk_PhotoPutBlock, etc.  The `name'
 *    parameter is the name of the image.
 *
 * Results:
 *    The handle for the photo image, or NULL if there is no
 *    photo image with the name given.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

Tk_PhotoHandle
Tk_FindPhoto(interp, imageName)
    Tcl_Interp *interp;       /* Interpreter (application) in which image
                         * exists. */
    char *imageName;          /* Name of the desired photo image. */
{
    ClientData clientData;
    Tk_ImageType *typePtr;

    clientData = Tk_GetImageMasterData(interp, imageName, &typePtr);
    if (typePtr != &tkPhotoImageType) {
      return NULL;
    }
    return (Tk_PhotoHandle) clientData;
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_PhotoPutBlock --
 *
 *    This procedure is called to put image data into a photo image.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The image data is stored.  The image may be expanded.
 *    The Tk image code is informed that the image has changed.
 *
 *---------------------------------------------------------------------- */

void
Tk_PhotoPutBlock(handle, blockPtr, x, y, width, height)
    Tk_PhotoHandle handle;    /* Opaque handle for the photo image
                         * to be updated. */
    register Tk_PhotoImageBlock *blockPtr;
                        /* Pointer to a structure describing the
                         * pixel data to be copied into the image. */
    int x, y;                 /* Coordinates of the top-left pixel to
                         * be updated in the image. */
    int width, height;        /* Dimensions of the area of the image
                         * to be updated. */
{
    register PhotoMaster *masterPtr;
    int xEnd, yEnd;
    int greenOffset, blueOffset;
    int wLeft, hLeft;
    int wCopy, hCopy;
    unsigned char *srcPtr, *srcLinePtr;
    unsigned char *destPtr, *destLinePtr;
    int pitch;
    XRectangle rect;

    masterPtr = (PhotoMaster *) handle;

    if ((masterPtr->userWidth != 0) && ((x + width) > masterPtr->userWidth)) {
      width = masterPtr->userWidth - x;
    }
    if ((masterPtr->userHeight != 0)
          && ((y + height) > masterPtr->userHeight)) {
      height = masterPtr->userHeight - y;
    }
    if ((width <= 0) || (height <= 0))
      return;

    xEnd = x + width;
    yEnd = y + height;
    if ((xEnd > masterPtr->width) || (yEnd > masterPtr->height)) {
      ImgPhotoSetSize(masterPtr, MAX(xEnd, masterPtr->width),
            MAX(yEnd, masterPtr->height));
    }

    if ((y < masterPtr->ditherY) || ((y == masterPtr->ditherY)
          && (x < masterPtr->ditherX))) {
      /*
       * The dithering isn't correct past the start of this block.
       */
      masterPtr->ditherX = x;
      masterPtr->ditherY = y;
    }

    /*
     * If this image block could have different red, green and blue
     * components, mark it as a color image.
     */

    greenOffset = blockPtr->offset[1] - blockPtr->offset[0];
    blueOffset = blockPtr->offset[2] - blockPtr->offset[0];
    if ((greenOffset != 0) || (blueOffset != 0)) {
      masterPtr->flags |= COLOR_IMAGE;
    }

    /*
     * Copy the data into our local 24-bit/pixel array.
     * If we can do it with a single memcpy, we do.
     */

    destLinePtr = masterPtr->pix24 + (y * masterPtr->width + x) * 3;
    pitch = masterPtr->width * 3;

    if ((blockPtr->pixelSize == 3) && (greenOffset == 1) && (blueOffset == 2)
          && (width <= blockPtr->width) && (height <= blockPtr->height)
          && ((height == 1) || ((x == 0) && (width == masterPtr->width)
            && (blockPtr->pitch == pitch)))) {
      memcpy((VOID *) destLinePtr,
            (VOID *) (blockPtr->pixelPtr + blockPtr->offset[0]),
            (size_t) (height * width * 3));
    } else {
      for (hLeft = height; hLeft > 0;) {
          srcLinePtr = blockPtr->pixelPtr + blockPtr->offset[0];
          hCopy = MIN(hLeft, blockPtr->height);
          hLeft -= hCopy;
          for (; hCopy > 0; --hCopy) {
            destPtr = destLinePtr;
            for (wLeft = width; wLeft > 0;) {
                wCopy = MIN(wLeft, blockPtr->width);
                wLeft -= wCopy;
                srcPtr = srcLinePtr;
                for (; wCopy > 0; --wCopy) {
                  *destPtr++ = srcPtr[0];
                  *destPtr++ = srcPtr[greenOffset];
                  *destPtr++ = srcPtr[blueOffset];
                  srcPtr += blockPtr->pixelSize;
                }
            }
            srcLinePtr += blockPtr->pitch;
            destLinePtr += pitch;
          }
      }
    }

    /*
     * Add this new block to the region which specifies which data is valid.
     */

    rect.x = x;
    rect.y = y;
    rect.width = width;
    rect.height = height;
    TkUnionRectWithRegion(&rect, masterPtr->validRegion,
          masterPtr->validRegion);

    /*
     * Update each instance.
     */

    Dither(masterPtr, x, y, width, height);

    /*
     * Tell the core image code that this image has changed.
     */

    Tk_ImageChanged(masterPtr->tkMaster, x, y, width, height, masterPtr->width,
          masterPtr->height);
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_PhotoPutZoomedBlock --
 *
 *    This procedure is called to put image data into a photo image,
 *    with possible subsampling and/or zooming of the pixels.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The image data is stored.  The image may be expanded.
 *    The Tk image code is informed that the image has changed.
 *
 *----------------------------------------------------------------------
 */

void
Tk_PhotoPutZoomedBlock(handle, blockPtr, x, y, width, height, zoomX, zoomY,
      subsampleX, subsampleY)
    Tk_PhotoHandle handle;    /* Opaque handle for the photo image
                         * to be updated. */
    register Tk_PhotoImageBlock *blockPtr;
                        /* Pointer to a structure describing the
                         * pixel data to be copied into the image. */
    int x, y;                 /* Coordinates of the top-left pixel to
                         * be updated in the image. */
    int width, height;        /* Dimensions of the area of the image
                         * to be updated. */
    int zoomX, zoomY;         /* Zoom factors for the X and Y axes. */
    int subsampleX, subsampleY;     /* Subsampling factors for the X and Y axes. */
{
    register PhotoMaster *masterPtr;
    int xEnd, yEnd;
    int greenOffset, blueOffset;
    int wLeft, hLeft;
    int wCopy, hCopy;
    int blockWid, blockHt;
    unsigned char *srcPtr, *srcLinePtr, *srcOrigPtr;
    unsigned char *destPtr, *destLinePtr;
    int pitch;
    int xRepeat, yRepeat;
    int blockXSkip, blockYSkip;
    XRectangle rect;

    if ((zoomX == 1) && (zoomY == 1) && (subsampleX == 1)
          && (subsampleY == 1)) {
      Tk_PhotoPutBlock(handle, blockPtr, x, y, width, height);
      return;
    }

    masterPtr = (PhotoMaster *) handle;

    if ((zoomX <= 0) || (zoomY <= 0))
      return;
    if ((masterPtr->userWidth != 0) && ((x + width) > masterPtr->userWidth)) {
      width = masterPtr->userWidth - x;
    }
    if ((masterPtr->userHeight != 0)
          && ((y + height) > masterPtr->userHeight)) {
      height = masterPtr->userHeight - y;
    }
    if ((width <= 0) || (height <= 0))
      return;

    xEnd = x + width;
    yEnd = y + height;
    if ((xEnd > masterPtr->width) || (yEnd > masterPtr->height)) {
      int sameSrc = (blockPtr->pixelPtr == masterPtr->pix24);
      ImgPhotoSetSize(masterPtr, MAX(xEnd, masterPtr->width),
            MAX(yEnd, masterPtr->height));
      if (sameSrc) {
          blockPtr->pixelPtr = masterPtr->pix24;
      }
    }

    if ((y < masterPtr->ditherY) || ((y == masterPtr->ditherY)
         && (x < masterPtr->ditherX))) {
      /*
       * The dithering isn't correct past the start of this block.
       */

      masterPtr->ditherX = x;
      masterPtr->ditherY = y;
    }

    /*
     * If this image block could have different red, green and blue
     * components, mark it as a color image.
     */

    greenOffset = blockPtr->offset[1] - blockPtr->offset[0];
    blueOffset = blockPtr->offset[2] - blockPtr->offset[0];
    if ((greenOffset != 0) || (blueOffset != 0)) {
      masterPtr->flags |= COLOR_IMAGE;
    }

    /*
     * Work out what area the pixel data in the block expands to after
     * subsampling and zooming.
     */

    blockXSkip = subsampleX * blockPtr->pixelSize;
    blockYSkip = subsampleY * blockPtr->pitch;
    if (subsampleX > 0)
      blockWid = ((blockPtr->width + subsampleX - 1) / subsampleX) * zoomX;
    else if (subsampleX == 0)
      blockWid = width;
    else
      blockWid = ((blockPtr->width - subsampleX - 1) / -subsampleX) * zoomX;
    if (subsampleY > 0)
      blockHt = ((blockPtr->height + subsampleY - 1) / subsampleY) * zoomY;
    else if (subsampleY == 0)
      blockHt = height;
    else
      blockHt = ((blockPtr->height - subsampleY - 1) / -subsampleY) * zoomY;

    /*
     * Copy the data into our local 24-bit/pixel array.
     */

    destLinePtr = masterPtr->pix24 + (y * masterPtr->width + x) * 3;
    srcOrigPtr = blockPtr->pixelPtr + blockPtr->offset[0];
    if (subsampleX < 0) {
      srcOrigPtr += (blockPtr->width - 1) * blockPtr->pixelSize;
    }
    if (subsampleY < 0) {
      srcOrigPtr += (blockPtr->height - 1) * blockPtr->pitch;
    }

    pitch = masterPtr->width * 3;
    for (hLeft = height; hLeft > 0; ) {
      hCopy = MIN(hLeft, blockHt);
      hLeft -= hCopy;
      yRepeat = zoomY;
      srcLinePtr = srcOrigPtr;
      for (; hCopy > 0; --hCopy) {
          destPtr = destLinePtr;
          for (wLeft = width; wLeft > 0;) {
            wCopy = MIN(wLeft, blockWid);
            wLeft -= wCopy;
            srcPtr = srcLinePtr;
            for (; wCopy > 0; wCopy -= zoomX) {
                for (xRepeat = MIN(wCopy, zoomX); xRepeat > 0; xRepeat--) {
                  *destPtr++ = srcPtr[0];
                  *destPtr++ = srcPtr[greenOffset];
                  *destPtr++ = srcPtr[blueOffset];
                }
                srcPtr += blockXSkip;
            }
          }
          destLinePtr += pitch;
          yRepeat--;
          if (yRepeat <= 0) {
            srcLinePtr += blockYSkip;
            yRepeat = zoomY;
          }
      }
    }

    /*
     * Add this new block to the region that specifies which data is valid.
     */

    rect.x = x;
    rect.y = y;
    rect.width = width;
    rect.height = height;
    TkUnionRectWithRegion(&rect, masterPtr->validRegion,
          masterPtr->validRegion);

    /*
     * Update each instance.
     */

    Dither(masterPtr, x, y, width, height);

    /*
     * Tell the core image code that this image has changed.
     */

    Tk_ImageChanged(masterPtr->tkMaster, x, y, width, height, masterPtr->width,
          masterPtr->height);
}

/*
 *----------------------------------------------------------------------
 *
 * Dither --
 *
 *    This procedure is called to update an area of each instance's
 *    pixmap by dithering the corresponding area of the image master.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The pixmap of each instance of this image gets updated.
 *    The fields in *masterPtr indicating which area of the image
 *    is correctly dithered get updated.
 *
 *----------------------------------------------------------------------
 */

static void
Dither(masterPtr, x, y, width, height)
    PhotoMaster *masterPtr;   /* Image master whose instances are
                         * to be updated. */
    int x, y;                 /* Coordinates of the top-left pixel
                         * in the area to be dithered. */
    int width, height;        /* Dimensions of the area to be dithered. */
{
    PhotoInstance *instancePtr;

    if ((width <= 0) || (height <= 0)) {
      return;
    }

    for (instancePtr = masterPtr->instancePtr; instancePtr != NULL;
          instancePtr = instancePtr->nextPtr) {
      DitherInstance(instancePtr, x, y, width, height);
    }

    /*
     * Work out whether this block will be correctly dithered
     * and whether it will extend the correctly dithered region.
     */

    if (((y < masterPtr->ditherY)
          || ((y == masterPtr->ditherY) && (x <= masterPtr->ditherX)))
          && ((y + height) > (masterPtr->ditherY))) {

      /*
       * This block starts inside (or immediately after) the correctly
       * dithered region, so the first scan line at least will be right.
       * Furthermore this block extends into scanline masterPtr->ditherY.
       */

      if ((x == 0) && (width == masterPtr->width)) {
          /*
           * We are doing the full width, therefore the dithering
           * will be correct to the end.
           */

          masterPtr->ditherX = 0;
          masterPtr->ditherY = y + height;
      } else {
          /*
           * We are doing partial scanlines, therefore the
           * correctly-dithered region will be extended by
           * at most one scan line.
           */

          if (x <= masterPtr->ditherX) {
            masterPtr->ditherX = x + width;
            if (masterPtr->ditherX >= masterPtr->width) {
                masterPtr->ditherX = 0;
                masterPtr->ditherY++;
            }
          }
      }
    }

}    

/*
 *----------------------------------------------------------------------
 *
 * DitherInstance --
 *
 *    This procedure is called to update an area of an instance's
 *    pixmap by dithering the corresponding area of the master.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The instance's pixmap gets updated.
 *
 *----------------------------------------------------------------------
 */

static void
DitherInstance(instancePtr, xStart, yStart, width, height)
    PhotoInstance *instancePtr;     /* The instance to be updated. */
    int xStart, yStart;       /* Coordinates of the top-left pixel in the
                         * block to be dithered. */
    int width, height;        /* Dimensions of the block to be dithered. */
{
    PhotoMaster *masterPtr;
    ColorTable *colorPtr;
    XImage *imagePtr;
    int nLines, bigEndian;
    int i, c, x, y;
    int xEnd, yEnd;
    int bitsPerPixel, bytesPerLine, lineLength;
    unsigned char *srcLinePtr, *srcPtr;
    schar *errLinePtr, *errPtr;
    unsigned char *destBytePtr, *dstLinePtr;
    pixel *destLongPtr;
    pixel firstBit, word, mask;
    int col[3];
    int doDithering = 1;

    colorPtr = instancePtr->colorTablePtr;
    masterPtr = instancePtr->masterPtr;

    /*
     * Turn dithering off in certain cases where it is not
     * needed (TrueColor, DirectColor with many colors).
     */

    if ((colorPtr->visualInfo.class == DirectColor)
          || (colorPtr->visualInfo.class == TrueColor)) {
      int nRed, nGreen, nBlue, result;

      result = sscanf(colorPtr->id.palette, "%d/%d/%d", &nRed,
            &nGreen, &nBlue);
      if ((nRed >= 256)
            && ((result == 1) || ((nGreen >= 256) && (nBlue >= 256)))) {
          doDithering = 0;
      }
    }

    /*
     * First work out how many lines to do at a time,
     * then how many bytes we'll need for pixel storage,
     * and allocate it.
     */

    nLines = (MAX_PIXELS + width - 1) / width;
    if (nLines < 1) {
      nLines = 1;
    }
    if (nLines > height ) {
      nLines = height;
    }

    imagePtr = instancePtr->imagePtr;
    if (imagePtr == NULL) {
      return;                 /* we must be really tight on memory */
    }
    bitsPerPixel = imagePtr->bits_per_pixel;
    bytesPerLine = ((bitsPerPixel * width + 31) >> 3) & ~3;
    imagePtr->width = width;
    imagePtr->height = nLines;
    imagePtr->bytes_per_line = bytesPerLine;
    imagePtr->data = (char *) ckalloc((unsigned) (imagePtr->bytes_per_line * nLines));
    bigEndian = imagePtr->bitmap_bit_order == MSBFirst;
    firstBit = bigEndian? (1 << (imagePtr->bitmap_unit - 1)): 1;

    lineLength = masterPtr->width * 3;
    srcLinePtr = masterPtr->pix24 + yStart * lineLength + xStart * 3;
    errLinePtr = instancePtr->error + yStart * lineLength + xStart * 3;
    xEnd = xStart + width;

    /*
     * Loop over the image, doing at most nLines lines before
     * updating the screen image.
     */

    for (; height > 0; height -= nLines) {
      if (nLines > height) {
          nLines = height;
      }
      dstLinePtr = (unsigned char *) imagePtr->data;
      yEnd = yStart + nLines;
      for (y = yStart; y < yEnd; ++y) {
          srcPtr = srcLinePtr;
          errPtr = errLinePtr;
          destBytePtr = dstLinePtr;
          destLongPtr = (pixel *) dstLinePtr;
          if (colorPtr->flags & COLOR_WINDOW) {
            /*
             * Color window.  We dither the three components
             * independently, using Floyd-Steinberg dithering,
             * which propagates errors from the quantization of
             * pixels to the pixels below and to the right.
             */

            for (x = xStart; x < xEnd; ++x) {
                if (doDithering) {
                  for (i = 0; i < 3; ++i) {
                      /*
                       * Compute the error propagated into this pixel
                       * for this component.
                       * If e[x,y] is the array of quantization error
                       * values, we compute
                       *     7/16 * e[x-1,y] + 1/16 * e[x-1,y-1]
                       *   + 5/16 * e[x,y-1] + 3/16 * e[x+1,y-1]
                       * and round it to an integer.
                       *
                       * The expression ((c + 2056) >> 4) - 128
                       * computes round(c / 16), and works correctly on
                       * machines without a sign-extending right shift.
                       */
                      
                      c = (x > 0) ? errPtr[-3] * 7: 0;
                      if (y > 0) {
                        if (x > 0) {
                            c += errPtr[-lineLength-3];
                        }
                        c += errPtr[-lineLength] * 5;
                        if ((x + 1) < masterPtr->width) {
                            c += errPtr[-lineLength+3] * 3;
                        }
                      }
                      
                      /*
                       * Add the propagated error to the value of this
                       * component, quantize it, and store the
                       * quantization error.
                       */
                      
                      c = ((c + 2056) >> 4) - 128 + *srcPtr++;
                      if (c < 0) {
                        c = 0;
                      } else if (c > 255) {
                        c = 255;
                      }
                      col[i] = colorPtr->colorQuant[i][c];
                      *errPtr++ = c - col[i];
                  }
                } else {
                  /* 
                   * Output is virtually continuous in this case,
                   * so don't bother dithering.
                   */

                  col[0] = *srcPtr++;
                  col[1] = *srcPtr++;
                  col[2] = *srcPtr++;
                }

                /*
                 * Translate the quantized component values into
                 * an X pixel value, and store it in the image.
                 */

                i = colorPtr->redValues[col[0]]
                      + colorPtr->greenValues[col[1]]
                      + colorPtr->blueValues[col[2]];
                if (colorPtr->flags & MAP_COLORS) {
                  i = colorPtr->pixelMap[i];
                }
                switch (bitsPerPixel) {
                  case NBBY:
                      *destBytePtr++ = i;
                      break;
#ifndef __WIN32__
/*
 * This case is not valid for Windows because the image format is different
 * from the pixel format in Win32.  Eventually we need to fix the image
 * code in Tk to use the Windows native image ordering.  This would speed
 * up the image code for all of the common sizes.
 */

                  case NBBY * sizeof(pixel):
                      *destLongPtr++ = i;
                      break;
#endif
                  default:
                      XPutPixel(imagePtr, x - xStart, y - yStart,
                            (unsigned) i);
                }
            }

          } else if (bitsPerPixel > 1) {
            /*
             * Multibit monochrome window.  The operation here is similar
             * to the color window case above, except that there is only
             * one component.  If the master image is in color, use the
             * luminance computed as
             *    0.344 * red + 0.5 * green + 0.156 * blue.
             */

            for (x = xStart; x < xEnd; ++x) {
                c = (x > 0) ? errPtr[-1] * 7: 0;
                if (y > 0) {
                  if (x > 0)  {
                      c += errPtr[-lineLength-1];
                  }
                  c += errPtr[-lineLength] * 5;
                  if (x + 1 < masterPtr->width) {
                      c += errPtr[-lineLength+1] * 3;
                  }
                }
                c = ((c + 2056) >> 4) - 128;

                if ((masterPtr->flags & COLOR_IMAGE) == 0) {
                  c += srcPtr[0];
                } else {
                  c += (unsigned)(srcPtr[0] * 11 + srcPtr[1] * 16
                              + srcPtr[2] * 5 + 16) >> 5;
                }
                srcPtr += 3;

                if (c < 0) {
                  c = 0;
                } else if (c > 255) {
                  c = 255;
                }
                i = colorPtr->colorQuant[0][c];
                *errPtr++ = c - i;
                i = colorPtr->redValues[i];
                switch (bitsPerPixel) {
                  case NBBY:
                      *destBytePtr++ = i;
                      break;
#ifndef __WIN32__
/*
 * This case is not valid for Windows because the image format is different
 * from the pixel format in Win32.  Eventually we need to fix the image
 * code in Tk to use the Windows native image ordering.  This would speed
 * up the image code for all of the common sizes.
 */

                  case NBBY * sizeof(pixel):
                      *destLongPtr++ = i;
                      break;
#endif
                  default:
                      XPutPixel(imagePtr, x - xStart, y - yStart,
                            (unsigned) i);
                }
            }
          } else {
            /*
             * 1-bit monochrome window.  This is similar to the
             * multibit monochrome case above, except that the
             * quantization is simpler (we only have black = 0
             * and white = 255), and we produce an XY-Bitmap.
             */

            word = 0;
            mask = firstBit;
            for (x = xStart; x < xEnd; ++x) {
                /*
                 * If we have accumulated a whole word, store it
                 * in the image and start a new word.
                 */

                if (mask == 0) {
                  *destLongPtr++ = word;
                  mask = firstBit;
                  word = 0;
                }

                c = (x > 0) ? errPtr[-1] * 7: 0;
                if (y > 0) {
                  if (x > 0) {
                      c += errPtr[-lineLength-1];
                  }
                  c += errPtr[-lineLength] * 5;
                  if (x + 1 < masterPtr->width) {
                      c += errPtr[-lineLength+1] * 3;
                  }
                }
                c = ((c + 2056) >> 4) - 128;

                if ((masterPtr->flags & COLOR_IMAGE) == 0) {
                  c += srcPtr[0];
                } else {
                  c += (unsigned)(srcPtr[0] * 11 + srcPtr[1] * 16
                              + srcPtr[2] * 5 + 16) >> 5;
                }
                srcPtr += 3;

                if (c < 0) {
                  c = 0;
                } else if (c > 255) {
                  c = 255;
                }
                if (c >= 128) {
                  word |= mask;
                  *errPtr++ = c - 255;
                } else {
                  *errPtr++ = c;
                }
                mask = bigEndian? (mask >> 1): (mask << 1);
            }
            *destLongPtr = word;
          }
          srcLinePtr += lineLength;
          errLinePtr += lineLength;
          dstLinePtr += bytesPerLine;
      }

      /*
       * Update the pixmap for this instance with the block of
       * pixels that we have just computed.
       */

      TkPutImage(colorPtr->pixelMap, colorPtr->numColors,
            instancePtr->display, instancePtr->pixels,
            instancePtr->gc, imagePtr, 0, 0, xStart, yStart,
            (unsigned) width, (unsigned) nLines);
      yStart = yEnd;
      
    }

    ckfree(imagePtr->data);
    imagePtr->data = NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_PhotoBlank --
 *
 *    This procedure is called to clear an entire photo image.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The valid region for the image is set to the null region.
 *    The generic image code is notified that the image has changed.
 *
 *----------------------------------------------------------------------
 */

void
Tk_PhotoBlank(handle)
    Tk_PhotoHandle handle;    /* Handle for the image to be blanked. */
{
    PhotoMaster *masterPtr;
    PhotoInstance *instancePtr;

    masterPtr = (PhotoMaster *) handle;
    masterPtr->ditherX = masterPtr->ditherY = 0;
    masterPtr->flags = 0;

    /*
     * The image has valid data nowhere.
     */

    if (masterPtr->validRegion != NULL) {
      TkDestroyRegion(masterPtr->validRegion);
    }
    masterPtr->validRegion = TkCreateRegion();

    /*
     * Clear out the 24-bit pixel storage array.
     * Clear out the dithering error arrays for each instance.
     */

    memset((VOID *) masterPtr->pix24, 0,
          (size_t) (masterPtr->width * masterPtr->height * 3));
    for (instancePtr = masterPtr->instancePtr; instancePtr != NULL;
          instancePtr = instancePtr->nextPtr) {
      if (instancePtr->error) {
          memset((VOID *) instancePtr->error, 0,
                (size_t) (masterPtr->width * masterPtr->height
                * 3 * sizeof(schar)));
      }
    }

    /*
     * Tell the core image code that this image has changed.
     */

    Tk_ImageChanged(masterPtr->tkMaster, 0, 0, masterPtr->width,
          masterPtr->height, masterPtr->width, masterPtr->height);
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_PhotoExpand --
 *
 *    This procedure is called to request that a photo image be
 *    expanded if necessary to be at least `width' pixels wide and
 *    `height' pixels high.  If the user has declared a definite
 *    image size (using the -width and -height configuration
 *    options) then this call has no effect.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The size of the photo image may change; if so the generic
 *    image code is informed.
 *
 *----------------------------------------------------------------------
 */

void
Tk_PhotoExpand(handle, width, height)
    Tk_PhotoHandle handle;    /* Handle for the image to be expanded. */
    int width, height;        /* Desired minimum dimensions of the image. */
{
    PhotoMaster *masterPtr;

    masterPtr = (PhotoMaster *) handle;

    if (width <= masterPtr->width) {
      width = masterPtr->width;
    }
    if (height <= masterPtr->height) {
      height = masterPtr->height;
    }
    if ((width != masterPtr->width) || (height != masterPtr->height)) {
      ImgPhotoSetSize(masterPtr, MAX(width, masterPtr->width),
            MAX(height, masterPtr->height));
      Tk_ImageChanged(masterPtr->tkMaster, 0, 0, 0, 0, masterPtr->width,
            masterPtr->height);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_PhotoGetSize --
 *
 *    This procedure is called to obtain the current size of a photo
 *    image.
 *
 * Results:
 *    The image's width and height are returned in *widthp
 *    and *heightp.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
Tk_PhotoGetSize(handle, widthPtr, heightPtr)
    Tk_PhotoHandle handle;    /* Handle for the image whose dimensions
                         * are requested. */
    int *widthPtr, *heightPtr;      /* The dimensions of the image are returned
                         * here. */
{
    PhotoMaster *masterPtr;

    masterPtr = (PhotoMaster *) handle;
    *widthPtr = masterPtr->width;
    *heightPtr = masterPtr->height;
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_PhotoSetSize --
 *
 *    This procedure is called to set size of a photo image.
 *    This call is equivalent to using the -width and -height
 *    configuration options.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The size of the image may change; if so the generic
 *    image code is informed.
 *
 *----------------------------------------------------------------------
 */

void
Tk_PhotoSetSize(handle, width, height)
    Tk_PhotoHandle handle;    /* Handle for the image whose size is to
                         * be set. */
    int width, height;        /* New dimensions for the image. */
{
    PhotoMaster *masterPtr;

    masterPtr = (PhotoMaster *) handle;

    masterPtr->userWidth = width;
    masterPtr->userHeight = height;
    ImgPhotoSetSize(masterPtr, ((width > 0) ? width: masterPtr->width),
          ((height > 0) ? height: masterPtr->height));
    Tk_ImageChanged(masterPtr->tkMaster, 0, 0, 0, 0,
          masterPtr->width, masterPtr->height);
}

/*
 *----------------------------------------------------------------------
 *
 * Tk_PhotoGetImage --
 *
 *    This procedure is called to obtain image data from a photo
 *    image.  This procedure fills in the Tk_PhotoImageBlock structure
 *    pointed to by `blockPtr' with details of the address and
 *    layout of the image data in memory.
 *
 * Results:
 *    TRUE (1) indicating that image data is available,
 *    for backwards compatibility with the old photo widget.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

int
Tk_PhotoGetImage(handle, blockPtr)
    Tk_PhotoHandle handle;    /* Handle for the photo image from which
                         * image data is desired. */
    Tk_PhotoImageBlock *blockPtr;
                        /* Information about the address and layout
                         * of the image data is returned here. */
{
    PhotoMaster *masterPtr;

    masterPtr = (PhotoMaster *) handle;
    blockPtr->pixelPtr = masterPtr->pix24;
    blockPtr->width = masterPtr->width;
    blockPtr->height = masterPtr->height;
    blockPtr->pitch = masterPtr->width * 3;
    blockPtr->pixelSize = 3;
    blockPtr->offset[0] = 0;
    blockPtr->offset[1] = 1;
    blockPtr->offset[2] = 2;
    return 1;
}

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