/* STARTHEADER
 *
 * File :       tga.c
 *
 * Author :     Paul Obermeier (paul@poSoft.de)
 *
 * Date :       2000 / 11 / 22
 *
 * Copyright :  (C) 2000-2019 Paul Obermeier
 *
 * Description :
 *
 * A photo image handler for Truevision's TARGA file format.
 *
 * The following image types are supported:
 *
 * 24-bit pixels: True-color (RGB, each channel 8 bit).
 * 32-bit pixels: True-color with alpha channel (RGBA, each channel 8 bit).
 *
 * List of currently supported features:
 *
 * Type   |     Read      |     Write     |
 *        | -file | -data | -file | -data |
 * ----------------------------------------
 * 24-bit | Yes   | Yes   | Yes   | Yes   |
 * 32-bit | Yes   | Yes   | Yes   | Yes   |
 *
 * All images types may be either uncompressed (Targa-Type 2) or
 * run-length encoded (Targa-Type 10).
 *
 *
 * The following format options are available:
 *
 * Read  TGA image: "tga -matte <bool> -verbose <bool>"
 * Write TGA image: "tga -matte <bool> -verbose <bool> -compression <type>"
 *
 * -matte <bool>:       If set to false, a matte (alpha) channel is ignored
 *                      during reading or writing. Default is true.
 * -verbose <bool>:     If set to true, additional information about the file
 *                      format is printed to stdout. Default is false.
 * -compression <type>: Set the compression mode to either "none" or "rle".
 *                      Default is "rle".
 *
 * Notes:
 *
 * - As Targa files do not have a "magic number" somewhere in the file header,
 *   it is difficult to automatically recognize this format.
 *   Therefore it should be specified as one of the first entries in the list of
 *   package require tkimg::*.
 *
 * ENDHEADER
 *
 */

/*
 * Generic initialization code, parameterized via CPACKAGE and PACKAGE.
 */

#include "init.c"


/* #define DEBUG_LOCAL */

/* Some defines and typedefs. */
#define TRUE  1
#define FALSE 0
typedef unsigned char Boln;     /* Boolean value: TRUE or FALSE */
typedef unsigned char UByte;    /* Unsigned  8 bit integer */
typedef char  Byte;             /* Signed    8 bit integer */
typedef short Short;            /* Signed   16 bit integer */
typedef int Int;                /* Signed   32 bit integer */

/* Supported TARGA version numbers */
#define TGA_RGB_UNCOMP   2
#define TGA_RGB_COMP    10

/* Macros needed for run-length encoding. */
#define TGA_MODE_SAME   0
#define TGA_MODE_DIFF   1
#define MINRUN   3
#define MAXRUN 127

/* Macros for acessing header fields */
#define ENC_LEFT_RIGHT(imgdes) (((imgdes >> 4) & 0x1)? FALSE: TRUE)
#define ENC_TOP_BOTTOM(imgdes) (((imgdes >> 5) & 0x1)? TRUE: FALSE)
#define NCHAN(pixsize)         ((pixsize == 24) ? 3: 4)
#define IS_COMPRESSED(imgtyp)  ((imgtyp == TGA_RGB_COMP)? TRUE: FALSE)

/* The Targa header structure */
typedef struct {
    UByte numid;
    UByte maptyp;
    UByte imgtyp;
    Short maporig;
    Short mapsize;
    UByte mapbits;
    Short xorig;
    Short yorig;
    Short xsize;
    Short ysize;
    UByte pixsize;
    UByte imgdes;
} TGAHEADER;

/* Structure to hold information about the Targa file being processed. */
typedef struct {
    TGAHEADER th;
    Int   scanrest,     /* Number of pixels belonging to next scanline */
          scanmode;     /* Current compression mode */
    UByte *red,         /* Pointers to step through scanlines */
          *green,
          *blue,
          *matte;
    UByte *redScan,     /* Buffer for one scanline: Red   channel */
          *greenScan,   /* Buffer for one scanline: Green channel */
          *blueScan,    /* Buffer for one scanline: Blue  channel */
          *matteScan;   /* Buffer for one scanline: Matte channel */
    UByte *pixbuf;
#ifdef DEBUG_LOCAL
        Int total;
#endif
} TGAFILE;

/* Format options structure for use with ParseFormatOpts */
typedef struct {
    Int   compression;
    Boln  verbose;
    Boln  matte;
} FMTOPT;

static void tgaClose(TGAFILE *tf)
{
    if (tf->redScan)   ckfree((char *)tf->redScan);
    if (tf->greenScan) ckfree((char *)tf->greenScan);
    if (tf->blueScan)  ckfree((char *)tf->blueScan);
    if (tf->matteScan) ckfree((char *)tf->matteScan);
    if (tf->pixbuf)    ckfree((char *)tf->pixbuf);
    return;
}

static Boln readError(Tcl_Interp *interp)
{
    Tcl_AppendResult(interp, "Unexpected end of file", (char *) NULL);
    return FALSE;
}

/* Read 1 byte, representing an unsigned integer number. */

static Boln readUByte (tkimg_MFile *handle, UByte *b)
{
    char buf[1];
    if (1 != tkimg_Read2(handle, buf, 1)) {
        return FALSE;
    }
    *b = buf[0];
    return TRUE;
}

/* Read 2 bytes, representing a short integer in the form <LowByte, HighByte>,
   from a file and convert them into the current machine's format. */

static Boln readShort (tkimg_MFile *handle, Short *s)
{
    char buf[2];
    if (2 != tkimg_Read2(handle, buf, 2)) {
        return FALSE;
    }
    *s = (buf[0] & 0xFF) | (buf[1] << 8);
    return TRUE;
}

/* Write a byte, representing an unsigned integer to a file. */

static Boln writeUByte (tkimg_MFile *handle, UByte b)
{
    UByte buf[1];
    buf[0] = b;
    if (1 != tkimg_Write2(handle, (const char *)buf, 1)) {
        return FALSE;
    }
    return TRUE;
}

/* Write a byte, representing a signed integer to a file. */

static Boln writeByte(tkimg_MFile *handle, Byte b)
{
    Byte buf[1];
    buf[0] = b;
    if (1 != tkimg_Write2(handle, buf, 1)) {
        return FALSE;
    }
    return TRUE;
}

/* Convert a short integer number into the format <LowByte, HighByte> (an array
   of 2 bytes) and write the array to a file. */

static Boln writeShort (tkimg_MFile *handle, Short s)
{
    Byte buf[2];
    buf[0] = s;
    buf[1] = s >> 8;
    if (2 != tkimg_Write2(handle, buf, 2)) {
        return FALSE;
    }
    return TRUE;
}

#define OUT Tcl_WriteChars (outChan, str, -1)
static void printImgInfo (TGAHEADER *th, const char *filename, const char *msg)
{
    Tcl_Channel outChan;
    char str[256];

    outChan = Tcl_GetStdChannel (TCL_STDOUT);
    if (!outChan) {
        return;
    }

    sprintf(str, "%s %s\n", msg, filename);                                     OUT;
    sprintf(str, "\tSize in pixel      : %d x %d\n", th->xsize, th->ysize);     OUT;
    sprintf(str, "\tNo. of channels    : %d\n", NCHAN(th->pixsize));            OUT;
    sprintf(str, "\tCompression        : %s\n",
                 IS_COMPRESSED(th->imgtyp)? "rle": "none");                     OUT;
    sprintf(str, "\tVertical encoding  : %s\n",
                 ENC_TOP_BOTTOM(th->imgdes)? "Top -> Bottom": "Bottom -> Top"); OUT;
    sprintf(str, "\tHorizontal encoding: %s\n",
                 ENC_LEFT_RIGHT(th->imgdes)? "Left -> Right": "Right -> Left"); OUT;
    Tcl_Flush(outChan);
}
#undef OUT
static Boln readHeader (tkimg_MFile *handle, TGAHEADER *th)
{
    Int i;
    UByte dummy;

    if (!readUByte (handle, &th->numid) ||
        !readUByte (handle, &th->maptyp) ||
        !readUByte (handle, &th->imgtyp) ||
        !readShort (handle, &th->maporig) ||
        !readShort (handle, &th->mapsize) ||
        !readUByte (handle, &th->mapbits) ||
        !readShort (handle, &th->xorig) ||
        !readShort (handle, &th->yorig) ||
        !readShort (handle, &th->xsize) ||
        !readShort (handle, &th->ysize) ||
        !readUByte (handle, &th->pixsize) ||
        !readUByte (handle, &th->imgdes)) {
        return FALSE;
    }

    /* Try to find out if this file can possibly be a TARGA pixel file. */
    if (!((th->imgtyp == TGA_RGB_UNCOMP || th->imgtyp == TGA_RGB_COMP) &&
          (th->pixsize == 24 || th->pixsize == 32))) {
        return FALSE;
    }

    for ( i=0; i<th->numid; i++) {
        if (!readUByte (handle, &dummy)) {
            return FALSE;
        }
    }

    if (th->xsize < 1 || th->ysize < 1) {
        return FALSE;
    }

    /* Skip colormap data, if present. */
    if (th->mapsize > 0) {
        Int   mapbytes;
        switch (th->mapbits) {
            case 15:
            case 16:
                mapbytes = 2 * th->mapsize;
                break;
            case 24:
                mapbytes = 3 * th->mapsize;
                break;
            case 32:
                mapbytes = 4 * th->mapsize;
                break;
            default:
                return FALSE;
        }
        while (mapbytes--) {
            if (!readUByte (handle, &dummy)) {
                return FALSE;
            }
        }
    }
    return TRUE;
}

static Boln writeHeader(tkimg_MFile *handle, TGAHEADER *th)
{
    if (!writeUByte (handle, th->numid) ||
        !writeUByte (handle, th->maptyp) ||
        !writeUByte (handle, th->imgtyp) ||
        !writeShort (handle, th->maporig) ||
        !writeShort (handle, th->mapsize) ||
        !writeUByte (handle, th->mapbits) ||
        !writeShort (handle, th->xorig) ||
        !writeShort (handle, th->yorig) ||
        !writeShort (handle, th->xsize) ||
        !writeShort (handle, th->ysize) ||
        !writeUByte (handle, th->pixsize) ||
        !writeUByte (handle, th->imgdes)) {
        return FALSE;
    }
    return TRUE;
}

/* A pixel is represented by 3 or 4 bytes in the order Blue/Green/Red/Alpha.
   We are converting the order into standard RGBA order.
   Note that TARGA allows pixel values to be compressed across scanline boundaries.
*/

/* Read the value of a pixel from "handle" and assume it must be repeated "n" times. */

static Boln readRlePixel (Tcl_Interp *interp, tkimg_MFile *handle, UByte **pixBufPtr,
                          Int *countPtr, Int stop, Int n, TGAFILE *tf)
{
    Int i, count, nchan;
    UByte localBuf[4];

    nchan = NCHAN(tf->th.pixsize);
    if (nchan != tkimg_Read2(handle, (char *)localBuf, nchan))
        return readError (interp);
    count = *countPtr;
    for (i=0; i<n; i++) {
#ifdef DEBUG_LOCAL
        tf->total++;
#endif
        (*pixBufPtr)[0] = localBuf[2];
        (*pixBufPtr)[1] = localBuf[1];
        (*pixBufPtr)[2] = localBuf[0];
        if (nchan == 4) {
            (*pixBufPtr)[3] = localBuf[3];
        }
        (*pixBufPtr) += nchan;
        count++;

        if (count == stop) {
            /* Scanline is filled with pixel values.
               Determine the number of pixels to keep for next scanline. */
            tf->scanrest = n - i - 1;
            *countPtr = count;
            return TRUE;
        }
    }
    *countPtr = count;
    return TRUE;
}

/* The channels of scan line number "y" are read. */

static Boln tgaReadScan (Tcl_Interp *interp, tkimg_MFile *handle,
                         TGAFILE *tf, Int y)
{
    Int   nchan;
    Int   count, stop;
    UByte localBuf[4];
    UByte *pixBufPtr;

    count = 0;
    stop  = tf->th.xsize;
    nchan = NCHAN(tf->th.pixsize);
    pixBufPtr = tf->pixbuf;

#ifdef DEBUG_LOCAL
        tf->total = 0;
#endif

    if (IS_COMPRESSED (tf->th.imgtyp)) {
        Byte cbuf[1];
        Int  pix, numpix;
        /* While there are pixels left from the previous scanline,
           either fill the current scanline with the pixel value
           still stored in "pixbuf" (TGA_MODE_SAME) or read in the
           appropriate number of pixel values (TGA_MODE_DIFF). */
        while (tf->scanrest) {
            if (tf->scanmode == TGA_MODE_DIFF) {
                if (nchan != tkimg_Read2(handle, (char *)localBuf, nchan)) {
                    return readError (interp);
                }
            }
#ifdef DEBUG_LOCAL
            tf->total++;
#endif
            *pixBufPtr++ = localBuf[2];
            *pixBufPtr++ = localBuf[1];
            *pixBufPtr++ = localBuf[0];
            if (nchan == 4) {
                *pixBufPtr++ = localBuf[3];
            }
            count++;

            tf->scanrest--;
            /* If the image is small, the compression might go over several
               scanlines. */
            if (count == stop) {
                return TRUE;
            }
        }

        /* Read the byte telling us the compression mode and the compression
           count. Then read the pixel values till a scanline is filled. */
        do {
            if (1 != tkimg_Read2(handle, cbuf, 1)) {
                return readError (interp);
            }
            numpix = (cbuf[0] & 0x7F) + 1;

            if ((cbuf[0] & 0x80) != 0x80) {
                tf->scanmode = TGA_MODE_DIFF;
                for (pix=0; pix<numpix; pix++) {
                    if (!readRlePixel (interp, handle, &pixBufPtr,
                                       &count, stop, 1, tf)) {
                        return FALSE;
                    }
                    if (count == stop) {
                        tf->scanrest = numpix - pix - 1;
                        break;
                    }
                }
            } else {
                tf->scanmode = TGA_MODE_SAME;
                if (!readRlePixel (interp, handle, &pixBufPtr,
                                   &count, stop, numpix, tf)) {
                    return FALSE;
                }
            }
        } while (count < stop);

#ifdef DEBUG_LOCAL
        printf("\tScanline %d: Pixels: %d Rest: %d\n", y, tf->total, tf->scanrest);
#endif
    } else {
        /* Read uncompressed pixel data. */
        Int   i, bytesPerLine;
        UByte curPix;

        bytesPerLine = nchan * tf->th.xsize;
        if (bytesPerLine != tkimg_Read2(handle, (char *)tf->pixbuf, bytesPerLine)) {
            return readError (interp);
        }

        for (i=0; i<stop; i++) {
            curPix = pixBufPtr[2];
            pixBufPtr[2] = pixBufPtr[0];
            pixBufPtr[0] = curPix;
            pixBufPtr += nchan;
        }
    }
    return TRUE;
}

static Boln writePixel(tkimg_MFile *handle, UByte b, UByte g,
                        UByte r, UByte m, Int nchan)
{
    UByte buf[4];
    buf[0] = b;
    buf[1] = g;
    buf[2] = r;
    buf[3] = m;
    if ((size_t)nchan != tkimg_Write2(handle, (const char *)buf, nchan)) {
        return FALSE;
    }
    return TRUE;
}

static Boln tgaWriteScan(Tcl_Interp *interp, tkimg_MFile *handle,
                          TGAFILE *tf, Int y)
{
    UByte *stop, *red_end, *green_end, *blue_end, *matte_end;
    Int nchan;

    tf->red   = tf->redScan;
    tf->green = tf->greenScan;
    tf->blue  = tf->blueScan;
    tf->matte = tf->matteScan;
    stop = tf->red + tf->th.xsize;
    nchan = NCHAN(tf->th.pixsize);

    /* Write the scanline data to the file. */
    if (! IS_COMPRESSED(tf->th.imgtyp)) {
        while (tf->red < stop) {
            if (!writePixel(handle, *tf->blue, *tf->green, *tf->red, *tf->matte, nchan)) {
                return FALSE;
            }
            tf->blue++;
            tf->green++;
            tf->red++;
            tf->matte++;
        }
    } else {
        /* Run-length Compression */
        red_end = tf->red + 1;
        green_end = tf->green + 1;
        blue_end = tf->blue + 1;
        matte_end = tf->matte + 1;
        while (tf->red < stop) {
            while (red_end < stop &&
                   *tf->red == *red_end &&
                   *tf->green == *green_end &&
                   *tf->blue == *blue_end &&
                   red_end - tf->red - 1 < MAXRUN) {
                if (nchan == 4) {
                    if (*tf->matte != *matte_end) {
                        break;
                    }
                }
                red_end++;
                green_end++;
                blue_end++;
                matte_end++;
            }
            if (red_end - tf->red >= MINRUN) {
                /* Found a run of compressable data */
                if (!writeByte(handle, (Byte)(((red_end - tf->red)-1)|0x80)) ||
                    !writePixel(handle, *tf->blue, *tf->green, *tf->red, *tf->matte, nchan)) {
                    return FALSE;
                }
                tf->red   = red_end;
                tf->green = green_end;
                tf->blue  = blue_end;
                tf->matte = matte_end;
            } else {
                /* Found a run of uncompressable data */
                while (red_end < stop &&
                       ((red_end + 1 >= stop ||
                        *red_end != *(red_end + 1)) ||
                        (red_end + 2 >= stop ||
                        *(red_end + 1) != *(red_end + 2))) &&
                       ((green_end + 1 >= stop ||
                        *green_end != *(green_end + 1)) ||
                        (green_end + 2 >= stop ||
                        *(green_end + 1) != *(green_end + 2))) &&
                       ((blue_end + 1 >= stop ||
                        *blue_end != *(blue_end + 1)) ||
                        (blue_end + 2 >= stop ||
                        *(blue_end + 1) != *(blue_end + 2))) &&
                        red_end - tf->red < MAXRUN) {
                    if (nchan == 4) {
                        if (! ((matte_end + 1 >= stop ||
                               *matte_end != *(matte_end + 1)) ||
                               (matte_end + 2 >= stop ||
                               *(matte_end + 1) != *(matte_end + 2)))) {
                            break;
                        }
                    }
                    red_end++;
                    green_end++;
                    blue_end++;
                    matte_end++;
                }
                if (!writeByte(handle, (Byte)((red_end - tf->red) - 1))) {
                    return FALSE;
                }
                while (tf->red < red_end) {
                    if (!writePixel(handle, *tf->blue, *tf->green, *tf->red, *tf->matte, nchan)) {
                        return FALSE;
                    }
                    tf->red++;
                    tf->green++;
                    tf->blue++;
                    tf->matte++;
                }
            }
            red_end++;
            green_end++;
            blue_end++;
            matte_end++;
        }
    }
    return TRUE;
}

/*
 * Here is the start of the standard functions needed for every image format.
 */

/*
 * Prototypes for local procedures defined in this file:
 */

static int ParseFormatOpts(Tcl_Interp *interp, Tcl_Obj *format, FMTOPT *opts);
static int CommonMatch(tkimg_MFile *handle, int *widthPtr,
        int *heightPtr, TGAHEADER *tgaHeaderPtr);
static int CommonRead(Tcl_Interp *interp, tkimg_MFile *handle,
        const char *filename, Tcl_Obj *format,
        Tk_PhotoHandle imageHandle, int destX, int destY,
        int width, int height, int srcX, int srcY);
static int CommonWrite(Tcl_Interp *interp,
        const char *filename, Tcl_Obj *format,
        tkimg_MFile *handle, Tk_PhotoImageBlock *blockPtr);

static int ParseFormatOpts(interp, format, opts)
    Tcl_Interp *interp;
    Tcl_Obj *format;
    FMTOPT *opts;
{
    static const char *const tgaOptions[] = {
        "-compression", "-verbose", "-matte", NULL
    };
    int objc, i, index;
    char *optionStr;
    Tcl_Obj **objv;
    int boolVal;

    /* Initialize options with default values. */
    opts->compression = TGA_RGB_COMP;
    opts->verbose     = 0;
    opts->matte       = 1;

    if (tkimg_ListObjGetElements(interp, format, &objc, &objv) != TCL_OK) {
        return TCL_ERROR;
    }
    if (objc) {
        for (i=1; i<objc; i++) {
            if (Tcl_GetIndexFromObj(interp, objv[i], (const char *CONST86 *)tgaOptions,
                    "format option", 0, &index) != TCL_OK) {
                return TCL_ERROR;
            }
            if (++i >= objc) {
                Tcl_AppendResult(interp, "No value for option \"",
                        Tcl_GetStringFromObj (objv[--i], (int *) NULL),
                        "\"", (char *) NULL);
                return TCL_ERROR;
            }
            optionStr = Tcl_GetStringFromObj(objv[i], (int *) NULL);
            switch(index) {
                case 0:
                    if (!strncmp (optionStr, "none", strlen ("none"))) {
                        opts->compression = TGA_RGB_UNCOMP;
                    } else if (!strncmp (optionStr, "rle", strlen ("rle"))) {
                        opts->compression = TGA_RGB_COMP;
                    } else {
                        Tcl_AppendResult (interp, "Invalid compression mode \"", optionStr,
                                          "\": Must be \"none\" or \"rle\"", (char *) NULL);
                        return TCL_ERROR;
                    }
                    break;
                case 1:
                    if (Tcl_GetBoolean(interp, optionStr, &boolVal) == TCL_ERROR) {
                        Tcl_AppendResult (interp, "Invalid verbose mode \"", optionStr,
                                          "\": should be 1 or 0, on or off, true or false",
                                          (char *) NULL);
                        return TCL_ERROR;
                    }
                    opts->verbose = boolVal;
                    break;
                case 2:
                    if (Tcl_GetBoolean(interp, optionStr, &boolVal) == TCL_ERROR) {
                        Tcl_AppendResult (interp, "Invalid matte mode \"", optionStr,
                                          "\": should be 1 or 0, on or off, true or false",
                                          (char *) NULL);
                        return TCL_ERROR;
                    }
                    opts->matte = boolVal;
                    break;
            }
        }
    }
    return TCL_OK;
}

static int ChnMatch(
    Tcl_Channel chan,
    const char *filename,
    Tcl_Obj *format,
    int *widthPtr,
    int *heightPtr,
    Tcl_Interp *interp
) {
    tkimg_MFile handle;

    handle.data = (char *) chan;
    handle.state = IMG_CHAN;

    return CommonMatch(&handle, widthPtr, heightPtr, NULL);
}

static int ObjMatch(
    Tcl_Obj *data,
    Tcl_Obj *format,
    int *widthPtr,
    int *heightPtr,
    Tcl_Interp *interp
) {
    tkimg_MFile handle;

    if (!tkimg_ReadInit (data, 0, &handle)) {
        tkimg_ReadInit (data, '*', &handle);
    }
    return CommonMatch(&handle, widthPtr, heightPtr, NULL);
}

static int CommonMatch(
    tkimg_MFile *handle,
    int *widthPtr,
    int *heightPtr,
    TGAHEADER *tgaHeaderPtr
) {
    TGAHEADER th;

    if (!readHeader (handle, &th)) {
        return 0;
    }

    *widthPtr  = th.xsize;
    *heightPtr = th.ysize;
    if (tgaHeaderPtr) {
        *tgaHeaderPtr = th;
    }
    return 1;
}

static int ChnRead(
    Tcl_Interp *interp,         /* Interpreter to use for reporting errors. */
    Tcl_Channel chan,           /* The image channel, open for reading. */
    const char *filename,       /* The name of the image file. */
    Tcl_Obj *format,            /* User-specified format object, or NULL. */
    Tk_PhotoHandle imageHandle, /* The photo image to write into. */
    int destX, int destY,       /* Coordinates of top-left pixel in
                                 * photo image to be written to. */
    int width, int height,      /* Dimensions of block of photo image to
                                 * be written to. */
    int srcX, int srcY          /* Coordinates of top-left pixel to be used
                                 * in image being read. */
) {
    tkimg_MFile handle;

    handle.data = (char *) chan;
    handle.state = IMG_CHAN;

    return CommonRead(interp, &handle, filename, format, imageHandle,
                      destX, destY, width, height, srcX, srcY);
}

static int ObjRead(
    Tcl_Interp *interp,
    Tcl_Obj *data,
    Tcl_Obj *format,
    Tk_PhotoHandle imageHandle,
    int destX, int destY,
    int width, int height,
    int srcX, int srcY
) {
    tkimg_MFile handle;

    if (!tkimg_ReadInit(data, 0, &handle)) {
        tkimg_ReadInit(data, '*', &handle);
    }
    return CommonRead(interp, &handle, "InlineData", format, imageHandle,
                      destX, destY, width, height, srcX, srcY);
}

static int CommonRead(
    Tcl_Interp *interp,         /* Interpreter to use for reporting errors. */
    tkimg_MFile *handle,        /* The image file, open for reading. */
    const char *filename,       /* The name of the image file. */
    Tcl_Obj *format,            /* User-specified format object, or NULL. */
    Tk_PhotoHandle imageHandle, /* The photo image to write into. */
    int destX, int destY,       /* Coordinates of top-left pixel in
                                 * photo image to be written to. */
    int width, int height,      /* Dimensions of block of photo image to
                                 * be written to. */
    int srcX, int srcY          /* Coordinates of top-left pixel to be used
                                 * in image being read. */
) {
    Tk_PhotoImageBlock block;
    Int y, nchan;
    int fileWidth, fileHeight;
    int stopY, outY, outWidth, outHeight;
    TGAFILE tf;
    FMTOPT opts;
    char errMsg[200];
    int result = TCL_OK;

    memset (&tf, 0, sizeof (TGAFILE));
    if (ParseFormatOpts (interp, format, &opts) != TCL_OK) {
        return TCL_ERROR;
    }

    if (!CommonMatch(handle, &fileWidth, &fileHeight, &tf.th)) {
        return TCL_ERROR;
    }
    if (opts.verbose) {
        printImgInfo (&tf.th, filename, "Reading image:");
    }

    if ((srcX + width) > fileWidth) {
        outWidth = fileWidth - srcX;
    } else {
        outWidth = width;
    }
    if ((srcY + height) > fileHeight) {
        outHeight = fileHeight - srcY;
    } else {
        outHeight = height;
    }
    if ((outWidth <= 0) || (outHeight <= 0)
        || (srcX >= fileWidth) || (srcY >= fileHeight)) {
        return TCL_OK;
    }

    if (tkimg_PhotoExpand(interp, imageHandle, destX + outWidth, destY + outHeight) == TCL_ERROR) {
        return TCL_ERROR;
    }

    if (IS_COMPRESSED(tf.th.imgtyp)) {
        tkimg_ReadBuffer(1);
    }

    tf.scanmode = TGA_MODE_DIFF;
    nchan = NCHAN(tf.th.pixsize);

    tf.pixbuf = (UByte *) ckalloc (fileWidth * nchan);
    if (!tf.pixbuf) {
        sprintf(errMsg, "Can't allocate memory of size %d", fileWidth * nchan);
        Tcl_AppendResult(interp, errMsg, (char *)NULL);
        tkimg_ReadBuffer (0);
        return TCL_ERROR;
    }

    block.pixelSize = nchan;
    block.pitch = fileWidth * nchan;
    block.width = outWidth;
    block.height = 1;
    block.offset[0] = 0;
    block.offset[1] = 1;
    block.offset[2] = 2;
    if (nchan < 4) {
        opts.matte = 0;
    }
    block.offset[3] = opts.matte? 3: 0;
    block.pixelPtr = tf.pixbuf + srcX * nchan;

    stopY = srcY + outHeight;

    if (ENC_TOP_BOTTOM (tf.th.imgdes)) {
        outY = destY;
        for (y=0; y<stopY; y++) {
            tgaReadScan(interp, handle, &tf, y);
            if (y >= srcY) {
                if (tkimg_PhotoPutBlock(interp, imageHandle, &block, destX, outY, width, 1,
                    opts.matte? TK_PHOTO_COMPOSITE_OVERLAY: TK_PHOTO_COMPOSITE_SET) == TCL_ERROR) {
                    result = TCL_ERROR;
                    break;
                }
                outY++;
            }
        }
    } else {
        outY = destY + outHeight - 1;
        for (y=fileHeight-1; y>=0; y--) {
            tgaReadScan(interp, handle, &tf, y);
            if (y >= srcY && y < stopY) {
                if (tkimg_PhotoPutBlock(interp, imageHandle, &block, destX, outY, width, 1,
                    TK_PHOTO_COMPOSITE_SET) == TCL_ERROR) {
                    result = TCL_ERROR;
                    break;
                }
                outY--;
            }
        }
    }
    tgaClose(&tf);
    tkimg_ReadBuffer(0);
    return result;
}

static int ChnWrite(
    Tcl_Interp *interp,
    const char *filename,
    Tcl_Obj *format,
    Tk_PhotoImageBlock *blockPtr
) {
    Tcl_Channel chan;
    tkimg_MFile handle;
    int result;

    chan = tkimg_OpenFileChannel(interp, filename, 0644);
    if (!chan) {
        return TCL_ERROR;
    }

    handle.data = (char *) chan;
    handle.state = IMG_CHAN;

    result = CommonWrite(interp, filename, format, &handle, blockPtr);
    if (Tcl_Close(interp, chan) == TCL_ERROR) {
        return TCL_ERROR;
    }
    return result;
}

static int StringWrite(
    Tcl_Interp *interp,
    Tcl_Obj *format,
    Tk_PhotoImageBlock *blockPtr
) {
    tkimg_MFile handle;
    int result;
    Tcl_DString data;

    Tcl_DStringInit(&data);
    tkimg_WriteInit(&data, &handle);
    result = CommonWrite(interp, "InlineData", format, &handle, blockPtr);
    tkimg_Putc(IMG_DONE, &handle);

    if (result == TCL_OK) {
        Tcl_DStringResult(interp, &data);
    } else {
        Tcl_DStringFree(&data);
    }
    return result;
}

static int CommonWrite(
    Tcl_Interp *interp,
    const char *filename,
    Tcl_Obj *format,
    tkimg_MFile *handle,
    Tk_PhotoImageBlock *blockPtr
) {
    Int     x, y, nchan;
    Int     redOffset, greenOffset, blueOffset, alphaOffset;
    UByte   *pixelPtr, *rowPixPtr;
    TGAFILE tf;
    FMTOPT opts;
    char errMsg[200];

    memset(&tf, 0, sizeof(TGAFILE));
    if (ParseFormatOpts(interp, format, &opts) != TCL_OK) {
        return TCL_ERROR;
    }

    redOffset   = 0;
    greenOffset = blockPtr->offset[1] - blockPtr->offset[0];
    blueOffset  = blockPtr->offset[2] - blockPtr->offset[0];
    alphaOffset = blockPtr->offset[0];

    if (alphaOffset < blockPtr->offset[2]) {
        alphaOffset = blockPtr->offset[2];
    }
    if (++alphaOffset < blockPtr->pixelSize) {
        alphaOffset -= blockPtr->offset[0];
    } else {
        alphaOffset = 0;
    }

    nchan = ((opts.matte && alphaOffset)? 4: 3);

    tf.redScan   = (UByte *) ckalloc(blockPtr->width);
    tf.greenScan = (UByte *) ckalloc(blockPtr->width);
    tf.blueScan  = (UByte *) ckalloc(blockPtr->width);
    tf.matteScan = (UByte *) ckalloc(blockPtr->width);
    if (!tf.redScan || !tf.greenScan || !tf.blueScan || !tf.matteScan) {
        sprintf(errMsg, "Can't allocate memory of size %d", blockPtr->width);
        Tcl_AppendResult(interp, errMsg, (char *)NULL);
        return TCL_ERROR;
    }

    /* Fill the targa header struct and write the header to the channel. */
    tf.th.pixsize = nchan * 8;
    tf.th.xsize = blockPtr->width;
    tf.th.ysize = blockPtr->height;
    tf.th.imgdes = (1 << 5);            /* Top->Bottom, Left->Right encoding */
    tf.th.imgtyp = opts.compression;    /* Uncompressed or RLE-compressed */

    if (!writeHeader(handle, &tf.th)) {
        return TCL_ERROR;
    }

    rowPixPtr = blockPtr->pixelPtr + blockPtr->offset[0];
    for (y = 0; y < blockPtr->height; y++) {
        tf.red   = tf.redScan;
        tf.green = tf.greenScan;
        tf.blue  = tf.blueScan;
        tf.matte = tf.matteScan;
        pixelPtr = rowPixPtr;
        for (x = 0; x < blockPtr->width; x++) {
            *(tf.red++)   = pixelPtr[redOffset];
            *(tf.green++) = pixelPtr[greenOffset];
            *(tf.blue++)  = pixelPtr[blueOffset];
            if (nchan == 4) {
                /* Have a matte channel and write it. */
                *(tf.matte++) = pixelPtr[alphaOffset];
            }
            pixelPtr += blockPtr->pixelSize;
        }
        if (!tgaWriteScan(interp, handle, &tf, y)) {
            tgaClose (&tf);
            return TCL_ERROR;
        }
        rowPixPtr += blockPtr->pitch;
    }
    if (opts.verbose) {
        printImgInfo(&tf.th, filename, "Saving image:");
    }
    tgaClose (&tf);
    return TCL_OK;
}
