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tkImgGIF.c
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tkImgGIF.c
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/*
* tkImgGIF.c --
*
* A photo image file handler for GIF files. Reads 87a and 89a GIF files.
* At present, there only is a file write function. GIF images may be
* read using the -data option of the photo image. The data may be given
* as a binary string in a Tcl_Obj or by representing the data as BASE64
* encoded ascii. Derived from the giftoppm code found in the pbmplus
* package and tkImgFmtPPM.c in the tk4.0b2 distribution.
*
* Copyright (c) Reed Wade (wade@cs.utk.edu), University of Tennessee
* Copyright (c) 1995-1997 Sun Microsystems, Inc.
* Copyright (c) 1997 Australian National University
* Copyright (c) 2005 Donal K. Fellows
*
* See the file "license.terms" for information on usage and redistribution of
* this file, and for a DISCLAIMER OF ALL WARRANTIES.
*
* This file also contains code from the giftoppm program, which is
* copyrighted as follows:
*
* +--------------------------------------------------------------------+
* | Copyright 1990, David Koblas. |
* | Permission to use, copy, modify, and distribute this software |
* | and its documentation for any purpose and without fee is hereby |
* | granted, provided that the above copyright notice appear in all |
* | copies and that both that copyright notice and this permission |
* | notice appear in supporting documentation. This software is |
* | provided "as is" without express or implied warranty. |
* +--------------------------------------------------------------------+
*
* This file also contains code from miGIF. See lower down in file for the
* applicable copyright notice for that portion.
*/
#include "tkInt.h"
/*
* GIF's are represented as data in either binary or base64 format. base64
* strings consist of 4 6-bit characters -> 3 8 bit bytes. A-Z, a-z, 0-9, +
* and / represent the 64 values (in order). '=' is a trailing padding char
* when the un-encoded data is not a multiple of 3 bytes. We'll ignore white
* space when encountered. Any other invalid character is treated as an EOF
*/
#define GIF_SPECIAL (256)
#define GIF_PAD (GIF_SPECIAL+1)
#define GIF_SPACE (GIF_SPECIAL+2)
#define GIF_BAD (GIF_SPECIAL+3)
#define GIF_DONE (GIF_SPECIAL+4)
/*
* structure to "mimic" FILE for Mread, so we can look like fread. The decoder
* state keeps track of which byte we are about to read, or EOF.
*/
typedef struct mFile {
unsigned char *data; /* mmencoded source string */
int c; /* bits left over from previous character */
int state; /* decoder state (0-4 or GIF_DONE) */
int length; /* Total amount of bytes in data */
} MFile;
/*
* Non-ASCII encoding support:
* Most data in a GIF image is binary and is treated as such. However, a few
* key bits are stashed in ASCII. If we try to compare those pieces to the
* char they represent, it will fail on any non-ASCII (eg, EBCDIC) system. To
* accomodate these systems, we test against the numeric value of the ASCII
* characters instead of the characters themselves. This is encoding
* independant.
*/
static const char GIF87a[] = { /* ASCII GIF87a */
0x47, 0x49, 0x46, 0x38, 0x37, 0x61, 0x00
};
static const char GIF89a[] = { /* ASCII GIF89a */
0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x00
};
#define GIF_TERMINATOR 0x3b /* ASCII ; */
#define GIF_EXTENSION 0x21 /* ASCII ! */
#define GIF_START 0x2c /* ASCII , */
/*
* Flags used to notify that we've got inline data instead of a file to read
* from. Note that we need to figure out which type of inline data we've got
* before handing off to the GIF reading code; this is done in StringReadGIF.
*/
#define INLINE_DATA_BINARY ((const char *) 0x01)
#define INLINE_DATA_BASE64 ((const char *) 0x02)
/*
* HACK ALERT!! HACK ALERT!! HACK ALERT!!
* This code is hard-wired for reading from files. In order to read from a
* data stream, we'll trick fread so we can reuse the same code. 0==from file;
* 1==from base64 encoded data; 2==from binary data
*/
typedef struct {
const char *fromData;
unsigned char workingBuffer[280];
struct {
int bytes;
int done;
unsigned int window;
int bitsInWindow;
unsigned char *c;
} reader;
} GIFImageConfig;
/*
* The format record for the GIF file format:
*/
static int FileMatchGIF(Tcl_Channel chan, const char *fileName,
Tcl_Obj *format, int *widthPtr, int *heightPtr,
Tcl_Interp *interp);
static int FileReadGIF(Tcl_Interp *interp, Tcl_Channel chan,
const char *fileName, Tcl_Obj *format,
Tk_PhotoHandle imageHandle, int destX, int destY,
int width, int height, int srcX, int srcY);
static int StringMatchGIF(Tcl_Obj *dataObj, Tcl_Obj *format,
int *widthPtr, int *heightPtr, Tcl_Interp *interp);
static int StringReadGIF(Tcl_Interp *interp, Tcl_Obj *dataObj,
Tcl_Obj *format, Tk_PhotoHandle imageHandle,
int destX, int destY, int width, int height,
int srcX, int srcY);
static int FileWriteGIF(Tcl_Interp *interp, const char *filename,
Tcl_Obj *format, Tk_PhotoImageBlock *blockPtr);
static int CommonWriteGIF(Tcl_Interp *interp, Tcl_Channel handle,
Tcl_Obj *format, Tk_PhotoImageBlock *blockPtr);
Tk_PhotoImageFormat tkImgFmtGIF = {
"gif", /* name */
FileMatchGIF, /* fileMatchProc */
StringMatchGIF, /* stringMatchProc */
FileReadGIF, /* fileReadProc */
StringReadGIF, /* stringReadProc */
FileWriteGIF, /* fileWriteProc */
NULL, /* stringWriteProc */
};
#define INTERLACE 0x40
#define LOCALCOLORMAP 0x80
#define BitSet(byte, bit) (((byte) & (bit)) == (bit))
#define MAXCOLORMAPSIZE 256
#define CM_RED 0
#define CM_GREEN 1
#define CM_BLUE 2
#define CM_ALPHA 3
#define MAX_LWZ_BITS 12
#define LM_to_uint(a,b) (((b)<<8)|(a))
/*
* Prototypes for local functions defined in this file:
*/
static int DoExtension(GIFImageConfig *gifConfPtr,
Tcl_Channel chan, int label, unsigned char *buffer,
int *transparent);
static int GetCode(Tcl_Channel chan, int code_size, int flag,
GIFImageConfig *gifConfPtr);
static int GetDataBlock(GIFImageConfig *gifConfPtr,
Tcl_Channel chan, unsigned char *buf);
static int ReadColorMap(GIFImageConfig *gifConfPtr,
Tcl_Channel chan, int number,
unsigned char buffer[MAXCOLORMAPSIZE][4]);
static int ReadGIFHeader(GIFImageConfig *gifConfPtr,
Tcl_Channel chan, int *widthPtr, int *heightPtr);
static int ReadImage(GIFImageConfig *gifConfPtr,
Tcl_Interp *interp, unsigned char *imagePtr,
Tcl_Channel chan, int len, int rows,
unsigned char cmap[MAXCOLORMAPSIZE][4], int srcX,
int srcY, int interlace, int transparent);
/*
* these are for the BASE64 image reader code only
*/
static int Fread(GIFImageConfig *gifConfPtr, unsigned char *dst,
size_t size, size_t count, Tcl_Channel chan);
static int Mread(unsigned char *dst, size_t size, size_t count,
MFile *handle);
static int Mgetc(MFile *handle);
static int char64(int c);
static void mInit(unsigned char *string, MFile *handle,
int length);
/*
*----------------------------------------------------------------------
*
* FileMatchGIF --
*
* This function is invoked by the photo image type to see if a file
* contains image data in GIF format.
*
* Results:
* The return value is 1 if the first characters in file f look like GIF
* data, and 0 otherwise.
*
* Side effects:
* The access position in f may change.
*
*----------------------------------------------------------------------
*/
static int
FileMatchGIF(
Tcl_Channel chan, /* The image file, open for reading. */
const char *fileName, /* The name of the image file. */
Tcl_Obj *format, /* User-specified format object, or NULL. */
int *widthPtr, int *heightPtr,
/* The dimensions of the image are returned
* here if the file is a valid raw GIF file. */
Tcl_Interp *interp) /* not used */
{
GIFImageConfig gifConf;
memset(&gifConf, 0, sizeof(GIFImageConfig));
return ReadGIFHeader(&gifConf, chan, widthPtr, heightPtr);
}
/*
*----------------------------------------------------------------------
*
* FileReadGIF --
*
* This function is called by the photo image type to read GIF format
* data from a file and write it into a given photo image.
*
* Results:
* A standard TCL completion code. If TCL_ERROR is returned then an error
* message is left in the interp's result.
*
* Side effects:
* The access position in file f is changed, and new data is added to the
* image given by imageHandle.
*
*----------------------------------------------------------------------
*/
static int
FileReadGIF(
Tcl_Interp *interp, /* Interpreter to use for reporting errors. */
Tcl_Channel chan, /* 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. */
{
int fileWidth, fileHeight, imageWidth, imageHeight;
int nBytes, index = 0, argc = 0, i, result = TCL_ERROR;
Tcl_Obj **objv;
unsigned char buf[100];
unsigned char *trashBuffer = NULL;
int bitPixel;
unsigned char colorMap[MAXCOLORMAPSIZE][4];
int transparent = -1;
static const char *optionStrings[] = {
"-index", NULL
};
GIFImageConfig gifConf, *gifConfPtr = &gifConf;
/*
* Decode the magic used to convey when we're sourcing data from a string
* source and not a file.
*/
memset(gifConfPtr, 0, sizeof(GIFImageConfig));
if (fileName == INLINE_DATA_BINARY || fileName == INLINE_DATA_BASE64) {
gifConfPtr->fromData = fileName;
fileName = "inline data";
}
/*
* Parse the format string to get options.
*/
if (format && Tcl_ListObjGetElements(interp, format,
&argc, &objv) != TCL_OK) {
return TCL_ERROR;
}
for (i = 1; i < argc; i++) {
if (Tcl_GetIndexFromObj(interp, objv[i], optionStrings, "option name",
0, &nBytes) != TCL_OK) {
return TCL_ERROR;
}
if (i == (argc-1)) {
Tcl_AppendResult(interp, "no value given for \"",
Tcl_GetString(objv[i]), "\" option", NULL);
return TCL_ERROR;
}
if (Tcl_GetIntFromObj(interp, objv[++i], &index) != TCL_OK) {
return TCL_ERROR;
}
}
/*
* Read the GIF file header and check for some sanity.
*/
if (!ReadGIFHeader(gifConfPtr, chan, &fileWidth, &fileHeight)) {
Tcl_AppendResult(interp, "couldn't read GIF header from file \"",
fileName, "\"", NULL);
return TCL_ERROR;
}
if ((fileWidth <= 0) || (fileHeight <= 0)) {
Tcl_AppendResult(interp, "GIF image file \"", fileName,
"\" has dimension(s) <= 0", NULL);
return TCL_ERROR;
}
/*
* Get the general colormap information.
*/
if (Fread(gifConfPtr, buf, 1, 3, chan) != 3) {
return TCL_OK;
}
bitPixel = 2 << (buf[0] & 0x07);
if (BitSet(buf[0], LOCALCOLORMAP)) { /* Global Colormap */
if (!ReadColorMap(gifConfPtr, chan, bitPixel, colorMap)) {
Tcl_AppendResult(interp, "error reading color map", NULL);
return TCL_ERROR;
}
}
if ((srcX + width) > fileWidth) {
width = fileWidth - srcX;
}
if ((srcY + height) > fileHeight) {
height = fileHeight - srcY;
}
if ((width <= 0) || (height <= 0)
|| (srcX >= fileWidth) || (srcY >= fileHeight)) {
return TCL_OK;
}
/*
* Make sure we have enough space in the photo image to hold the data from
* the GIF.
*/
if (Tk_PhotoExpand(interp, imageHandle,
destX + width, destY + height) != TCL_OK) {
return TCL_ERROR;
}
/*
* Search for the frame from the GIF to display.
*/
while (1) {
if (Fread(gifConfPtr, buf, 1, 1, chan) != 1) {
/*
* Premature end of image.
*/
Tcl_AppendResult(interp,
"premature end of image data for this index", NULL);
goto error;
}
switch (buf[0]) {
case GIF_TERMINATOR:
Tcl_AppendResult(interp, "no image data for this index", NULL);
goto error;
case GIF_EXTENSION:
/*
* This is a GIF extension.
*/
if (Fread(gifConfPtr, buf, 1, 1, chan) != 1) {
Tcl_SetResult(interp,
"error reading extension function code in GIF image",
TCL_STATIC);
goto error;
}
if (DoExtension(gifConfPtr, chan, buf[0],
gifConfPtr->workingBuffer, &transparent) < 0) {
Tcl_SetResult(interp, "error reading extension in GIF image",
TCL_STATIC);
goto error;
}
continue;
case GIF_START:
if (Fread(gifConfPtr, buf, 1, 9, chan) != 9) {
Tcl_SetResult(interp,
"couldn't read left/top/width/height in GIF image",
TCL_STATIC);
goto error;
}
break;
default:
/*
* Not a valid start character; ignore it.
*/
continue;
}
/*
* We've read the header for a GIF frame. Work out what we are going
* to do about it.
*/
imageWidth = LM_to_uint(buf[4], buf[5]);
imageHeight = LM_to_uint(buf[6], buf[7]);
bitPixel = 1 << ((buf[8] & 0x07) + 1);
if (index--) {
/*
* This is not the GIF frame we want to read: skip it.
*/
if (BitSet(buf[8], LOCALCOLORMAP)) {
if (!ReadColorMap(gifConfPtr, chan, bitPixel, colorMap)) {
Tcl_AppendResult(interp, "error reading color map", NULL);
goto error;
}
}
/*
* If we've not yet allocated a trash buffer, do so now.
*/
if (trashBuffer == NULL) {
nBytes = fileWidth * fileHeight * 3;
trashBuffer = (unsigned char *) ckalloc((unsigned) nBytes);
}
/*
* Slurp! Process the data for this image and stuff it in a trash
* buffer.
*
* Yes, it might be more efficient here to *not* store the data
* (we're just going to throw it away later). However, I elected
* to implement it this way for good reasons. First, I wanted to
* avoid duplicating the (fairly complex) LWZ decoder in
* ReadImage. Fine, you say, why didn't you just modify it to
* allow the use of a NULL specifier for the output buffer? I
* tried that, but it negatively impacted the performance of what
* I think will be the common case: reading the first image in the
* file. Rather than marginally improve the speed of the less
* frequent case, I chose to maintain high performance for the
* common case.
*/
if (ReadImage(gifConfPtr, interp, trashBuffer, chan, imageWidth,
imageHeight, colorMap, 0, 0, 0, -1) != TCL_OK) {
goto error;
}
continue;
}
break;
}
/*
* Found the frame we want to read. Next, check for a local color map for
* this frame.
*/
if (BitSet(buf[8], LOCALCOLORMAP)) {
if (!ReadColorMap(gifConfPtr, chan, bitPixel, colorMap)) {
Tcl_AppendResult(interp, "error reading color map", NULL);
goto error;
}
}
/*
* Extract the location within the overall visible image to put the data
* in this frame, together with the size of this frame.
*/
index = LM_to_uint(buf[0], buf[1]);
srcX -= index;
if (srcX<0) {
destX -= srcX; width += srcX;
srcX = 0;
}
if (width > imageWidth) {
width = imageWidth;
}
index = LM_to_uint(buf[2], buf[3]);
srcY -= index;
if (index > srcY) {
destY -= srcY; height += srcY;
srcY = 0;
}
if (height > imageHeight) {
height = imageHeight;
}
if ((width > 0) && (height > 0)) {
Tk_PhotoImageBlock block;
/*
* Read the data and put it into the photo buffer for display by the
* general image machinery.
*/
block.width = width;
block.height = height;
block.pixelSize = (transparent>=0) ? 4 : 3;
block.offset[0] = 0;
block.offset[1] = 1;
block.offset[2] = 2;
block.offset[3] = (transparent>=0) ? 3 : 0;
block.pitch = block.pixelSize * imageWidth;
nBytes = block.pitch * imageHeight;
block.pixelPtr = (unsigned char *) ckalloc((unsigned) nBytes);
if (ReadImage(gifConfPtr, interp, block.pixelPtr, chan, imageWidth,
imageHeight, colorMap, srcX, srcY, BitSet(buf[8],INTERLACE),
transparent) != TCL_OK) {
ckfree((char *) block.pixelPtr);
goto error;
}
if (Tk_PhotoPutBlock(interp, imageHandle, &block, destX, destY,
width, height, TK_PHOTO_COMPOSITE_SET) != TCL_OK) {
ckfree((char *) block.pixelPtr);
goto error;
}
ckfree((char *) block.pixelPtr);
}
/*
* We've successfully read the GIF frame (or there was nothing to read,
* which suits as well). We're done.
*/
Tcl_AppendResult(interp, tkImgFmtGIF.name, NULL);
result = TCL_OK;
error:
/*
* If a trash buffer has been allocated, free it now.
*/
if (trashBuffer != NULL) {
ckfree((char *) trashBuffer);
}
return result;
}
/*
*----------------------------------------------------------------------
*
* StringMatchGIF --
*
* This function is invoked by the photo image type to see if an object
* contains image data in GIF format.
*
* Results:
* The return value is 1 if the first characters in the data are like GIF
* data, and 0 otherwise.
*
* Side effects:
* The size of the image is placed in widthPtr and heightPtr.
*
*----------------------------------------------------------------------
*/
static int
StringMatchGIF(
Tcl_Obj *dataObj, /* the object containing the image data */
Tcl_Obj *format, /* the image format object, or NULL */
int *widthPtr, /* where to put the string width */
int *heightPtr, /* where to put the string height */
Tcl_Interp *interp) /* not used */
{
unsigned char *data, header[10];
int got, length;
MFile handle;
data = Tcl_GetByteArrayFromObj(dataObj, &length);
/*
* Header is a minimum of 10 bytes.
*/
if (length < 10) {
return 0;
}
/*
* Check whether the data is Base64 encoded.
*/
if ((strncmp(GIF87a, (char *) data, 6) != 0) &&
(strncmp(GIF89a, (char *) data, 6) != 0)) {
/*
* Try interpreting the data as Base64 encoded
*/
mInit((unsigned char *) data, &handle, length);
got = Mread(header, 10, 1, &handle);
if (got != 10 ||
((strncmp(GIF87a, (char *) header, 6) != 0)
&& (strncmp(GIF89a, (char *) header, 6) != 0))) {
return 0;
}
} else {
memcpy(header, data, 10);
}
*widthPtr = LM_to_uint(header[6], header[7]);
*heightPtr = LM_to_uint(header[8], header[9]);
return 1;
}
/*
*----------------------------------------------------------------------
*
* StringReadGIF --
*
* This function is called by the photo image type to read GIF format
* data from an object, optionally base64 encoded, and give it to the
* photo image.
*
* Results:
* A standard TCL completion code. If TCL_ERROR is returned then an error
* message is left in the interp's result.
*
* Side effects:
* New data is added to the image given by imageHandle. This function
* calls FileReadGIF by redefining the operation of fprintf temporarily.
*
*----------------------------------------------------------------------
*/
static int
StringReadGIF(
Tcl_Interp *interp, /* interpreter for reporting errors in */
Tcl_Obj *dataObj, /* object containing the image */
Tcl_Obj *format, /* format object, or NULL */
Tk_PhotoHandle imageHandle, /* the image to write this data into */
int destX, int destY, /* The rectangular region of the */
int width, int height, /* image to copy */
int srcX, int srcY)
{
MFile handle, *hdlPtr = &handle;
int length;
const char *xferFormat;
unsigned char *data = Tcl_GetByteArrayFromObj(dataObj, &length);
mInit(data, hdlPtr, length);
/*
* Check whether the data is Base64 encoded by doing a character-by-
* charcter comparison with the binary-format headers; BASE64-encoded
* never matches (matching the other way is harder because of potential
* padding of the BASE64 data).
*/
if (strncmp(GIF87a, (char *) data, 6)
&& strncmp(GIF89a, (char *) data, 6)) {
xferFormat = INLINE_DATA_BASE64;
} else {
xferFormat = INLINE_DATA_BINARY;
}
/*
* Fall through to the file reader now that we have a correctly-configured
* pseudo-channel to pull the data from.
*/
return FileReadGIF(interp, (Tcl_Channel) hdlPtr, xferFormat, format,
imageHandle, destX, destY, width, height, srcX, srcY);
}
/*
*----------------------------------------------------------------------
*
* ReadGIFHeader --
*
* This function reads the GIF header from the beginning of a GIF file
* and returns the dimensions of the image.
*
* Results:
* The return value is 1 if file "f" appears to start with a valid GIF
* header, 0 otherwise. If the header is valid, then *widthPtr and
* *heightPtr are modified to hold the dimensions of the image.
*
* Side effects:
* The access position in f advances.
*
*----------------------------------------------------------------------
*/
static int
ReadGIFHeader(
GIFImageConfig *gifConfPtr,
Tcl_Channel chan, /* Image file to read the header from */
int *widthPtr, int *heightPtr)
/* The dimensions of the image are returned
* here. */
{
unsigned char buf[7];
if ((Fread(gifConfPtr, buf, 1, 6, chan) != 6)
|| ((strncmp(GIF87a, (char *) buf, 6) != 0)
&& (strncmp(GIF89a, (char *) buf, 6) != 0))) {
return 0;
}
if (Fread(gifConfPtr, buf, 1, 4, chan) != 4) {
return 0;
}
*widthPtr = LM_to_uint(buf[0], buf[1]);
*heightPtr = LM_to_uint(buf[2], buf[3]);
return 1;
}
/*
*-----------------------------------------------------------------
* The code below is copied from the giftoppm program and modified just
* slightly.
*-----------------------------------------------------------------
*/
static int
ReadColorMap(
GIFImageConfig *gifConfPtr,
Tcl_Channel chan,
int number,
unsigned char buffer[MAXCOLORMAPSIZE][4])
{
int i;
unsigned char rgb[3];
for (i = 0; i < number; ++i) {
if (Fread(gifConfPtr, rgb, sizeof(rgb), 1, chan) <= 0) {
return 0;
}
if (buffer) {
buffer[i][CM_RED] = rgb[0];
buffer[i][CM_GREEN] = rgb[1];
buffer[i][CM_BLUE] = rgb[2];
buffer[i][CM_ALPHA] = 255;
}
}
return 1;
}
static int
DoExtension(
GIFImageConfig *gifConfPtr,
Tcl_Channel chan,
int label,
unsigned char *buf,
int *transparent)
{
int count;
switch (label) {
case 0x01: /* Plain Text Extension */
break;
case 0xff: /* Application Extension */
break;
case 0xfe: /* Comment Extension */
do {
count = GetDataBlock(gifConfPtr, chan, buf);
} while (count > 0);
return count;
case 0xf9: /* Graphic Control Extension */
count = GetDataBlock(gifConfPtr, chan, buf);
if (count < 0) {
return 1;
}
if ((buf[0] & 0x1) != 0) {
*transparent = buf[3];
}
do {
count = GetDataBlock(gifConfPtr, chan, buf);
} while (count > 0);
return count;
}
do {
count = GetDataBlock(gifConfPtr, chan, buf);
} while (count > 0);
return count;
}
static int
GetDataBlock(
GIFImageConfig *gifConfPtr,
Tcl_Channel chan,
unsigned char *buf)
{
unsigned char count;
if (Fread(gifConfPtr, &count, 1, 1, chan) <= 0) {
return -1;
}
if ((count != 0) && (Fread(gifConfPtr, buf, count, 1, chan) <= 0)) {
return -1;
}
return count;
}
/*
*----------------------------------------------------------------------
*
* ReadImage --
*
* Process a GIF image from a given source, with a given height, width,
* transparency, etc.
*
* This code is based on the code found in the ImageMagick GIF decoder,
* which is (c) 2000 ImageMagick Studio.
*
* Some thoughts on our implementation:
* It sure would be nice if ReadImage didn't take 11 parameters! I think
* that if we were smarter, we could avoid doing that.
*
* Possible further optimizations: we could pull the GetCode function
* directly into ReadImage, which would improve our speed.
*
* Results:
* Processes a GIF image and loads the pixel data into a memory array.
*
* Side effects:
* None.
*
*----------------------------------------------------------------------
*/
static int
ReadImage(
GIFImageConfig *gifConfPtr,
Tcl_Interp *interp,
unsigned char *imagePtr,
Tcl_Channel chan,
int len, int rows,
unsigned char cmap[MAXCOLORMAPSIZE][4],
int srcX, int srcY,
int interlace,
int transparent)
{
unsigned char initialCodeSize;
int xpos = 0, ypos = 0, pass = 0, i;
register unsigned char *pixelPtr;
static const int interlaceStep[] = { 8, 8, 4, 2 };
static const int interlaceStart[] = { 0, 4, 2, 1 };
unsigned short prefix[(1 << MAX_LWZ_BITS)];
unsigned char append[(1 << MAX_LWZ_BITS)];
unsigned char stack[(1 << MAX_LWZ_BITS)*2];
register unsigned char *top;
int codeSize, clearCode, inCode, endCode, oldCode, maxCode;
int code, firstCode, v;
/*
* Initialize the decoder
*/
if (Fread(gifConfPtr, &initialCodeSize, 1, 1, chan) <= 0) {
Tcl_AppendResult(interp, "error reading GIF image: ",
Tcl_PosixError(interp), NULL);
return TCL_ERROR;
}
if (initialCodeSize > MAX_LWZ_BITS) {
Tcl_SetResult(interp, "malformed image", TCL_STATIC);
return TCL_ERROR;
}
if (transparent != -1) {
cmap[transparent][CM_RED] = 0;
cmap[transparent][CM_GREEN] = 0;
cmap[transparent][CM_BLUE] = 0;
cmap[transparent][CM_ALPHA] = 0;
}
pixelPtr = imagePtr;
/*
* Initialize the decoder.
*
* Set values for "special" numbers:
* clear code reset the decoder
* end code stop decoding
* code size size of the next code to retrieve
* max code next available table position
*/
clearCode = 1 << (int) initialCodeSize;
endCode = clearCode + 1;
codeSize = (int) initialCodeSize + 1;
maxCode = clearCode + 2;
oldCode = -1;
firstCode = -1;
memset(prefix, 0, (1 << MAX_LWZ_BITS) * sizeof(short));
memset(append, 0, (1 << MAX_LWZ_BITS) * sizeof(char));
for (i = 0; i < clearCode; i++) {
append[i] = i;
}
top = stack;
GetCode(chan, 0, 1, gifConfPtr);
/*
* Read until we finish the image
*/
for (i = 0, ypos = 0; i < rows; i++) {
for (xpos = 0; xpos < len; ) {
if (top == stack) {
/*
* Bummer - our stack is empty. Now we have to work!
*/
code = GetCode(chan, codeSize, 0, gifConfPtr);
if (code < 0) {
return TCL_OK;
}
if (code > maxCode || code == endCode) {
/*
* If we're doing things right, we should never receive a
* code that is greater than our current maximum code. If
* we do, bail, because our decoder does not yet have that
* code set up.
*
* If the code is the magic endCode value, quit.
*/
return TCL_OK;
}
if (code == clearCode) {
/*
* Reset the decoder.
*/
codeSize = initialCodeSize + 1;
maxCode = clearCode + 2;
oldCode = -1;
continue;
}
if (oldCode == -1) {
/*
* Last pass reset the decoder, so the first code we see
* must be a singleton. Seed the stack with it, and set up
* the old/first code pointers for insertion into the
* string table. We can't just roll this into the
* clearCode test above, because at that point we have not
* yet read the next code.
*/
*top++ = append[code];
oldCode = code;
firstCode = code;
continue;
}
inCode = code;
if (code == maxCode) {
/*
* maxCode is always one bigger than our highest assigned
* code. If the code we see is equal to maxCode, then we
* are about to add a new string to the table. ???
*/
*top++ = firstCode;
code = oldCode;
}
while (code > clearCode) {
/*
* Populate the stack by tracing the string in the string
* table from its tail to its head
*/
*top++ = append[code];
code = prefix[code];
}
firstCode = append[code];