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gif.c
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C/C++ Source or Header
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1991-07-24
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11KB
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#ident "@(#)gif.c 1.5 91/04/01 XGRASP"
/*-
* gif.c - routine to load GIF images (hacked from gif2ras).
*
* Copyright (c) 1991 by Patrick J. Naughton
*
* 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 file is provided AS IS with no warranties of any kind. The author
* shall have no liability with respect to the infringement of copyrights,
* trade secrets or any patents by this file or any part thereof. In no
* event will the author be liable for any lost revenue or profits or
* other special, indirect and consequential damages.
*
* Comments and additions should be sent to the author:
*
* Patrick J. Naughton
* Sun Microsystems
* 2550 Garcia Ave, MS 10-20
* Mountain View, CA 94043
* (415) 336-1080
*
*/
#include "grasp.h"
#define NEXTBYTE (*ptr++)
#define IMAGESEP 0x2c
#define INTERLACEMASK 0x40
#define COLORMAPMASK 0x80
static int BitOffset, /* Bit Offset of next code */
XC, YC, /* Output X and Y coords of current pixel */
Pass, /* Used by output routine if interlaced pic */
OutCount, /* Decompressor output 'stack count' */
RWidth, RHeight, /* screen dimensions */
Width, Height, /* image dimensions */
LeftOfs, TopOfs, /* image offset */
BitsPerPixel, /* Bits per pixel, read from GIF header */
ColorMapSize, /* number of colors */
CodeSize, /* Code size, read from GIF header */
InitCodeSize, /* Starting code size, used during Clear */
LZWCode, /* Value returned by ReadCode */
MaxCode, /* limiting value for current code size */
ClearCode, /* GIF clear code */
EOFCode, /* GIF end-of-information code */
CurCode, OldCode, InCode, /* Decompressor variables */
FirstFree, /* First free code, generated per GIF spec */
FreeCode, /* Decompressor, next free slot in hash table */
FinChar, /* Decompressor variable */
BitMask, /* AND mask for data size */
ReadMask, /* Code AND mask for current code size */
Interlace, HasColormap;
static u_char *Image; /* The result array */
static u_char *RawGIF; /* The heap array to hold it, raw */
static u_char *Raster; /* The raster data stream, unblocked */
/* The hash table used by the decompressor */
static int Prefix[4096];
static int Suffix[4096];
/* An output array used by the decompressor */
static int OutCode[1025];
static char *id = "GIF87a";
/* Fetch the next code from the raster data stream. The codes can be
* any length from 3 to 12 bits, packed into 8-bit bytes, so we have to
* maintain our location in the Raster array as a BIT Offset. We compute
* the byte Offset into the raster array by dividing this by 8, pick up
* three bytes, compute the bit Offset into our 24-bit chunk, shift to
* bring the desired code to the bottom, then mask it off and return it.
*/
static int
ReadCode()
{
int RawCode, ByteOffset;
ByteOffset = BitOffset / 8;
RawCode = Raster[ByteOffset] + (0x100 * Raster[ByteOffset + 1]);
if (CodeSize >= 8)
RawCode += (0x10000 * Raster[ByteOffset + 2]);
RawCode >>= (BitOffset % 8);
BitOffset += CodeSize;
return (RawCode & ReadMask);
}
static void
AddToPixel(Index)
u_char Index;
{
*(Image + YC * Width + XC) = Index;
/* Update the X-coordinate, and if it overflows, update the Y-coordinate */
if (++XC == Width) {
/* If a non-interlaced picture, just increment YC to the next scan line.
* If it's interlaced, deal with the interlace as described in the GIF
* spec. Put the decoded scan line out to the screen if we haven't gone
* past the bottom of it
*/
XC = 0;
if (!Interlace)
YC++;
else {
switch (Pass) {
case 0:
YC += 8;
if (YC >= Height) {
Pass++;
YC = 4;
}
break;
case 1:
YC += 8;
if (YC >= Height) {
Pass++;
YC = 2;
}
break;
case 2:
YC += 4;
if (YC >= Height) {
Pass++;
YC = 1;
}
break;
case 3:
YC += 2;
break;
default:
break;
}
}
}
}
ImageStruct *
readgifimage(fp, dirent)
FILE *fp;
FilenameStruct *dirent;
{
ImageStruct *im;
XImage *xim;
int filesize;
u_char ch, ch1;
u_char *ptr, *ptr1;
int i;
BitOffset = 0;
XC = 0;
YC = 0;
Pass = 0;
OutCount = 0;
im = (ImageStruct *) malloc(sizeof(ImageStruct));
fseek(fp, dirent->offset, 0);
filesize = GetLong(fp); /* length of whole image file... */
im->name = strtok(strdup(dirent->fname), ".");
im->type = EXT_GIF;
im->xoff = 0;
im->yoff = 0;
if (!(ptr = RawGIF = (u_char *) malloc(filesize)))
error("%s: not enough memory to read gif file.\n", NULL);
if (!(Raster = (u_char *) malloc(filesize)))
error("%s: not enough memory to read gif file.\n", NULL);
if (fread(ptr, filesize, 1, fp) != 1)
error("%s: GIF data read failed\n", NULL);
if (strncmp(ptr, id, 6)) {
free(im->name);
free(im);
free(Raster);
free(ptr);
return (ImageStruct *) readimage(fp, dirent, EXT_PIC);
}
ptr += 6;
/* Get variables from the GIF screen descriptor */
ch = NEXTBYTE;
RWidth = ch + 0x100 * NEXTBYTE; /* screen dimensions... not used. */
ch = NEXTBYTE;
RHeight = ch + 0x100 * NEXTBYTE;
ch = NEXTBYTE;
HasColormap = ((ch & COLORMAPMASK) ? True : False);
BitsPerPixel = (ch & 7) + 1;
im->cmaplen = 1 << BitsPerPixel;
BitMask = im->cmaplen - 1;
ch = NEXTBYTE; /* background color... not used. */
if (NEXTBYTE) /* supposed to be NULL */
error("%s: %s is a corrupt GIF file (nonull).\n", im->name);
/* Read in global colormap. */
if (HasColormap) {
unsigned long pmasks;
u_long pixels[256];
im->cmap = XCreateColormap(dsp, win, vis, AllocNone);
XAllocColorCells(dsp, im->cmap, True, &pmasks, 0, pixels, im->cmaplen);
for (i = 0; i < im->cmaplen; i++) {
im->colors[i].pixel = pixels[i];
im->colors[i].red = NEXTBYTE << 8;
im->colors[i].green = NEXTBYTE << 8;
im->colors[i].blue = NEXTBYTE << 8;
im->colors[i].flags = DoRed | DoGreen | DoBlue;
if (imverbose) {
printf("%02x%02x%02x ",
im->colors[i].red >> 8,
im->colors[i].green >> 8,
im->colors[i].blue >> 8);
if (!((i + 1) % 8))
printf("\n");
}
}
XStoreColors(dsp, im->cmap, im->colors, im->cmaplen);
} else
im->cmap = (Colormap) 0;
/* Check for image seperator */
if (NEXTBYTE != IMAGESEP)
error("%s: %s is a corrupt GIF file (nosep).\n", im->name);
/* Now read in values from the image descriptor */
ch = NEXTBYTE;
LeftOfs = ch + 0x100 * NEXTBYTE;
ch = NEXTBYTE;
TopOfs = ch + 0x100 * NEXTBYTE;
ch = NEXTBYTE;
Width = ch + 0x100 * NEXTBYTE;
ch = NEXTBYTE;
Height = ch + 0x100 * NEXTBYTE;
Interlace = ((NEXTBYTE & INTERLACEMASK) ? True : False);
if (verbose)
fprintf(stderr, "%s: (GIF) %dx%dx%d %s\n",
im->name, Width, Height, 8,
(Interlace) ? "Interlaced" : "");
/* Note that I ignore the possible existence of a local color map.
* I'm told there aren't many files around that use them, and the spec
* says it's defined for future use. This could lead to an error
* reading some files.
*/
/* Start reading the raster data. First we get the intial code size
* and compute decompressor constant values, based on this code size.
*/
CodeSize = NEXTBYTE;
ClearCode = (1 << CodeSize);
EOFCode = ClearCode + 1;
FreeCode = FirstFree = ClearCode + 2;
/* The GIF spec has it that the code size is the code size used to
* compute the above values is the code size given in the file, but the
* code size used in compression/decompression is the code size given in
* the file plus one. (thus the ++).
*/
CodeSize++;
InitCodeSize = CodeSize;
MaxCode = (1 << CodeSize);
ReadMask = MaxCode - 1;
/* Read the raster data. Here we just transpose it from the GIF array
* to the Raster array, turning it from a series of blocks into one long
* data stream, which makes life much easier for ReadCode().
*/
ptr1 = Raster;
do {
ch = ch1 = NEXTBYTE;
while (ch--)
*ptr1++ = NEXTBYTE;
if ((Raster - ptr1) > filesize)
error("%s: %s is a corrupt GIF file (unblock).\n", im->name);
} while (ch1);
free(RawGIF); /* We're done with the raw data now... */
Image = (u_char *) malloc(Width * Height);
if (!Image)
error("%s: malloc failed on image data.\n");
/* Decompress the file, continuing until you see the GIF EOF code.
* One obvious enhancement is to add checking for corrupt files here.
*/
LZWCode = ReadCode();
while (LZWCode != EOFCode) {
/* Clear code sets everything back to its initial value, then reads the
* immediately subsequent code as uncompressed data.
*/
if (LZWCode == ClearCode) {
CodeSize = InitCodeSize;
MaxCode = (1 << CodeSize);
ReadMask = MaxCode - 1;
FreeCode = FirstFree;
CurCode = OldCode = LZWCode = ReadCode();
FinChar = CurCode & BitMask;
AddToPixel(FinChar);
} else {
/* If not a clear code, then must be data: save same as CurCode and InCode */
CurCode = InCode = LZWCode;
/* If greater or equal to FreeCode, not in the hash table yet;
* repeat the last character decoded
*/
if (CurCode >= FreeCode) {
CurCode = OldCode;
OutCode[OutCount++] = FinChar;
}
/* Unless this code is raw data, pursue the chain pointed to by CurCode
* through the hash table to its end; each code in the chain puts its
* associated output code on the output queue.
*/
while (CurCode > BitMask) {
if (OutCount > 1024) {
fprintf(stderr, "%s is a corrupt GIF file (OutCount).\n",
im->name);
goto error_exit;
}
OutCode[OutCount++] = Suffix[CurCode];
CurCode = Prefix[CurCode];
}
/* The last code in the chain is treated as raw data. */
FinChar = CurCode & BitMask;
OutCode[OutCount++] = FinChar;
/* Now we put the data out to the Output routine.
* It's been stacked LIFO, so deal with it that way...
*/
for (i = OutCount - 1; i >= 0; i--)
AddToPixel(OutCode[i]);
OutCount = 0;
/* Build the hash table on-the-fly. No table is stored in the file. */
Prefix[FreeCode] = OldCode;
Suffix[FreeCode] = FinChar;
OldCode = InCode;
/* Point to the next slot in the table. If we exceed the current
* MaxCode value, increment the code size unless it's already 12. If it
* is, do nothing: the next code decompressed better be CLEAR
*/
FreeCode++;
if (FreeCode >= MaxCode) {
if (CodeSize < 12) {
CodeSize++;
MaxCode *= 2;
ReadMask = (1 << CodeSize) - 1;
}
}
}
LZWCode = ReadCode();
}
error_exit:
free(Raster);
im->w = Width;
im->h = Height;
im->d = 8;
xim = XCreateImage(dsp, vis, im->d, ZPixmap, 0, Image,
im->w, im->h, 8, im->w);
im->pix = XCreatePixmap(dsp, win, im->w, im->h, 8);
XPutImage(dsp, im->pix, gc, xim, 0, 0, 0, 0, im->w, im->h);
XSync(dsp, False);
free(Image);
return im;
}