1 const char deanimate_rcs[] = "$Id: deanimate.c,v 1.2 2001/07/13 13:46:20 oes Exp $";
2 /*********************************************************************
4 * File : $Source: /cvsroot/ijbswa/current/deanimate.c,v $
6 * Purpose : Declares functions to deanimate GIF images on the fly.
8 * Functions declared include: gif_deanimate, buf_free,
9 * buf_copy, buf_getbyte, gif_skip_data_block, and
12 * Copyright : Written by and Copyright (C) 2001 Andreas S. Oesterhelt
13 * for the SourceForge IJBSWA team. http://ijbswa.sourceforge.net
15 * Based on the GIF file format specification (see
16 * http://tronche.com/computer-graphics/gif/gif89a.html)
17 * and ideas from the Image::DeAnim Perl module by
18 * Ken MacFarlane, <ksm+cpan@universal.dca.net>
20 * This program is free software; you can redistribute it
21 * and/or modify it under the terms of the GNU General
22 * Public License as published by the Free Software
23 * Foundation; either version 2 of the License, or (at
24 * your option) any later version.
26 * This program is distributed in the hope that it will
27 * be useful, but WITHOUT ANY WARRANTY; without even the
28 * implied warranty of MERCHANTABILITY or FITNESS FOR A
29 * PARTICULAR PURPOSE. See the GNU General Public
30 * License for more details.
32 * The GNU General Public License should be included with
33 * this file. If not, you can view it at
34 * http://www.gnu.org/copyleft/gpl.html
35 * or write to the Free Software Foundation, Inc., 59
36 * Temple Place - Suite 330, Boston, MA 02111-1307, USA.
39 * $Log: deanimate.c,v $
40 * Revision 1.2 2001/07/13 13:46:20 oes
41 * Introduced GIF deanimation feature
44 **********************************************************************/
53 #include "deanimate.h"
56 const char deanimate_h_rcs[] = DEANIMATE_H_VERSION;
58 /*********************************************************************
62 * Description : Safely frees a struct binbuffer
65 * 1 : buf = Pointer to the binbuffer to be freed
69 *********************************************************************/
70 void buf_free(struct binbuffer *buf)
72 if (buf == NULL) return;
74 if (buf->buffer != NULL)
84 /*********************************************************************
88 * Description : Safely copies a given amount of bytes from one
89 * struct binbuffer to another, advancing the
90 * offsets appropriately.
93 * 1 : src = Pointer to the source binbuffer
94 * 2 : dst = Pointer to the destination binbuffer
95 * 3 : length = Number of bytes to be copied
97 * Returns : 0 on success, 1 on failiure.
99 *********************************************************************/
100 int buf_copy(struct binbuffer *src, struct binbuffer *dst, int length)
105 * Sanity check: Can't copy more data than we have
107 if (src->offset + length > src->size)
113 * If dst can't hold the new data, get mem first. (In chunks
114 * of 1000 bytes, so we don't have to realloc() too often)
116 if (dst->offset + length > dst->size)
118 dst->size = dst->size + length + 1000 - (dst->size + length) % 1000;
120 dst->buffer = (char *)realloc(dst->buffer, dst->size);
122 if (dst->buffer == NULL)
130 * Now that it's safe, memcpy() the desired amount of
131 * data from src to dst and adjust the offsets
133 memcpy(dst->buffer + dst->offset, src->buffer + src->offset, length);
134 src->offset += length;
135 dst->offset += length;
142 /*********************************************************************
144 * Function : buf_getbyte
146 * Description : Safely gets a byte from a given binbuffer at a
150 * 1 : buf = Pointer to the source binbuffer
151 * 2 : offset = Offset to the desired byte
153 * Returns : The byte on success, or 0 on failiure
155 *********************************************************************/
156 unsigned char buf_getbyte(struct binbuffer *src, int offset)
158 if (src->offset + offset < src->size)
160 return (unsigned char)*(src->buffer + src->offset + offset);
170 /*********************************************************************
172 * Function : gif_skip_data_block
174 * Description : Safely advances the offset of a given struct binbuffer
175 * that contains a GIF image and whose offset is
176 * positioned at the start of a data block behind
180 * 1 : buf = Pointer to the binbuffer
182 * Returns : 0 on success, or 1 on failiure
184 *********************************************************************/
185 int gif_skip_data_block(struct binbuffer *buf)
190 * Data blocks are sequences of chunks, which are headed
191 * by a one-byte length field, with the last chunk having
194 while(c = buf_getbyte(buf, 0))
196 if ((buf->offset += c + 1) >= buf->size - 1)
208 /*********************************************************************
210 * Function : gif_extract_image
212 * Description : Safely extracts an image data block from a given
213 * struct binbuffer that contains a GIF image and whose
214 * offset is positioned at the start of a data block
215 * into a given destination binbuffer.
218 * 1 : src = Pointer to the source binbuffer
219 * 2 : dst = Pointer to the destination binbuffer
221 * Returns : 0 on success, or 1 on failiure
223 *********************************************************************/
224 int gif_extract_image(struct binbuffer *src, struct binbuffer *dst)
229 * Remember the colormap flag and copy the image head
231 c = buf_getbyte(src, 9);
232 if (buf_copy(src, dst, 10))
238 * If the image has a local colormap, copy it.
242 if (buf_copy(src, dst, 3 * (1 << ((c & 0x07) + 1))))
247 if (buf_copy(src, dst, 1)) return 1;
250 * Copy the image chunk by chunk.
252 while(c = buf_getbyte(src, 0))
254 if (buf_copy(src, dst, c + 1)) return 1;
256 if (buf_copy(src, dst, 1)) return 1;
259 * Trim and rewind the dst buffer
261 dst->buffer = (char *)realloc(dst->buffer, dst->offset);
262 dst->size = dst->offset;
269 /*********************************************************************
271 * Function : gif_deanimate
273 * Description : Deanimate a given GIF image, i.e. given a GIF with
274 * an (optional) image block and an arbitrary number
275 * of image extension blocks, produce an output GIF with
276 * only one image block that contains the last image
277 * (extenstion) block of the original.
278 * Also strip Comments, Application extenstions, etc.
281 * 1 : src = Pointer to the source binbuffer
282 * 2 : dst = Pointer to the destination binbuffer
284 * Returns : 0 on success, or 1 on failiure
286 *********************************************************************/
287 int gif_deanimate(struct binbuffer *src, struct binbuffer *dst)
290 struct binbuffer *image;
292 if (NULL == src || NULL == dst)
297 c = buf_getbyte(src, 10);
300 * Check & copy GIF header
302 if (strncmp(src->buffer, "GIF89a", 6))
304 fprintf(stderr, "This is not a GIF98a!\n");
309 if (buf_copy(src, dst, 13))
316 * Look for global colormap and copy if found.
320 if (buf_copy(src, dst, 3 * (1 << ((c & 0x07) + 1))))
327 * Reserve a buffer for the current image block
329 if (NULL == (image = (struct binbuffer *)zalloc(sizeof(*image))))
335 * Parse the GIF block by block and copy the relevant
338 while(src->offset < src->size)
340 switch(buf_getbyte(src, 0))
343 * End-of-GIF Marker: Append current image and return
346 if (buf_copy(image, dst, image->size) || buf_copy(src, dst, 1))
354 * Image block: Extract to current image buffer
358 if (gif_extract_image(src, image))
365 * Extension block: Look at next byte and decide
368 switch (buf_getbyte(src, 1))
371 * Image extension: Copy extension header and image
372 * to the current image buffer
376 if (buf_copy(src, image, 8) || buf_getbyte(src, 0) != 0x2c) goto failed;
377 if (gif_extract_image(src, image)) goto failed;
381 * Application extension: Skip
384 if ((src->offset += 14) >= src->size || gif_skip_data_block(src)) goto failed;
388 * Comment extension: Skip
391 if ((src->offset += 2) >= src->size || gif_skip_data_block(src)) goto failed;
395 * Plain text extension: Skip
398 if ((src->offset += 15) >= src->size || gif_skip_data_block(src)) goto failed;
402 * Ooops, what type of extension is that?
410 * Ooops, what type of block is that?
416 } /* -END- while src */
419 * Either we got here by goto, or because the GIF is
420 * bogus and EOF was reached before an end-of-gif marker