gifdec.c
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1 /*
2  * GIF decoder
3  * Copyright (c) 2003 Fabrice Bellard
4  * Copyright (c) 2006 Baptiste Coudurier
5  *
6  * This file is part of Libav.
7  *
8  * Libav is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * Libav is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with Libav; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 //#define DEBUG
24 
25 #include "libavutil/imgutils.h"
26 #include "avcodec.h"
27 #include "bytestream.h"
28 #include "internal.h"
29 #include "lzw.h"
30 
31 #define GCE_DISPOSAL_NONE 0
32 #define GCE_DISPOSAL_INPLACE 1
33 #define GCE_DISPOSAL_BACKGROUND 2
34 #define GCE_DISPOSAL_RESTORE 3
35 
36 typedef struct GifState {
44  uint32_t *image_palette;
45 
46  /* after the frame is displayed, the disposal method is used */
48  /* delay during which the frame is shown */
49  int gce_delay;
50 
51  /* LZW compatible decoder */
55 
56  /* aux buffers */
59 
61 } GifState;
62 
63 static const uint8_t gif87a_sig[6] = "GIF87a";
64 static const uint8_t gif89a_sig[6] = "GIF89a";
65 
66 static int gif_read_image(GifState *s)
67 {
68  int left, top, width, height, bits_per_pixel, code_size, flags;
69  int is_interleaved, has_local_palette, y, pass, y1, linesize, n, i;
70  uint8_t *ptr, *spal, *palette, *ptr1;
71 
72  left = bytestream_get_le16(&s->bytestream);
73  top = bytestream_get_le16(&s->bytestream);
74  width = bytestream_get_le16(&s->bytestream);
75  height = bytestream_get_le16(&s->bytestream);
76  flags = bytestream_get_byte(&s->bytestream);
77  is_interleaved = flags & 0x40;
78  has_local_palette = flags & 0x80;
79  bits_per_pixel = (flags & 0x07) + 1;
80 
81  av_dlog(s->avctx, "gif: image x=%d y=%d w=%d h=%d\n", left, top, width, height);
82 
83  if (has_local_palette) {
84  bytestream_get_buffer(&s->bytestream, s->local_palette, 3 * (1 << bits_per_pixel));
85  palette = s->local_palette;
86  } else {
87  palette = s->global_palette;
88  bits_per_pixel = s->bits_per_pixel;
89  }
90 
91  /* verify that all the image is inside the screen dimensions */
92  if (left + width > s->screen_width ||
93  top + height > s->screen_height)
94  return AVERROR(EINVAL);
95 
96  /* build the palette */
97  n = (1 << bits_per_pixel);
98  spal = palette;
99  for(i = 0; i < n; i++) {
100  s->image_palette[i] = (0xffu << 24) | AV_RB24(spal);
101  spal += 3;
102  }
103  for(; i < 256; i++)
104  s->image_palette[i] = (0xffu << 24);
105  /* handle transparency */
106  if (s->transparent_color_index >= 0)
108 
109  /* now get the image data */
110  code_size = bytestream_get_byte(&s->bytestream);
111  ff_lzw_decode_init(s->lzw, code_size, s->bytestream,
113 
114  /* read all the image */
115  linesize = s->picture.linesize[0];
116  ptr1 = s->picture.data[0] + top * linesize + left;
117  ptr = ptr1;
118  pass = 0;
119  y1 = 0;
120  for (y = 0; y < height; y++) {
121  ff_lzw_decode(s->lzw, ptr, width);
122  if (is_interleaved) {
123  switch(pass) {
124  default:
125  case 0:
126  case 1:
127  y1 += 8;
128  ptr += linesize * 8;
129  if (y1 >= height) {
130  y1 = pass ? 2 : 4;
131  ptr = ptr1 + linesize * y1;
132  pass++;
133  }
134  break;
135  case 2:
136  y1 += 4;
137  ptr += linesize * 4;
138  if (y1 >= height) {
139  y1 = 1;
140  ptr = ptr1 + linesize;
141  pass++;
142  }
143  break;
144  case 3:
145  y1 += 2;
146  ptr += linesize * 2;
147  break;
148  }
149  } else {
150  ptr += linesize;
151  }
152  }
153  /* read the garbage data until end marker is found */
155  s->bytestream = ff_lzw_cur_ptr(s->lzw);
156  return 0;
157 }
158 
160 {
161  int ext_code, ext_len, i, gce_flags, gce_transparent_index;
162 
163  /* extension */
164  ext_code = bytestream_get_byte(&s->bytestream);
165  ext_len = bytestream_get_byte(&s->bytestream);
166 
167  av_dlog(s->avctx, "gif: ext_code=0x%x len=%d\n", ext_code, ext_len);
168 
169  switch(ext_code) {
170  case 0xf9:
171  if (ext_len != 4)
172  goto discard_ext;
173  s->transparent_color_index = -1;
174  gce_flags = bytestream_get_byte(&s->bytestream);
175  s->gce_delay = bytestream_get_le16(&s->bytestream);
176  gce_transparent_index = bytestream_get_byte(&s->bytestream);
177  if (gce_flags & 0x01)
178  s->transparent_color_index = gce_transparent_index;
179  else
180  s->transparent_color_index = -1;
181  s->gce_disposal = (gce_flags >> 2) & 0x7;
182 
183  av_dlog(s->avctx, "gif: gce_flags=%x delay=%d tcolor=%d disposal=%d\n",
184  gce_flags, s->gce_delay,
186 
187  ext_len = bytestream_get_byte(&s->bytestream);
188  break;
189  }
190 
191  /* NOTE: many extension blocks can come after */
192  discard_ext:
193  while (ext_len != 0) {
194  for (i = 0; i < ext_len; i++)
195  bytestream_get_byte(&s->bytestream);
196  ext_len = bytestream_get_byte(&s->bytestream);
197 
198  av_dlog(s->avctx, "gif: ext_len1=%d\n", ext_len);
199  }
200  return 0;
201 }
202 
204 {
205  uint8_t sig[6];
206  int v, n;
207  int has_global_palette;
208 
209  if (s->bytestream_end < s->bytestream + 13)
210  return -1;
211 
212  /* read gif signature */
213  bytestream_get_buffer(&s->bytestream, sig, 6);
214  if (memcmp(sig, gif87a_sig, 6) != 0 &&
215  memcmp(sig, gif89a_sig, 6) != 0)
216  return -1;
217 
218  /* read screen header */
219  s->transparent_color_index = -1;
220  s->screen_width = bytestream_get_le16(&s->bytestream);
221  s->screen_height = bytestream_get_le16(&s->bytestream);
222  if( (unsigned)s->screen_width > 32767
223  || (unsigned)s->screen_height > 32767){
224  av_log(NULL, AV_LOG_ERROR, "picture size too large\n");
225  return -1;
226  }
227 
228  v = bytestream_get_byte(&s->bytestream);
229  s->color_resolution = ((v & 0x70) >> 4) + 1;
230  has_global_palette = (v & 0x80);
231  s->bits_per_pixel = (v & 0x07) + 1;
232  s->background_color_index = bytestream_get_byte(&s->bytestream);
233  bytestream_get_byte(&s->bytestream); /* ignored */
234 
235  av_dlog(s->avctx, "gif: screen_w=%d screen_h=%d bpp=%d global_palette=%d\n",
237  has_global_palette);
238 
239  if (has_global_palette) {
240  n = 1 << s->bits_per_pixel;
241  if (s->bytestream_end < s->bytestream + n * 3)
242  return -1;
244  }
245  return 0;
246 }
247 
249 {
250  while (s->bytestream < s->bytestream_end) {
251  int code = bytestream_get_byte(&s->bytestream);
252 
253  av_dlog(s->avctx, "gif: code=%02x '%c'\n", code, code);
254 
255  switch (code) {
256  case ',':
257  return gif_read_image(s);
258  case '!':
259  if (gif_read_extension(s) < 0)
260  return -1;
261  break;
262  case ';':
263  /* end of image */
264  default:
265  /* error or erroneous EOF */
266  return -1;
267  }
268  }
269  return -1;
270 }
271 
273 {
274  GifState *s = avctx->priv_data;
275 
276  s->avctx = avctx;
277 
279  avctx->coded_frame= &s->picture;
280  s->picture.data[0] = NULL;
281  ff_lzw_decode_open(&s->lzw);
282  return 0;
283 }
284 
285 static int gif_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
286  AVPacket *avpkt)
287 {
288  const uint8_t *buf = avpkt->data;
289  int buf_size = avpkt->size;
290  GifState *s = avctx->priv_data;
291  AVFrame *picture = data;
292  int ret;
293 
294  s->bytestream = buf;
295  s->bytestream_end = buf + buf_size;
296  if (gif_read_header1(s) < 0)
297  return -1;
298 
299  avctx->pix_fmt = AV_PIX_FMT_PAL8;
300  if (av_image_check_size(s->screen_width, s->screen_height, 0, avctx))
301  return -1;
303 
304  if (s->picture.data[0])
305  avctx->release_buffer(avctx, &s->picture);
306  if (ff_get_buffer(avctx, &s->picture) < 0) {
307  av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
308  return -1;
309  }
310  s->image_palette = (uint32_t *)s->picture.data[1];
311  ret = gif_parse_next_image(s);
312  if (ret < 0)
313  return ret;
314 
315  *picture = s->picture;
316  *got_frame = 1;
317  return s->bytestream - buf;
318 }
319 
321 {
322  GifState *s = avctx->priv_data;
323 
325  if(s->picture.data[0])
326  avctx->release_buffer(avctx, &s->picture);
327  return 0;
328 }
329 
331  .name = "gif",
332  .type = AVMEDIA_TYPE_VIDEO,
333  .id = AV_CODEC_ID_GIF,
334  .priv_data_size = sizeof(GifState),
338  .capabilities = CODEC_CAP_DR1,
339  .long_name = NULL_IF_CONFIG_SMALL("GIF (Graphics Interchange Format)"),
340 };