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FFmpeg/libavformat/gifdec.c
Fabrice Bellard a059da1227 transparency support 
Originally committed as revision 1808 to svn://svn.ffmpeg.org/ffmpeg/trunk
2003-04-21 21:18:51 +00:00

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/*
* GIF decoder
* Copyright (c) 2003 Fabrice Bellard.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "avformat.h"
int gif_write(ByteIOContext *pb, AVImageInfo *info);
//#define DEBUG
#define MAXBITS 12
#define SIZTABLE (1<<MAXBITS)
#define GCE_DISPOSAL_NONE 0
#define GCE_DISPOSAL_INPLACE 1
#define GCE_DISPOSAL_BACKGROUND 2
#define GCE_DISPOSAL_RESTORE 3
typedef struct GifState {
int screen_width;
int screen_height;
int bits_per_pixel;
int background_color_index;
int transparent_color_index;
int color_resolution;
uint8_t *image_buf;
int image_linesize;
uint32_t *image_palette;
int pix_fmt;
/* after the frame is displayed, the disposal method is used */
int gce_disposal;
/* delay during which the frame is shown */
int gce_delay;
/* LZW compatible decoder */
ByteIOContext *f;
int eob_reached;
uint8_t *pbuf, *ebuf;
int bbits;
unsigned int bbuf;
int cursize; /* The current code size */
int curmask;
int codesize;
int clear_code;
int end_code;
int newcodes; /* First available code */
int top_slot; /* Highest code for current size */
int slot; /* Last read code */
int fc, oc;
uint8_t *sp;
uint8_t stack[SIZTABLE];
uint8_t suffix[SIZTABLE];
uint16_t prefix[SIZTABLE];
/* aux buffers */
uint8_t global_palette[256 * 3];
uint8_t local_palette[256 * 3];
uint8_t buf[256];
} GifState;
static const uint8_t gif87a_sig[6] = "GIF87a";
static const uint8_t gif89a_sig[6] = "GIF89a";
static const uint16_t mask[17] =
{
0x0000, 0x0001, 0x0003, 0x0007,
0x000F, 0x001F, 0x003F, 0x007F,
0x00FF, 0x01FF, 0x03FF, 0x07FF,
0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
};
/* Probe gif video format or gif image format. The current heuristic
supposes the gif87a is always a single image. For gif89a, we
consider it as a video only if a GCE extension is present in the
first kilobyte. */
static int gif_video_probe(AVProbeData * pd)
{
const uint8_t *p, *p_end;
int bits_per_pixel, has_global_palette, ext_code, ext_len;
int gce_flags, gce_disposal;
if (pd->buf_size < 24 ||
memcmp(pd->buf, gif89a_sig, 6) != 0)
return 0;
p_end = pd->buf + pd->buf_size;
p = pd->buf + 6;
bits_per_pixel = (p[4] & 0x07) + 1;
has_global_palette = (p[4] & 0x80);
p += 7;
if (has_global_palette)
p += (1 << bits_per_pixel) * 3;
for(;;) {
if (p >= p_end)
return 0;
if (*p != '!')
break;
p++;
if (p >= p_end)
return 0;
ext_code = *p++;
if (p >= p_end)
return 0;
ext_len = *p++;
if (ext_code == 0xf9) {
if (p >= p_end)
return 0;
/* if GCE extension found with gce_disposal != 0: it is
likely to be an animation */
gce_flags = *p++;
gce_disposal = (gce_flags >> 2) & 0x7;
if (gce_disposal != 0)
return AVPROBE_SCORE_MAX;
else
return 0;
}
for(;;) {
if (ext_len == 0)
break;
p += ext_len;
if (p >= p_end)
return 0;
ext_len = *p++;
}
}
return 0;
}
static int gif_image_probe(AVProbeData * pd)
{
if (pd->buf_size >= 24 &&
(memcmp(pd->buf, gif87a_sig, 6) == 0 ||
memcmp(pd->buf, gif89a_sig, 6) == 0))
return AVPROBE_SCORE_MAX - 1;
else
return 0;
}
static void GLZWDecodeInit(GifState * s, int csize)
{
/* read buffer */
s->eob_reached = 0;
s->pbuf = s->buf;
s->ebuf = s->buf;
s->bbuf = 0;
s->bbits = 0;
/* decoder */
s->codesize = csize;
s->cursize = s->codesize + 1;
s->curmask = mask[s->cursize];
s->top_slot = 1 << s->cursize;
s->clear_code = 1 << s->codesize;
s->end_code = s->clear_code + 1;
s->slot = s->newcodes = s->clear_code + 2;
s->oc = s->fc = 0;
s->sp = s->stack;
}
/* XXX: optimize */
static inline int GetCode(GifState * s)
{
int c, sizbuf;
uint8_t *ptr;
while (s->bbits < s->cursize) {
ptr = s->pbuf;
if (ptr >= s->ebuf) {
if (!s->eob_reached) {
sizbuf = get_byte(s->f);
s->ebuf = s->buf + sizbuf;
s->pbuf = s->buf;
if (sizbuf > 0) {
get_buffer(s->f, s->buf, sizbuf);
} else {
s->eob_reached = 1;
}
}
ptr = s->pbuf;
}
s->bbuf |= ptr[0] << s->bbits;
ptr++;
s->pbuf = ptr;
s->bbits += 8;
}
c = s->bbuf & s->curmask;
s->bbuf >>= s->cursize;
s->bbits -= s->cursize;
return c;
}
/* NOTE: the algorithm here is inspired from the LZW GIF decoder
written by Steven A. Bennett in 1987. */
/* return the number of byte decoded */
static int GLZWDecode(GifState * s, uint8_t * buf, int len)
{
int l, c, code, oc, fc;
uint8_t *sp;
if (s->end_code < 0)
return 0;
l = len;
sp = s->sp;
oc = s->oc;
fc = s->fc;
while (sp > s->stack) {
*buf++ = *(--sp);
if ((--l) == 0)
goto the_end;
}
for (;;) {
c = GetCode(s);
if (c == s->end_code) {
s->end_code = -1;
break;
} else if (c == s->clear_code) {
s->cursize = s->codesize + 1;
s->curmask = mask[s->cursize];
s->slot = s->newcodes;
s->top_slot = 1 << s->cursize;
while ((c = GetCode(s)) == s->clear_code);
if (c == s->end_code) {
s->end_code = -1;
break;
}
/* test error */
if (c >= s->slot)
c = 0;
fc = oc = c;
*buf++ = c;
if ((--l) == 0)
break;
} else {
code = c;
if (code >= s->slot) {
*sp++ = fc;
code = oc;
}
while (code >= s->newcodes) {
*sp++ = s->suffix[code];
code = s->prefix[code];
}
*sp++ = code;
if (s->slot < s->top_slot) {
s->suffix[s->slot] = fc = code;
s->prefix[s->slot++] = oc;
oc = c;
}
if (s->slot >= s->top_slot) {
if (s->cursize < MAXBITS) {
s->top_slot <<= 1;
s->curmask = mask[++s->cursize];
}
}
while (sp > s->stack) {
*buf++ = *(--sp);
if ((--l) == 0)
goto the_end;
}
}
}
the_end:
s->sp = sp;
s->oc = oc;
s->fc = fc;
return len - l;
}
static int gif_read_image(GifState *s)
{
ByteIOContext *f = s->f;
int left, top, width, height, bits_per_pixel, code_size, flags;
int is_interleaved, has_local_palette, y, x, pass, y1, linesize, n, i;
uint8_t *ptr, *line, *d, *spal, *palette, *sptr, *ptr1;
left = get_le16(f);
top = get_le16(f);
width = get_le16(f);
height = get_le16(f);
flags = get_byte(f);
is_interleaved = flags & 0x40;
has_local_palette = flags & 0x80;
bits_per_pixel = (flags & 0x07) + 1;
#ifdef DEBUG
printf("gif: image x=%d y=%d w=%d h=%d\n", left, top, width, height);
#endif
if (has_local_palette) {
get_buffer(f, s->local_palette, 3 * (1 << bits_per_pixel));
palette = s->local_palette;
} else {
palette = s->global_palette;
bits_per_pixel = s->bits_per_pixel;
}
/* verify that all the image is inside the screen dimensions */
if (left + width > s->screen_width ||
top + height > s->screen_height)
return -EINVAL;
/* build the palette */
if (s->pix_fmt == PIX_FMT_RGB24) {
line = av_malloc(width);
if (!line)
return -ENOMEM;
} else {
n = (1 << bits_per_pixel);
spal = palette;
for(i = 0; i < n; i++) {
s->image_palette[i] = (0xff << 24) |
(spal[0] << 16) | (spal[1] << 8) | (spal[2]);
spal += 3;
}
for(; i < 256; i++)
s->image_palette[i] = (0xff << 24);
/* handle transparency */
if (s->transparent_color_index >= 0)
s->image_palette[s->transparent_color_index] = 0;
line = NULL;
}
/* now get the image data */
s->f = f;
code_size = get_byte(f);
GLZWDecodeInit(s, code_size);
/* read all the image */
linesize = s->image_linesize;
ptr1 = s->image_buf + top * linesize + (left * 3);
ptr = ptr1;
pass = 0;
y1 = 0;
for (y = 0; y < height; y++) {
if (s->pix_fmt == PIX_FMT_RGB24) {
/* transcode to RGB24 */
GLZWDecode(s, line, width);
d = ptr;
sptr = line;
for(x = 0; x < width; x++) {
spal = palette + sptr[0] * 3;
d[0] = spal[0];
d[1] = spal[1];
d[2] = spal[2];
d += 3;
sptr++;
}
} else {
GLZWDecode(s, ptr, width);
}
if (is_interleaved) {
switch(pass) {
default:
case 0:
case 1:
y1 += 8;
ptr += linesize * 8;
if (y1 >= height) {
y1 = 4;
if (pass == 0)
ptr = ptr1 + linesize * 4;
else
ptr = ptr1 + linesize * 2;
pass++;
}
break;
case 2:
y1 += 4;
ptr += linesize * 4;
if (y1 >= height) {
y1 = 1;
ptr = ptr1 + linesize;
pass++;
}
break;
case 3:
y1 += 2;
ptr += linesize * 2;
break;
}
} else {
ptr += linesize;
}
}
av_free(line);
/* read the garbage data until end marker is found */
while (!s->eob_reached)
GetCode(s);
return 0;
}
static int gif_read_extension(GifState *s)
{
ByteIOContext *f = s->f;
int ext_code, ext_len, i, gce_flags, gce_transparent_index;
/* extension */
ext_code = get_byte(f);
ext_len = get_byte(f);
#ifdef DEBUG
printf("gif: ext_code=0x%x len=%d\n", ext_code, ext_len);
#endif
switch(ext_code) {
case 0xf9:
if (ext_len != 4)
goto discard_ext;
s->transparent_color_index = -1;
gce_flags = get_byte(f);
s->gce_delay = get_le16(f);
gce_transparent_index = get_byte(f);
if (gce_flags & 0x01)
s->transparent_color_index = gce_transparent_index;
else
s->transparent_color_index = -1;
s->gce_disposal = (gce_flags >> 2) & 0x7;
#ifdef DEBUG
printf("gif: gce_flags=%x delay=%d tcolor=%d disposal=%d\n",
gce_flags, s->gce_delay,
s->transparent_color_index, s->gce_disposal);
#endif
ext_len = get_byte(f);
break;
}
/* NOTE: many extension blocks can come after */
discard_ext:
while (ext_len != 0) {
for (i = 0; i < ext_len; i++)
get_byte(f);
ext_len = get_byte(f);
#ifdef DEBUG
printf("gif: ext_len1=%d\n", ext_len);
#endif
}
return 0;
}
static int gif_read_header1(GifState *s)
{
ByteIOContext *f = s->f;
uint8_t sig[6];
int ret, v, n;
int has_global_palette;
/* read gif signature */
ret = get_buffer(f, sig, 6);
if (ret != 6)
return -1;
if (memcmp(sig, gif87a_sig, 6) != 0 &&
memcmp(sig, gif89a_sig, 6) != 0)
return -1;
/* read screen header */
s->transparent_color_index = -1;
s->screen_width = get_le16(f);
s->screen_height = get_le16(f);
v = get_byte(f);
s->color_resolution = ((v & 0x70) >> 4) + 1;
has_global_palette = (v & 0x80);
s->bits_per_pixel = (v & 0x07) + 1;
s->background_color_index = get_byte(f);
get_byte(f); /* ignored */
#ifdef DEBUG
printf("gif: screen_w=%d screen_h=%d bpp=%d global_palette=%d\n",
s->screen_width, s->screen_height, s->bits_per_pixel,
has_global_palette);
#endif
if (has_global_palette) {
n = 1 << s->bits_per_pixel;
get_buffer(f, s->global_palette, n * 3);
}
return 0;
}
static int gif_parse_next_image(GifState *s)
{
ByteIOContext *f = s->f;
int ret, code;
for (;;) {
code = url_fgetc(f);
#ifdef DEBUG
printf("gif: code=%02x '%c'\n", code, code);
#endif
switch (code) {
case ',':
if (gif_read_image(s) < 0)
return -EIO;
ret = 0;
goto the_end;
case ';':
/* end of image */
ret = -EIO;
goto the_end;
case '!':
if (gif_read_extension(s) < 0)
return -EIO;
break;
case EOF:
default:
/* error or errneous EOF */
ret = -EIO;
goto the_end;
}
}
the_end:
return ret;
}
static int gif_read_header(AVFormatContext * s1,
AVFormatParameters * ap)
{
GifState *s = s1->priv_data;
ByteIOContext *f = &s1->pb;
AVStream *st;
s->f = f;
if (gif_read_header1(s) < 0)
return -1;
/* allocate image buffer */
s->image_linesize = s->screen_width * 3;
s->image_buf = av_malloc(s->screen_height * s->image_linesize);
if (!s->image_buf)
return -ENOMEM;
s->pix_fmt = PIX_FMT_RGB24;
/* now we are ready: build format streams */
st = av_new_stream(s1, 0);
if (!st)
return -1;
st->codec.codec_type = CODEC_TYPE_VIDEO;
st->codec.codec_id = CODEC_ID_RAWVIDEO;
st->codec.frame_rate = 5;
st->codec.frame_rate_base = 1;
/* XXX: check if screen size is always valid */
st->codec.width = s->screen_width;
st->codec.height = s->screen_height;
st->codec.pix_fmt = PIX_FMT_RGB24;
return 0;
}
static int gif_read_packet(AVFormatContext * s1,
AVPacket * pkt)
{
GifState *s = s1->priv_data;
int ret;
ret = gif_parse_next_image(s);
if (ret < 0)
return ret;
/* XXX: avoid copying */
if (av_new_packet(pkt, s->screen_width * s->screen_height * 3)) {
return -EIO;
}
pkt->stream_index = 0;
memcpy(pkt->data, s->image_buf, s->screen_width * s->screen_height * 3);
return 0;
}
static int gif_read_close(AVFormatContext *s1)
{
GifState *s = s1->priv_data;
av_free(s->image_buf);
return 0;
}
/* read gif as image */
static int gif_read(ByteIOContext *f,
int (*alloc_cb)(void *opaque, AVImageInfo *info), void *opaque)
{
GifState s1, *s = &s1;
AVImageInfo info1, *info = &info1;
int ret;
memset(s, 0, sizeof(GifState));
s->f = f;
if (gif_read_header1(s) < 0)
return -1;
info->width = s->screen_width;
info->height = s->screen_height;
info->pix_fmt = PIX_FMT_PAL8;
ret = alloc_cb(opaque, info);
if (ret)
return ret;
s->image_buf = info->pict.data[0];
s->image_linesize = info->pict.linesize[0];
s->image_palette = (uint32_t *)info->pict.data[1];
if (gif_parse_next_image(s) < 0)
return -1;
return 0;
}
AVInputFormat gif_iformat =
{
"gif",
"gif format",
sizeof(GifState),
gif_video_probe,
gif_read_header,
gif_read_packet,
gif_read_close,
};
AVImageFormat gif_image_format = {
"gif",
"gif",
gif_image_probe,
gif_read,
(1 << PIX_FMT_PAL8),
gif_write,
};
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