gifdec.c

FFmpeg is an audio/video conversion tool. It includes libavcodec, the leading open source codec libr

/*
 * 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)