static int gif_read_image(GifState *s) { int left, top, width, height, bits_per_pixel, code_size, flags; int is_interleaved, has_local_palette, y, pass, y1, linesize, n, i; uint8_t *ptr, *spal, *palette, *ptr1; left = bytestream_get_le16(&s->bytestream); top = bytestream_get_le16(&s->bytestream); width = bytestream_get_le16(&s->bytestream); height = bytestream_get_le16(&s->bytestream); flags = bytestream_get_byte(&s->bytestream); is_interleaved = flags & 0x40; has_local_palette = flags & 0x80; bits_per_pixel = (flags & 0x07) + 1; av_dlog(s->avctx, "image x=%d y=%d w=%d h=%d\n", left, top, width, height); if (has_local_palette) { bytestream_get_buffer(&s->bytestream, 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 AVERROR(EINVAL); /* build the palette */ n = (1 << bits_per_pixel); spal = palette; for(i = 0; i < n; i++) { s->image_palette[i] = (0xffu << 24) | AV_RB24(spal); spal += 3; } for(; i < 256; i++) s->image_palette[i] = (0xffu << 24); /* handle transparency */ if (s->transparent_color_index >= 0) s->image_palette[s->transparent_color_index] = 0; /* now get the image data */ code_size = bytestream_get_byte(&s->bytestream); ff_lzw_decode_init(s->lzw, code_size, s->bytestream, s->bytestream_end - s->bytestream, FF_LZW_GIF); /* read all the image */ linesize = s->picture.linesize[0]; ptr1 = s->picture.data[0] + top * linesize + left; ptr = ptr1; pass = 0; y1 = 0; for (y = 0; y < height; y++) { ff_lzw_decode(s->lzw, ptr, width); if (is_interleaved) { switch(pass) { default: case 0: case 1: y1 += 8; ptr += linesize * 8; if (y1 >= height) { y1 = pass ? 2 : 4; ptr = ptr1 + linesize * y1; 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; } } /* read the garbage data until end marker is found */ ff_lzw_decode_tail(s->lzw); s->bytestream = ff_lzw_cur_ptr(s->lzw); return 0; }