pngdec.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

                    }
                }
            }
        }
    the_end: ;
    }
}

static int png_decode_idat(PNGDecContext *s, int length)
{
    int ret;
    s->zstream.avail_in = length;
    s->zstream.next_in = s->bytestream;
    s->bytestream += length;

    if(s->bytestream > s->bytestream_end)
        return -1;

    /* decode one line if possible */
    while (s->zstream.avail_in > 0) {
        ret = inflate(&s->zstream, Z_PARTIAL_FLUSH);
        if (ret != Z_OK && ret != Z_STREAM_END) {
            return -1;
        }
        if (s->zstream.avail_out == 0) {
            if (!(s->state & PNG_ALLIMAGE)) {
                png_handle_row(s);
            }
            s->zstream.avail_out = s->crow_size;
            s->zstream.next_out = s->crow_buf;
        }
    }
    return 0;
}

static int decode_frame(AVCodecContext *avctx,
                        void *data, int *data_size,
                        uint8_t *buf, int buf_size)
{
    PNGDecContext * const s = avctx->priv_data;
    AVFrame *picture = data;
    AVFrame * const p= (AVFrame*)&s->picture;
    uint32_t tag, length;
    int ret, crc;

    s->bytestream_start=
    s->bytestream= buf;
    s->bytestream_end= buf + buf_size;

    /* check signature */
    if (memcmp(s->bytestream, ff_pngsig, 8) != 0)
        return -1;
    s->bytestream+= 8;
    s->y=
    s->state=0;
//    memset(s, 0, sizeof(PNGDecContext));
    /* init the zlib */
    s->zstream.zalloc = ff_png_zalloc;
    s->zstream.zfree = ff_png_zfree;
    s->zstream.opaque = NULL;
    ret = inflateInit(&s->zstream);
    if (ret != Z_OK)
        return -1;
    for(;;) {
        int tag32;
        if (s->bytestream >= s->bytestream_end)
            goto fail;
        length = bytestream_get_be32(&s->bytestream);
        if (length > 0x7fffffff)
            goto fail;
        tag32 = bytestream_get_be32(&s->bytestream);
        tag = bswap_32(tag32);
#ifdef DEBUG
        av_log(avctx, AV_LOG_DEBUG, "png: tag=%c%c%c%c length=%u\n",
               (tag & 0xff),
               ((tag >> 8) & 0xff),
               ((tag >> 16) & 0xff),
               ((tag >> 24) & 0xff), length);
#endif
        switch(tag) {
        case MKTAG('I', 'H', 'D', 'R'):
            if (length != 13)
                goto fail;
            s->width = bytestream_get_be32(&s->bytestream);
            s->height = bytestream_get_be32(&s->bytestream);
            if(avcodec_check_dimensions(avctx, s->width, s->height)){
                s->width= s->height= 0;
                goto fail;
            }
            s->bit_depth = *s->bytestream++;
            s->color_type = *s->bytestream++;
            s->compression_type = *s->bytestream++;
            s->filter_type = *s->bytestream++;
            s->interlace_type = *s->bytestream++;
            crc = bytestream_get_be32(&s->bytestream);
            s->state |= PNG_IHDR;
#ifdef DEBUG
            av_log(avctx, AV_LOG_DEBUG, "width=%d height=%d depth=%d color_type=%d compression_type=%d filter_type=%d interlace_type=%d\n",
                   s->width, s->height, s->bit_depth, s->color_type,
                   s->compression_type, s->filter_type, s->interlace_type);
#endif
            break;
        case MKTAG('I', 'D', 'A', 'T'):
            if (!(s->state & PNG_IHDR))
                goto fail;
            if (!(s->state & PNG_IDAT)) {
                /* init image info */
                avctx->width = s->width;
                avctx->height = s->height;

                s->channels = ff_png_get_nb_channels(s->color_type);
                s->bits_per_pixel = s->bit_depth * s->channels;
                s->bpp = (s->bits_per_pixel + 7) >> 3;
                s->row_size = (avctx->width * s->bits_per_pixel + 7) >> 3;

                if (s->bit_depth == 8 &&
                    s->color_type == PNG_COLOR_TYPE_RGB) {
                    avctx->pix_fmt = PIX_FMT_RGB24;
                } else if (s->bit_depth == 8 &&
                           s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
                    avctx->pix_fmt = PIX_FMT_RGB32;
                } else if (s->bit_depth == 8 &&
                           s->color_type == PNG_COLOR_TYPE_GRAY) {
                    avctx->pix_fmt = PIX_FMT_GRAY8;
                } else if (s->bit_depth == 16 &&
                           s->color_type == PNG_COLOR_TYPE_GRAY) {
                    avctx->pix_fmt = PIX_FMT_GRAY16BE;
                } else if (s->bit_depth == 1 &&
                           s->color_type == PNG_COLOR_TYPE_GRAY) {
                    avctx->pix_fmt = PIX_FMT_MONOBLACK;
                } else if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
                    avctx->pix_fmt = PIX_FMT_PAL8;
                } else {
                    goto fail;
                }
                if(p->data[0])
                    avctx->release_buffer(avctx, p);

                p->reference= 0;
                if(avctx->get_buffer(avctx, p) < 0){
                    av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
                    goto fail;
                }
                p->pict_type= FF_I_TYPE;
                p->key_frame= 1;
                p->interlaced_frame = !!s->interlace_type;

                /* compute the compressed row size */
                if (!s->interlace_type) {
                    s->crow_size = s->row_size + 1;
                } else {
                    s->pass = 0;
                    s->pass_row_size = ff_png_pass_row_size(s->pass,
                                                         s->bits_per_pixel,
                                                         s->width);
                    s->crow_size = s->pass_row_size + 1;
                }
#ifdef DEBUG
                av_log(avctx, AV_LOG_DEBUG, "row_size=%d crow_size =%d\n",
                       s->row_size, s->crow_size);
#endif
                s->image_buf = p->data[0];
                s->image_linesize = p->linesize[0];
                /* copy the palette if needed */
                if (s->color_type == PNG_COLOR_TYPE_PALETTE)
                    memcpy(p->data[1], s->palette, 256 * sizeof(uint32_t));
                /* empty row is used if differencing to the first row */
                s->last_row = av_mallocz(s->row_size);
                if (!s->last_row)
                    goto fail;
                if (s->interlace_type ||
                    s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
                    s->tmp_row = av_malloc(s->row_size);
                    if (!s->tmp_row)
                        goto fail;
                }
                /* compressed row */
                s->crow_buf = av_malloc(s->row_size + 1);
                if (!s->crow_buf)
                    goto fail;
                s->zstream.avail_out = s->crow_size;
                s->zstream.next_out = s->crow_buf;
            }
            s->state |= PNG_IDAT;
            if (png_decode_idat(s, length) < 0)
                goto fail;
            /* skip crc */
            crc = bytestream_get_be32(&s->bytestream);
            break;
        case MKTAG('P', 'L', 'T', 'E'):
            {
                int n, i, r, g, b;

                if ((length % 3) != 0 || length > 256 * 3)
                    goto skip_tag;
                /* read the palette */
                n = length / 3;
                for(i=0;i<n;i++) {
                    r = *s->bytestream++;
                    g = *s->bytestream++;
                    b = *s->bytestream++;
                    s->palette[i] = (0xff << 24) | (r << 16) | (g << 8) | b;
                }
                for(;i<256;i++) {
                    s->palette[i] = (0xff << 24);
                }
                s->state |= PNG_PLTE;
                crc = bytestream_get_be32(&s->bytestream);
            }
            break;
        case MKTAG('t', 'R', 'N', 'S'):
            {
                int v, i;

                /* read the transparency. XXX: Only palette mode supported */
                if (s->color_type != PNG_COLOR_TYPE_PALETTE ||
                    length > 256 ||
                    !(s->state & PNG_PLTE))
                    goto skip_tag;
                for(i=0;i<length;i++) {
                    v = *s->bytestream++;
                    s->palette[i] = (s->palette[i] & 0x00ffffff) | (v << 24);
                }
                crc = bytestream_get_be32(&s->bytestream);
            }
            break;
        case MKTAG('I', 'E', 'N', 'D'):
            if (!(s->state & PNG_ALLIMAGE))
                goto fail;
            crc = bytestream_get_be32(&s->bytestream);
            goto exit_loop;
        default:
            /* skip tag */
        skip_tag:
            s->bytestream += length + 4;
            break;
        }
    }
 exit_loop:
    *picture= *(AVFrame*)&s->picture;
    *data_size = sizeof(AVPicture);

    ret = s->bytestream - s->bytestream_start;
 the_end:
    inflateEnd(&s->zstream);
    av_freep(&s->crow_buf);
    av_freep(&s->last_row);
    av_freep(&s->tmp_row);
    return ret;
 fail:
    ret = -1;
    goto the_end;
}

static int png_dec_init(AVCodecContext *avctx){
    PNGDecContext *s = avctx->priv_data;

    avcodec_get_frame_defaults((AVFrame*)&s->picture);
    avctx->coded_frame= (AVFrame*)&s->picture;

    return 0;
}

AVCodec png_decoder = {
    "png",
    CODEC_TYPE_VIDEO,
    CODEC_ID_PNG,
    sizeof(PNGDecContext),
    png_dec_init,
    NULL,
    NULL, //decode_end,
    decode_frame,
    0 /*CODEC_CAP_DR1*/ /*| CODEC_CAP_DRAW_HORIZ_BAND*/,
    NULL
};