pngdec.c

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/*
 * PNG image format
 * Copyright (c) 2003 Fabrice Bellard
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg 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 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg 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 FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
 
//#define DEBUG
 
#include "config_components.h"
 
#include "libavutil/avassert.h"
#include "libavutil/bprint.h"
#include "libavutil/crc.h"
#include "libavutil/csp.h"
#include "libavutil/imgutils.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/pixfmt.h"
#include "libavutil/rational.h"
#include "libavutil/stereo3d.h"
 
#include "avcodec.h"
#include "bytestream.h"
#include "codec_internal.h"
#include "decode.h"
#include "apng.h"
#include "png.h"
#include "pngdsp.h"
#include "thread.h"
#include "threadframe.h"
#include "zlib_wrapper.h"
 
#include <zlib.h>
 
enum PNGHeaderState {
    PNG_IHDR = 1 << 0,
    PNG_PLTE = 1 << 1,
};
 
enum PNGImageState {
    PNG_IDAT     = 1 << 0,
    PNG_ALLIMAGE = 1 << 1,
};
 
typedef struct PNGDecContext {
    PNGDSPContext dsp;
    AVCodecContext *avctx;
 
    GetByteContext gb;
    ThreadFrame last_picture;
    ThreadFrame picture;
 
    AVDictionary *frame_metadata;
 
    uint8_t  iccp_name[82];
    uint8_t *iccp_data;
    size_t   iccp_data_len;
 
    int stereo_mode;
 
    int have_chrm;
    uint32_t white_point[2];
    uint32_t display_primaries[3][2];
    int gamma;
    int have_srgb;
    int have_cicp;
    enum AVColorPrimaries cicp_primaries;
    enum AVColorTransferCharacteristic cicp_trc;
    enum AVColorRange cicp_range;
 
    enum PNGHeaderState hdr_state;
    enum PNGImageState pic_state;
    int width, height;
    int cur_w, cur_h;
    int x_offset, y_offset;
    uint8_t dispose_op, blend_op;
    int bit_depth;
    int color_type;
    int compression_type;
    int interlace_type;
    int filter_type;
    int channels;
    int bits_per_pixel;
    int bpp;
    int has_trns;
    uint8_t transparent_color_be[6];
    int significant_bits;
 
    uint32_t palette[256];
    uint8_t *crow_buf;
    uint8_t *last_row;
    unsigned int last_row_size;
    uint8_t *tmp_row;
    unsigned int tmp_row_size;
    uint8_t *buffer;
    int buffer_size;
    int pass;
    int crow_size; /* compressed row size (include filter type) */
    int row_size; /* decompressed row size */
    int pass_row_size; /* decompress row size of the current pass */
    int y;
    FFZStream zstream;
} PNGDecContext;
 
/* Mask to determine which pixels are valid in a pass */
static const uint8_t png_pass_mask[NB_PASSES] = {
    0x01, 0x01, 0x11, 0x11, 0x55, 0x55, 0xff,
};
 
/* Mask to determine which y pixels can be written in a pass */
static const uint8_t png_pass_dsp_ymask[NB_PASSES] = {
    0xff, 0xff, 0x0f, 0xff, 0x33, 0xff, 0x55,
};
 
/* Mask to determine which pixels to overwrite while displaying */
static const uint8_t png_pass_dsp_mask[NB_PASSES] = {
    0xff, 0x0f, 0xff, 0x33, 0xff, 0x55, 0xff
};
 
/* NOTE: we try to construct a good looking image at each pass. width
 * is the original image width. We also do pixel format conversion at
 * this stage */
static void png_put_interlaced_row(uint8_t *dst, int width,
                                   int bits_per_pixel, int pass,
                                   int color_type, const uint8_t *src)
{
    int x, mask, dsp_mask, j, src_x, b, bpp;
    uint8_t *d;
    const uint8_t *s;
 
    mask     = png_pass_mask[pass];
    dsp_mask = png_pass_dsp_mask[pass];
 
    switch (bits_per_pixel) {
    case 1:
        src_x = 0;
        for (x = 0; x < width; x++) {
            j = (x & 7);
            if ((dsp_mask << j) & 0x80) {
                b = (src[src_x >> 3] >> (7 - (src_x & 7))) & 1;
                dst[x >> 3] &= 0xFF7F>>j;
                dst[x >> 3] |= b << (7 - j);
            }
            if ((mask << j) & 0x80)
                src_x++;
        }
        break;
    case 2:
        src_x = 0;
        for (x = 0; x < width; x++) {
            int j2 = 2 * (x & 3);
            j = (x & 7);
            if ((dsp_mask << j) & 0x80) {
                b = (src[src_x >> 2] >> (6 - 2*(src_x & 3))) & 3;
                dst[x >> 2] &= 0xFF3F>>j2;
                dst[x >> 2] |= b << (6 - j2);
            }
            if ((mask << j) & 0x80)
                src_x++;
        }
        break;
    case 4:
        src_x = 0;
        for (x = 0; x < width; x++) {
            int j2 = 4*(x&1);
            j = (x & 7);
            if ((dsp_mask << j) & 0x80) {
                b = (src[src_x >> 1] >> (4 - 4*(src_x & 1))) & 15;
                dst[x >> 1] &= 0xFF0F>>j2;
                dst[x >> 1] |= b << (4 - j2);
            }
            if ((mask << j) & 0x80)
                src_x++;
        }
        break;
    default:
        bpp = bits_per_pixel >> 3;
        d   = dst;
        s   = src;
            for (x = 0; x < width; x++) {
                j = x & 7;
                if ((dsp_mask << j) & 0x80) {
                    memcpy(d, s, bpp);
                }
                d += bpp;
                if ((mask << j) & 0x80)
                    s += bpp;
            }
        break;
    }
}
 
void ff_add_png_paeth_prediction(uint8_t *dst, uint8_t *src, uint8_t *top,
                                 int w, int bpp)
{
    int i;
    for (i = 0; i < w; i++) {
        int a, b, c, p, pa, pb, pc;
 
        a = dst[i - bpp];
        b = top[i];
        c = top[i - bpp];
 
        p  = b - c;
        pc = a - c;
 
        pa = abs(p);
        pb = abs(pc);
        pc = abs(p + pc);
 
        if (pa <= pb && pa <= pc)
            p = a;
        else if (pb <= pc)
            p = b;
        else
            p = c;
        dst[i] = p + src[i];
    }
}
 
#define UNROLL1(bpp, op)                                                      \
    {                                                                         \
        r = dst[0];                                                           \
        if (bpp >= 2)                                                         \
            g = dst[1];                                                       \
        if (bpp >= 3)                                                         \
            b = dst[2];                                                       \
        if (bpp >= 4)                                                         \
            a = dst[3];                                                       \
        for (; i <= size - bpp; i += bpp) {                                   \
            dst[i + 0] = r = op(r, src[i + 0], last[i + 0]);                  \
            if (bpp == 1)                                                     \
                continue;                                                     \
            dst[i + 1] = g = op(g, src[i + 1], last[i + 1]);                  \
            if (bpp == 2)                                                     \
                continue;                                                     \
            dst[i + 2] = b = op(b, src[i + 2], last[i + 2]);                  \
            if (bpp == 3)                                                     \
                continue;                                                     \
            dst[i + 3] = a = op(a, src[i + 3], last[i + 3]);                  \
        }                                                                     \
    }
 
#define UNROLL_FILTER(op)                                                     \
    if (bpp == 1) {                                                           \
        UNROLL1(1, op)                                                        \
    } else if (bpp == 2) {                                                    \
        UNROLL1(2, op)                                                        \
    } else if (bpp == 3) {                                                    \
        UNROLL1(3, op)                                                        \
    } else if (bpp == 4) {                                                    \
        UNROLL1(4, op)                                                        \
    }                                                                         \
    for (; i < size; i++) {                                                   \
        dst[i] = op(dst[i - bpp], src[i], last[i]);                           \
    }
 
/* NOTE: 'dst' can be equal to 'last' */
void ff_png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
                       uint8_t *src, uint8_t *last, int size, int bpp)
{
    int i, p, r, g, b, a;
 
    switch (filter_type) {
    case PNG_FILTER_VALUE_NONE:
        memcpy(dst, src, size);
        break;
    case PNG_FILTER_VALUE_SUB:
        for (i = 0; i < bpp; i++)
            dst[i] = src[i];
        if (bpp == 4) {
            p = *(int *)dst;
            for (; i < size; i += bpp) {
                unsigned s = *(int *)(src + i);
                p = ((s & 0x7f7f7f7f) + (p & 0x7f7f7f7f)) ^ ((s ^ p) & 0x80808080);
                *(int *)(dst + i) = p;
            }
        } else {
#define OP_SUB(x, s, l) ((x) + (s))
            UNROLL_FILTER(OP_SUB);
        }
        break;
    case PNG_FILTER_VALUE_UP:
        dsp->add_bytes_l2(dst, src, last, size);
        break;
    case PNG_FILTER_VALUE_AVG:
        for (i = 0; i < bpp; i++) {
            p      = (last[i] >> 1);
            dst[i] = p + src[i];
        }
#define OP_AVG(x, s, l) (((((x) + (l)) >> 1) + (s)) & 0xff)
        UNROLL_FILTER(OP_AVG);
        break;
    case PNG_FILTER_VALUE_PAETH:
        for (i = 0; i < bpp; i++) {
            p      = last[i];
            dst[i] = p + src[i];
        }
        if (bpp > 2 && size > 4) {
            /* would write off the end of the array if we let it process
             * the last pixel with bpp=3 */
            int w = (bpp & 3) ? size - 3 : size;
 
            if (w > i) {
                dsp->add_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);
                i = w;
            }
        }
        ff_add_png_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);
        break;
    }
}
 
/* This used to be called "deloco" in FFmpeg
 * and is actually an inverse reversible colorspace transformation */
#define YUV2RGB(NAME, TYPE) \
static void deloco_ ## NAME(TYPE *dst, int size, int alpha) \
{ \
    int i; \
    for (i = 0; i < size - 2; i += 3 + alpha) { \
        int g = dst [i + 1]; \
        dst[i + 0] += g; \
        dst[i + 2] += g; \
    } \
}
 
YUV2RGB(rgb8, uint8_t)
YUV2RGB(rgb16, uint16_t)
 
static int percent_missing(PNGDecContext *s)
{
    if (s->interlace_type) {
        return 100 - 100 * s->pass / (NB_PASSES - 1);
    } else {
        return 100 - 100 * s->y / s->cur_h;
    }
}
 
/* process exactly one decompressed row */
static void png_handle_row(PNGDecContext *s, uint8_t *dst, ptrdiff_t dst_stride)
{
    uint8_t *ptr, *last_row;
    int got_line;
 
    if (!s->interlace_type) {
        ptr = dst + dst_stride * (s->y + s->y_offset) + s->x_offset * s->bpp;
        if (s->y == 0)
            last_row = s->last_row;
        else
            last_row = ptr - dst_stride;
 
        ff_png_filter_row(&s->dsp, ptr, s->crow_buf[0], s->crow_buf + 1,
                          last_row, s->row_size, s->bpp);
        /* loco lags by 1 row so that it doesn't interfere with top prediction */
        if (s->filter_type == PNG_FILTER_TYPE_LOCO && s->y > 0) {
            if (s->bit_depth == 16) {
                deloco_rgb16((uint16_t *)(ptr - dst_stride), s->row_size / 2,
                             s->color_type == PNG_COLOR_TYPE_RGB_ALPHA);
            } else {
                deloco_rgb8(ptr - dst_stride, s->row_size,
                            s->color_type == PNG_COLOR_TYPE_RGB_ALPHA);
            }
        }
        s->y++;
        if (s->y == s->cur_h) {
            s->pic_state |= PNG_ALLIMAGE;
            if (s->filter_type == PNG_FILTER_TYPE_LOCO) {
                if (s->bit_depth == 16) {
                    deloco_rgb16((uint16_t *)ptr, s->row_size / 2,
                                 s->color_type == PNG_COLOR_TYPE_RGB_ALPHA);
                } else {
                    deloco_rgb8(ptr, s->row_size,
                                s->color_type == PNG_COLOR_TYPE_RGB_ALPHA);
                }
            }
        }
    } else {
        got_line = 0;
        for (;;) {
            ptr = dst + dst_stride * (s->y + s->y_offset) + s->x_offset * s->bpp;
            if ((ff_png_pass_ymask[s->pass] << (s->y & 7)) & 0x80) {
                /* if we already read one row, it is time to stop to
                 * wait for the next one */
                if (got_line)
                    break;
                ff_png_filter_row(&s->dsp, s->tmp_row, s->crow_buf[0], s->crow_buf + 1,
                                  s->last_row, s->pass_row_size, s->bpp);
                FFSWAP(uint8_t *, s->last_row, s->tmp_row);
                FFSWAP(unsigned int, s->last_row_size, s->tmp_row_size);
                got_line = 1;
            }
            if ((png_pass_dsp_ymask[s->pass] << (s->y & 7)) & 0x80) {
                png_put_interlaced_row(ptr, s->cur_w, s->bits_per_pixel, s->pass,
                                       s->color_type, s->last_row);
            }
            s->y++;
            if (s->y == s->cur_h) {
                memset(s->last_row, 0, s->row_size);
                for (;;) {
                    if (s->pass == NB_PASSES - 1) {
                        s->pic_state |= PNG_ALLIMAGE;
                        goto the_end;
                    } else {
                        s->pass++;
                        s->y = 0;
                        s->pass_row_size = ff_png_pass_row_size(s->pass,
                                                                s->bits_per_pixel,
                                                                s->cur_w);
                        s->crow_size = s->pass_row_size + 1;
                        if (s->pass_row_size != 0)
                            break;
                        /* skip pass if empty row */
                    }
                }
            }
        }
the_end:;
    }
}
 
static int png_decode_idat(PNGDecContext *s, GetByteContext *gb,
                           uint8_t *dst, ptrdiff_t dst_stride)
{
    z_stream *const zstream = &s->zstream.zstream;
    int ret;
    zstream->avail_in = bytestream2_get_bytes_left(gb);
    zstream->next_in  = gb->buffer;
 
    /* decode one line if possible */
    while (zstream->avail_in > 0) {
        ret = inflate(zstream, Z_PARTIAL_FLUSH);
        if (ret != Z_OK && ret != Z_STREAM_END) {
            av_log(s->avctx, AV_LOG_ERROR, "inflate returned error %d\n", ret);
            return AVERROR_EXTERNAL;
        }
        if (zstream->avail_out == 0) {
            if (!(s->pic_state & PNG_ALLIMAGE)) {
                png_handle_row(s, dst, dst_stride);
            }
            zstream->avail_out = s->crow_size;
            zstream->next_out  = s->crow_buf;
        }
        if (ret == Z_STREAM_END && zstream->avail_in > 0) {
            av_log(s->avctx, AV_LOG_WARNING,
                   "%d undecompressed bytes left in buffer\n", zstream->avail_in);
            return 0;
        }
    }
    return 0;
}
 
static int decode_zbuf(AVBPrint *bp, const uint8_t *data,
                       const uint8_t *data_end, void *logctx)
{
    FFZStream z;
    z_stream *const zstream = &z.zstream;
    unsigned char *buf;
    unsigned buf_size;
    int ret = ff_inflate_init(&z, logctx);
    if (ret < 0)
        return ret;
 
    zstream->next_in  = data;
    zstream->avail_in = data_end - data;
    av_bprint_init(bp, 0, AV_BPRINT_SIZE_UNLIMITED);
 
    while (zstream->avail_in > 0) {
        av_bprint_get_buffer(bp, 2, &buf, &buf_size);
        if (buf_size < 2) {
            ret = AVERROR(ENOMEM);
            goto fail;
        }
        zstream->next_out  = buf;
        zstream->avail_out = buf_size - 1;
        ret = inflate(zstream, Z_PARTIAL_FLUSH);
        if (ret != Z_OK && ret != Z_STREAM_END) {
            ret = AVERROR_EXTERNAL;
            goto fail;
        }
        bp->len += zstream->next_out - buf;
        if (ret == Z_STREAM_END)
            break;
    }
    ff_inflate_end(&z);
    bp->str[bp->len] = 0;
    return 0;
 
fail:
    ff_inflate_end(&z);
    av_bprint_finalize(bp, NULL);
    return ret;
}
 
static char *iso88591_to_utf8(const char *in, size_t size_in)
{
    size_t extra = 0, i;
    char *out, *q;
 
    for (i = 0; i < size_in; i++)
        extra += !!(in[i] & 0x80);
    if (size_in == SIZE_MAX || extra > SIZE_MAX - size_in - 1)
        return NULL;
    q = out = av_malloc(size_in + extra + 1);
    if (!out)
        return NULL;
    for (i = 0; i < size_in; i++) {
        if (in[i] & 0x80) {
            *(q++) = 0xC0 | (in[i] >> 6);
            *(q++) = 0x80 | (in[i] & 0x3F);
        } else {
            *(q++) = in[i];
        }
    }
    *(q++) = 0;
    return out;
}
 
static int decode_text_chunk(PNGDecContext *s, GetByteContext *gb, int compressed)
{
    int ret, method;
    const uint8_t *data        = gb->buffer;
    const uint8_t *data_end    = gb->buffer_end;
    const char *keyword     = data;
    const char *keyword_end = memchr(keyword, 0, data_end - data);
    char *kw_utf8 = NULL, *txt_utf8 = NULL;
    const char *text;
    unsigned text_len;
    AVBPrint bp;
 
    if (!keyword_end)
        return AVERROR_INVALIDDATA;
    data = keyword_end + 1;
 
    if (compressed) {
        if (data == data_end)
            return AVERROR_INVALIDDATA;
        method = *(data++);
        if (method)
            return AVERROR_INVALIDDATA;
        if ((ret = decode_zbuf(&bp, data, data_end, s->avctx)) < 0)
            return ret;
        text     = bp.str;
        text_len = bp.len;
    } else {
        text     = data;
        text_len = data_end - data;
    }
 
    txt_utf8 = iso88591_to_utf8(text, text_len);
    if (compressed)
        av_bprint_finalize(&bp, NULL);
    if (!txt_utf8)
        return AVERROR(ENOMEM);
    kw_utf8  = iso88591_to_utf8(keyword, keyword_end - keyword);
    if (!kw_utf8) {
        av_free(txt_utf8);
        return AVERROR(ENOMEM);
    }
 
    av_dict_set(&s->frame_metadata, kw_utf8, txt_utf8,
                AV_DICT_DONT_STRDUP_KEY | AV_DICT_DONT_STRDUP_VAL);
    return 0;
}
 
static int decode_ihdr_chunk(AVCodecContext *avctx, PNGDecContext *s,
                             GetByteContext *gb)
{
    if (bytestream2_get_bytes_left(gb) != 13)
        return AVERROR_INVALIDDATA;
 
    if (s->pic_state & PNG_IDAT) {
        av_log(avctx, AV_LOG_ERROR, "IHDR after IDAT\n");
        return AVERROR_INVALIDDATA;
    }
 
    if (s->hdr_state & PNG_IHDR) {
        av_log(avctx, AV_LOG_ERROR, "Multiple IHDR\n");
        return AVERROR_INVALIDDATA;
    }
 
    s->width  = s->cur_w = bytestream2_get_be32(gb);
    s->height = s->cur_h = bytestream2_get_be32(gb);
    if (av_image_check_size(s->width, s->height, 0, avctx)) {
        s->cur_w = s->cur_h = s->width = s->height = 0;
        av_log(avctx, AV_LOG_ERROR, "Invalid image size\n");
        return AVERROR_INVALIDDATA;
    }
    s->bit_depth        = bytestream2_get_byte(gb);
    if (s->bit_depth != 1 && s->bit_depth != 2 && s->bit_depth != 4 &&
        s->bit_depth != 8 && s->bit_depth != 16) {
        av_log(avctx, AV_LOG_ERROR, "Invalid bit depth\n");
        goto error;
    }
    s->color_type       = bytestream2_get_byte(gb);
    s->compression_type = bytestream2_get_byte(gb);
    if (s->compression_type) {
        av_log(avctx, AV_LOG_ERROR, "Invalid compression method %d\n", s->compression_type);
        goto error;
    }
    s->filter_type      = bytestream2_get_byte(gb);
    s->interlace_type   = bytestream2_get_byte(gb);
    s->hdr_state |= PNG_IHDR;
    if (avctx->debug & FF_DEBUG_PICT_INFO)
        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);
 
    return 0;
error:
    s->cur_w = s->cur_h = s->width = s->height = 0;
    s->bit_depth = 8;
    return AVERROR_INVALIDDATA;
}
 
static int decode_phys_chunk(AVCodecContext *avctx, PNGDecContext *s,
                             GetByteContext *gb)
{
    if (s->pic_state & PNG_IDAT) {
        av_log(avctx, AV_LOG_ERROR, "pHYs after IDAT\n");
        return AVERROR_INVALIDDATA;
    }
    avctx->sample_aspect_ratio.num = bytestream2_get_be32(gb);
    avctx->sample_aspect_ratio.den = bytestream2_get_be32(gb);
    if (avctx->sample_aspect_ratio.num < 0 || avctx->sample_aspect_ratio.den < 0)
        avctx->sample_aspect_ratio = (AVRational){ 0, 1 };
    bytestream2_skip(gb, 1); /* unit specifier */
 
    return 0;
}
 
/*
 * This populates AVCodecContext fields so it must be called before
 * ff_thread_finish_setup() to avoid a race condition with respect to the
 * generic copying of avctx fields.
 */
static int populate_avctx_color_fields(AVCodecContext *avctx, AVFrame *frame)
{
    PNGDecContext *s = avctx->priv_data;
 
    if (s->have_cicp) {
        if (s->cicp_primaries >= AVCOL_PRI_NB)
            av_log(avctx, AV_LOG_WARNING, "unrecognized cICP primaries\n");
        else
            avctx->color_primaries = frame->color_primaries = s->cicp_primaries;
        if (s->cicp_trc >= AVCOL_TRC_NB)
            av_log(avctx, AV_LOG_WARNING, "unrecognized cICP transfer\n");
        else
            avctx->color_trc = frame->color_trc = s->cicp_trc;
        if (s->cicp_range == 0)
            av_log(avctx, AV_LOG_WARNING, "unsupported tv-range cICP chunk\n");
    } else if (s->iccp_data) {
        AVFrameSideData *sd = av_frame_new_side_data(frame, AV_FRAME_DATA_ICC_PROFILE, s->iccp_data_len);
        if (!sd)
            return AVERROR(ENOMEM);
        memcpy(sd->data, s->iccp_data, s->iccp_data_len);
        av_dict_set(&sd->metadata, "name", s->iccp_name, 0);
    } else if (s->have_srgb) {
        avctx->color_primaries = frame->color_primaries = AVCOL_PRI_BT709;
        avctx->color_trc = frame->color_trc = AVCOL_TRC_IEC61966_2_1;
    } else if (s->have_chrm) {
        AVColorPrimariesDesc desc;
        enum AVColorPrimaries prim;
        desc.wp.x = av_make_q(s->white_point[0], 100000);
        desc.wp.y = av_make_q(s->white_point[1], 100000);
        desc.prim.r.x = av_make_q(s->display_primaries[0][0], 100000);
        desc.prim.r.y = av_make_q(s->display_primaries[0][1], 100000);
        desc.prim.g.x = av_make_q(s->display_primaries[1][0], 100000);
        desc.prim.g.y = av_make_q(s->display_primaries[1][1], 100000);
        desc.prim.b.x = av_make_q(s->display_primaries[2][0], 100000);
        desc.prim.b.y = av_make_q(s->display_primaries[2][1], 100000);
        prim = av_csp_primaries_id_from_desc(&desc);
        if (prim != AVCOL_PRI_UNSPECIFIED)
            avctx->color_primaries = frame->color_primaries = prim;
        else
            av_log(avctx, AV_LOG_WARNING, "unknown cHRM primaries\n");
    }
 
    /* these chunks override gAMA */
    if (s->iccp_data || s->have_srgb || s->have_cicp) {
        av_dict_set(&s->frame_metadata, "gamma", NULL, 0);
    } else if (s->gamma) {
        /*
         * These values are 100000/2.2, 100000/2.8, 100000/2.6, and
         * 100000/1.0 respectively. 45455, 35714, and 38462, and 100000.
         * There's a 0.001 gamma tolerance here in case of floating
         * point issues when the PNG was written.
         *
         * None of the other enums have a pure gamma curve so it makes
         * sense to leave those to sRGB and cICP.
         */
        if (s->gamma > 45355 && s->gamma < 45555)
            avctx->color_trc = frame->color_trc = AVCOL_TRC_GAMMA22;
        else if (s->gamma > 35614 && s->gamma < 35814)
            avctx->color_trc = frame->color_trc = AVCOL_TRC_GAMMA28;
        else if (s->gamma > 38362 && s->gamma < 38562)
            avctx->color_trc = frame->color_trc = AVCOL_TRC_SMPTE428;
        else if (s->gamma > 99900 && s->gamma < 100100)
            avctx->color_trc = frame->color_trc = AVCOL_TRC_LINEAR;
    }
 
    /* we only support pc-range RGB */
    avctx->colorspace = frame->colorspace = AVCOL_SPC_RGB;
    avctx->color_range = frame->color_range = AVCOL_RANGE_JPEG;
 
    /*
     * tRNS sets alpha depth to full, so we ignore sBIT if set.
     * As a result we must wait until now to set
     * avctx->bits_per_raw_sample in case tRNS appears after sBIT
     */
    if (!s->has_trns && s->significant_bits > 0)
        avctx->bits_per_raw_sample = s->significant_bits;
 
    return 0;
}
 
static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
                             GetByteContext *gb, AVFrame *p)
{
    int ret;
    size_t byte_depth = s->bit_depth > 8 ? 2 : 1;
 
    if (!p)
        return AVERROR_INVALIDDATA;
    if (!(s->hdr_state & PNG_IHDR)) {
        av_log(avctx, AV_LOG_ERROR, "IDAT without IHDR\n");
        return AVERROR_INVALIDDATA;
    }
    if (!(s->pic_state & PNG_IDAT)) {
        /* init image info */
        ret = ff_set_dimensions(avctx, s->width, s->height);
        if (ret < 0)
            return ret;
 
        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       = (s->cur_w * s->bits_per_pixel + 7) >> 3;
 
        if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
                s->color_type == PNG_COLOR_TYPE_RGB) {
            avctx->pix_fmt = AV_PIX_FMT_RGB24;
        } else if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
                s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
            avctx->pix_fmt = AV_PIX_FMT_RGBA;
        } else if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
                s->color_type == PNG_COLOR_TYPE_GRAY) {
            avctx->pix_fmt = AV_PIX_FMT_GRAY8;
        } else if (s->bit_depth == 16 &&
                s->color_type == PNG_COLOR_TYPE_GRAY) {
            avctx->pix_fmt = AV_PIX_FMT_GRAY16BE;
        } else if (s->bit_depth == 16 &&
                s->color_type == PNG_COLOR_TYPE_RGB) {
            avctx->pix_fmt = AV_PIX_FMT_RGB48BE;
        } else if (s->bit_depth == 16 &&
                s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
            avctx->pix_fmt = AV_PIX_FMT_RGBA64BE;
        } else if ((s->bits_per_pixel == 1 || s->bits_per_pixel == 2 || s->bits_per_pixel == 4 || s->bits_per_pixel == 8) &&
                s->color_type == PNG_COLOR_TYPE_PALETTE) {
            avctx->pix_fmt = avctx->codec_id == AV_CODEC_ID_APNG ? AV_PIX_FMT_RGBA : AV_PIX_FMT_PAL8;
        } else if (s->bit_depth == 1 && s->bits_per_pixel == 1 && avctx->codec_id != AV_CODEC_ID_APNG) {
            avctx->pix_fmt = AV_PIX_FMT_MONOBLACK;
        } else if (s->bit_depth == 8 &&
                s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
            avctx->pix_fmt = AV_PIX_FMT_YA8;
        } else if (s->bit_depth == 16 &&
                s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
            avctx->pix_fmt = AV_PIX_FMT_YA16BE;
        } else {
            avpriv_report_missing_feature(avctx,
                                          "Bit depth %d color type %d",
                                          s->bit_depth, s->color_type);
            return AVERROR_PATCHWELCOME;
        }
 
        if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE) {
            switch (avctx->pix_fmt) {
            case AV_PIX_FMT_RGB24:
                avctx->pix_fmt = AV_PIX_FMT_RGBA;
                break;
 
            case AV_PIX_FMT_RGB48BE:
                avctx->pix_fmt = AV_PIX_FMT_RGBA64BE;
                break;
 
            case AV_PIX_FMT_GRAY8:
                avctx->pix_fmt = AV_PIX_FMT_YA8;
                break;
 
            case AV_PIX_FMT_GRAY16BE:
                avctx->pix_fmt = AV_PIX_FMT_YA16BE;
                break;
 
            default:
                avpriv_request_sample(avctx, "bit depth %d "
                        "and color type %d with TRNS",
                        s->bit_depth, s->color_type);
                return AVERROR_INVALIDDATA;
            }
 
            s->bpp += byte_depth;
        }
 
        ff_thread_release_ext_buffer(&s->picture);
        if (s->dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
            /* We only need a buffer for the current picture. */
            ret = ff_thread_get_buffer(avctx, p, 0);
            if (ret < 0)
                return ret;
        } else if (s->dispose_op == APNG_DISPOSE_OP_BACKGROUND) {
            /* We need a buffer for the current picture as well as
             * a buffer for the reference to retain. */
            ret = ff_thread_get_ext_buffer(avctx, &s->picture,
                                           AV_GET_BUFFER_FLAG_REF);
            if (ret < 0)
                return ret;
            ret = ff_thread_get_buffer(avctx, p, 0);
            if (ret < 0)
                return ret;
        } else {
            /* The picture output this time and the reference to retain coincide. */
            if ((ret = ff_thread_get_ext_buffer(avctx, &s->picture,
                                                AV_GET_BUFFER_FLAG_REF)) < 0)
                return ret;
            ret = av_frame_ref(p, s->picture.f);
            if (ret < 0)
                return ret;
        }
 
        p->pict_type        = AV_PICTURE_TYPE_I;
        p->flags           |= AV_FRAME_FLAG_KEY;
        p->flags |= AV_FRAME_FLAG_INTERLACED * !!s->interlace_type;
 
        if ((ret = populate_avctx_color_fields(avctx, p)) < 0)
            return ret;
        ff_thread_finish_setup(avctx);
 
        /* 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->cur_w);
            s->crow_size = s->pass_row_size + 1;
        }
        ff_dlog(avctx, "row_size=%d crow_size =%d\n",
                s->row_size, s->crow_size);
 
        /* copy the palette if needed */
        if (avctx->pix_fmt == AV_PIX_FMT_PAL8)
            memcpy(p->data[1], s->palette, 256 * sizeof(uint32_t));
        /* empty row is used if differencing to the first row */
        av_fast_padded_mallocz(&s->last_row, &s->last_row_size, s->row_size);
        if (!s->last_row)
            return AVERROR_INVALIDDATA;
        if (s->interlace_type ||
                s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
            av_fast_padded_malloc(&s->tmp_row, &s->tmp_row_size, s->row_size);
            if (!s->tmp_row)
                return AVERROR_INVALIDDATA;
        }
        /* compressed row */
        av_fast_padded_malloc(&s->buffer, &s->buffer_size, s->row_size + 16);
        if (!s->buffer)
            return AVERROR(ENOMEM);
 
        /* we want crow_buf+1 to be 16-byte aligned */
        s->crow_buf          = s->buffer + 15;
        s->zstream.zstream.avail_out = s->crow_size;
        s->zstream.zstream.next_out  = s->crow_buf;
    }
 
    s->pic_state |= PNG_IDAT;
 
    /* set image to non-transparent bpp while decompressing */
    if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE)
        s->bpp -= byte_depth;
 
    ret = png_decode_idat(s, gb, p->data[0], p->linesize[0]);
 
    if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE)
        s->bpp += byte_depth;
 
    if (ret < 0)
        return ret;
 
    return 0;
}
 
static int decode_plte_chunk(AVCodecContext *avctx, PNGDecContext *s,
                             GetByteContext *gb)
{
    int length = bytestream2_get_bytes_left(gb);
    int n, i, r, g, b;
 
    if ((length % 3) != 0 || length > 256 * 3)
        return AVERROR_INVALIDDATA;
    /* read the palette */
    n = length / 3;
    for (i = 0; i < n; i++) {
        r = bytestream2_get_byte(gb);
        g = bytestream2_get_byte(gb);
        b = bytestream2_get_byte(gb);
        s->palette[i] = (0xFFU << 24) | (r << 16) | (g << 8) | b;
    }
    for (; i < 256; i++)
        s->palette[i] = (0xFFU << 24);
    s->hdr_state |= PNG_PLTE;
 
    return 0;
}
 
static int decode_trns_chunk(AVCodecContext *avctx, PNGDecContext *s,
                             GetByteContext *gb)
{
    int length = bytestream2_get_bytes_left(gb);
    int v, i;
 
    if (!(s->hdr_state & PNG_IHDR)) {
        av_log(avctx, AV_LOG_ERROR, "trns before IHDR\n");
        return AVERROR_INVALIDDATA;
    }
 
    if (s->pic_state & PNG_IDAT) {
        av_log(avctx, AV_LOG_ERROR, "trns after IDAT\n");
        return AVERROR_INVALIDDATA;
    }
 
    if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
        if (length > 256 || !(s->hdr_state & PNG_PLTE))
            return AVERROR_INVALIDDATA;
 
        for (i = 0; i < length; i++) {
            unsigned v = bytestream2_get_byte(gb);
            s->palette[i] = (s->palette[i] & 0x00ffffff) | (v << 24);
        }
    } else if (s->color_type == PNG_COLOR_TYPE_GRAY || s->color_type == PNG_COLOR_TYPE_RGB) {
        if ((s->color_type == PNG_COLOR_TYPE_GRAY && length != 2) ||
            (s->color_type == PNG_COLOR_TYPE_RGB && length != 6) ||
            s->bit_depth == 1)
            return AVERROR_INVALIDDATA;
 
        for (i = 0; i < length / 2; i++) {
            /* only use the least significant bits */
            v = av_mod_uintp2(bytestream2_get_be16(gb), s->bit_depth);
 
            if (s->bit_depth > 8)
                AV_WB16(&s->transparent_color_be[2 * i], v);
            else
                s->transparent_color_be[i] = v;
        }
    } else {
        return AVERROR_INVALIDDATA;
    }
 
    s->has_trns = 1;
 
    return 0;
}
 
static int decode_iccp_chunk(PNGDecContext *s, GetByteContext *gb)
{
    int ret, cnt = 0;
    AVBPrint bp;
 
    while ((s->iccp_name[cnt++] = bytestream2_get_byte(gb)) && cnt < 81);
    if (cnt > 80) {
        av_log(s->avctx, AV_LOG_ERROR, "iCCP with invalid name!\n");
        ret = AVERROR_INVALIDDATA;
        goto fail;
    }
 
    if (bytestream2_get_byte(gb) != 0) {
        av_log(s->avctx, AV_LOG_ERROR, "iCCP with invalid compression!\n");
        ret =  AVERROR_INVALIDDATA;
        goto fail;
    }
 
    if ((ret = decode_zbuf(&bp, gb->buffer, gb->buffer_end, s->avctx)) < 0)
        return ret;
 
    av_freep(&s->iccp_data);
    ret = av_bprint_finalize(&bp, (char **)&s->iccp_data);
    if (ret < 0)
        return ret;
    s->iccp_data_len = bp.len;
 
    return 0;
fail:
    s->iccp_name[0] = 0;
    return ret;
}
 
static int decode_sbit_chunk(AVCodecContext *avctx, PNGDecContext *s,
                             GetByteContext *gb)
{
    int bits = 0;
    int channels;
 
    if (!(s->hdr_state & PNG_IHDR)) {
        av_log(avctx, AV_LOG_ERROR, "sBIT before IHDR\n");
        return AVERROR_INVALIDDATA;
    }
 
    if (s->pic_state & PNG_IDAT) {
        av_log(avctx, AV_LOG_ERROR, "sBIT after IDAT\n");
        return AVERROR_INVALIDDATA;
    }
 
    channels = ff_png_get_nb_channels(s->color_type);
 
    if (bytestream2_get_bytes_left(gb) != channels)
        return AVERROR_INVALIDDATA;
 
    for (int i = 0; i < channels; i++) {
        int b = bytestream2_get_byteu(gb);
        bits = FFMAX(b, bits);
    }
 
    if (bits < 0 || bits > s->bit_depth) {
        av_log(avctx, AV_LOG_ERROR, "Invalid significant bits: %d\n", bits);
        return AVERROR_INVALIDDATA;
    }
    s->significant_bits = bits;
 
    return 0;
}
 
static void handle_small_bpp(PNGDecContext *s, AVFrame *p)
{
    if (s->bits_per_pixel == 1 && s->color_type == PNG_COLOR_TYPE_PALETTE) {
        int i, j, k;
        uint8_t *pd = p->data[0];
        for (j = 0; j < s->height; j++) {
            i = s->width / 8;
            for (k = 7; k >= 1; k--)
                if ((s->width&7) >= k)
                    pd[8*i + k - 1] = (pd[i]>>8-k) & 1;
            for (i--; i >= 0; i--) {
                pd[8*i + 7]=  pd[i]     & 1;
                pd[8*i + 6]= (pd[i]>>1) & 1;
                pd[8*i + 5]= (pd[i]>>2) & 1;
                pd[8*i + 4]= (pd[i]>>3) & 1;
                pd[8*i + 3]= (pd[i]>>4) & 1;
                pd[8*i + 2]= (pd[i]>>5) & 1;
                pd[8*i + 1]= (pd[i]>>6) & 1;
                pd[8*i + 0]=  pd[i]>>7;
            }
            pd += p->linesize[0];
        }
    } else if (s->bits_per_pixel == 2) {
        int i, j;
        uint8_t *pd = p->data[0];
        for (j = 0; j < s->height; j++) {
            i = s->width / 4;
            if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
                if ((s->width&3) >= 3) pd[4*i + 2]= (pd[i] >> 2) & 3;
                if ((s->width&3) >= 2) pd[4*i + 1]= (pd[i] >> 4) & 3;
                if ((s->width&3) >= 1) pd[4*i + 0]=  pd[i] >> 6;
                for (i--; i >= 0; i--) {
                    pd[4*i + 3]=  pd[i]     & 3;
                    pd[4*i + 2]= (pd[i]>>2) & 3;
                    pd[4*i + 1]= (pd[i]>>4) & 3;
                    pd[4*i + 0]=  pd[i]>>6;
                }
            } else {
                if ((s->width&3) >= 3) pd[4*i + 2]= ((pd[i]>>2) & 3)*0x55;
                if ((s->width&3) >= 2) pd[4*i + 1]= ((pd[i]>>4) & 3)*0x55;
                if ((s->width&3) >= 1) pd[4*i + 0]= ( pd[i]>>6     )*0x55;
                for (i--; i >= 0; i--) {
                    pd[4*i + 3]= ( pd[i]     & 3)*0x55;
                    pd[4*i + 2]= ((pd[i]>>2) & 3)*0x55;
                    pd[4*i + 1]= ((pd[i]>>4) & 3)*0x55;
                    pd[4*i + 0]= ( pd[i]>>6     )*0x55;
                }
            }
            pd += p->linesize[0];
        }
    } else if (s->bits_per_pixel == 4) {
        int i, j;
        uint8_t *pd = p->data[0];
        for (j = 0; j < s->height; j++) {
            i = s->width/2;
            if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
                if (s->width&1) pd[2*i+0]= pd[i]>>4;
                for (i--; i >= 0; i--) {
                    pd[2*i + 1] = pd[i] & 15;
                    pd[2*i + 0] = pd[i] >> 4;
                }
            } else {
                if (s->width & 1) pd[2*i + 0]= (pd[i] >> 4) * 0x11;
                for (i--; i >= 0; i--) {
                    pd[2*i + 1] = (pd[i] & 15) * 0x11;
                    pd[2*i + 0] = (pd[i] >> 4) * 0x11;
                }
            }
            pd += p->linesize[0];
        }
    }
}
 
static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s,
                             GetByteContext *gb)
{
    uint32_t sequence_number;
    int cur_w, cur_h, x_offset, y_offset, dispose_op, blend_op;
 
    if (bytestream2_get_bytes_left(gb) != APNG_FCTL_CHUNK_SIZE)
        return AVERROR_INVALIDDATA;
 
    if (!(s->hdr_state & PNG_IHDR)) {
        av_log(avctx, AV_LOG_ERROR, "fctl before IHDR\n");
        return AVERROR_INVALIDDATA;
    }
 
    if (s->pic_state & PNG_IDAT) {
        av_log(avctx, AV_LOG_ERROR, "fctl after IDAT\n");
        return AVERROR_INVALIDDATA;
    }
 
    sequence_number = bytestream2_get_be32(gb);
    cur_w           = bytestream2_get_be32(gb);
    cur_h           = bytestream2_get_be32(gb);
    x_offset        = bytestream2_get_be32(gb);
    y_offset        = bytestream2_get_be32(gb);
    bytestream2_skip(gb, 4); /* delay_num (2), delay_den (2) */
    dispose_op      = bytestream2_get_byte(gb);
    blend_op        = bytestream2_get_byte(gb);
 
    if (sequence_number == 0 &&
        (cur_w != s->width ||
         cur_h != s->height ||
         x_offset != 0 ||
         y_offset != 0) ||
        cur_w <= 0 || cur_h <= 0 ||
        x_offset < 0 || y_offset < 0 ||
        cur_w > s->width - x_offset|| cur_h > s->height - y_offset)
            return AVERROR_INVALIDDATA;
 
    if (blend_op != APNG_BLEND_OP_OVER && blend_op != APNG_BLEND_OP_SOURCE) {
        av_log(avctx, AV_LOG_ERROR, "Invalid blend_op %d\n", blend_op);
        return AVERROR_INVALIDDATA;
    }
 
    if ((sequence_number == 0 || !s->last_picture.f->data[0]) &&
        dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
        // No previous frame to revert to for the first frame
        // Spec says to just treat it as a APNG_DISPOSE_OP_BACKGROUND
        dispose_op = APNG_DISPOSE_OP_BACKGROUND;
    }
 
    if (blend_op == APNG_BLEND_OP_OVER && !s->has_trns && (
            avctx->pix_fmt == AV_PIX_FMT_RGB24 ||
            avctx->pix_fmt == AV_PIX_FMT_RGB48BE ||
            avctx->pix_fmt == AV_PIX_FMT_GRAY8 ||
            avctx->pix_fmt == AV_PIX_FMT_GRAY16BE ||
            avctx->pix_fmt == AV_PIX_FMT_MONOBLACK
        )) {
        // APNG_BLEND_OP_OVER is the same as APNG_BLEND_OP_SOURCE when there is no alpha channel
        blend_op = APNG_BLEND_OP_SOURCE;
    }
 
    s->cur_w      = cur_w;
    s->cur_h      = cur_h;
    s->x_offset   = x_offset;
    s->y_offset   = y_offset;
    s->dispose_op = dispose_op;
    s->blend_op   = blend_op;
 
    return 0;
}
 
static void handle_p_frame_png(PNGDecContext *s, AVFrame *p)
{
    int i, j;
    uint8_t *pd      = p->data[0];
    uint8_t *pd_last = s->last_picture.f->data[0];
    int ls = av_image_get_linesize(p->format, s->width, 0);
 
    ls = FFMIN(ls, s->width * s->bpp);
 
    ff_thread_await_progress(&s->last_picture, INT_MAX, 0);
    for (j = 0; j < s->height; j++) {
        for (i = 0; i < ls; i++)
            pd[i] += pd_last[i];
        pd      += p->linesize[0];
        pd_last += s->last_picture.f->linesize[0];
    }
}
 
// divide by 255 and round to nearest
// apply a fast variant: (X+127)/255 = ((X+127)*257+257)>>16 = ((X+128)*257)>>16
#define FAST_DIV255(x) ((((x) + 128) * 257) >> 16)
 
static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
                               AVFrame *p)
{
    uint8_t       *dst        = p->data[0];
    ptrdiff_t      dst_stride = p->linesize[0];
    const uint8_t *src        = s->last_picture.f->data[0];
    ptrdiff_t      src_stride = s->last_picture.f->linesize[0];
    const int      bpp        = s->color_type == PNG_COLOR_TYPE_PALETTE ? 4 : s->bpp;
 
    size_t x, y;
 
    if (s->blend_op == APNG_BLEND_OP_OVER &&
        avctx->pix_fmt != AV_PIX_FMT_RGBA &&
        avctx->pix_fmt != AV_PIX_FMT_GRAY8A) {
        avpriv_request_sample(avctx, "Blending with pixel format %s",
                              av_get_pix_fmt_name(avctx->pix_fmt));
        return AVERROR_PATCHWELCOME;
    }
 
    ff_thread_await_progress(&s->last_picture, INT_MAX, 0);
 
    // copy unchanged rectangles from the last frame
    for (y = 0; y < s->y_offset; y++)
        memcpy(dst + y * dst_stride, src + y * src_stride, p->width * bpp);
    for (y = s->y_offset; y < s->y_offset + s->cur_h; y++) {
        memcpy(dst + y * dst_stride, src + y * src_stride, s->x_offset * bpp);
        memcpy(dst + y * dst_stride + (s->x_offset + s->cur_w) * bpp,
               src + y * src_stride + (s->x_offset + s->cur_w) * bpp,
               (p->width - s->cur_w - s->x_offset) * bpp);
    }
    for (y = s->y_offset + s->cur_h; y < p->height; y++)
        memcpy(dst + y * dst_stride, src + y * src_stride, p->width * bpp);
 
    if (s->blend_op == APNG_BLEND_OP_OVER) {
        // Perform blending
        for (y = s->y_offset; y < s->y_offset + s->cur_h; ++y) {
            uint8_t       *foreground = dst + dst_stride * y + bpp * s->x_offset;
            const uint8_t *background = src + src_stride * y + bpp * s->x_offset;
            for (x = s->x_offset; x < s->x_offset + s->cur_w; ++x, foreground += bpp, background += bpp) {
                size_t b;
                uint8_t foreground_alpha, background_alpha, output_alpha;
                uint8_t output[10];
 
                // Since we might be blending alpha onto alpha, we use the following equations:
                // output_alpha = foreground_alpha + (1 - foreground_alpha) * background_alpha
                // output = (foreground_alpha * foreground + (1 - foreground_alpha) * background_alpha * background) / output_alpha
 
                switch (avctx->pix_fmt) {
                case AV_PIX_FMT_RGBA:
                    foreground_alpha = foreground[3];
                    background_alpha = background[3];
                    break;
 
                case AV_PIX_FMT_GRAY8A:
                    foreground_alpha = foreground[1];
                    background_alpha = background[1];
                    break;
                }
 
                if (foreground_alpha == 255)
                    continue;
 
                if (foreground_alpha == 0) {
                    memcpy(foreground, background, bpp);
                    continue;
                }
 
                output_alpha = foreground_alpha + FAST_DIV255((255 - foreground_alpha) * background_alpha);
 
                av_assert0(bpp <= 10);
 
                for (b = 0; b < bpp - 1; ++b) {
                    if (output_alpha == 0) {
                        output[b] = 0;
                    } else if (background_alpha == 255) {
                        output[b] = FAST_DIV255(foreground_alpha * foreground[b] + (255 - foreground_alpha) * background[b]);
                    } else {
                        output[b] = (255 * foreground_alpha * foreground[b] + (255 - foreground_alpha) * background_alpha * background[b]) / (255 * output_alpha);
                    }
                }
                output[b] = output_alpha;
                memcpy(foreground, output, bpp);
            }
        }
    }
 
    return 0;
}
 
static void apng_reset_background(PNGDecContext *s, const AVFrame *p)
{
    // need to reset a rectangle to black
    av_unused int ret = av_frame_copy(s->picture.f, p);
    const int bpp = s->color_type == PNG_COLOR_TYPE_PALETTE ? 4 : s->bpp;
    const ptrdiff_t dst_stride = s->picture.f->linesize[0];
    uint8_t *dst = s->picture.f->data[0] + s->y_offset * dst_stride + bpp * s->x_offset;
 
    av_assert1(ret >= 0);
 
    for (size_t y = 0; y < s->cur_h; y++) {
        memset(dst, 0, bpp * s->cur_w);
        dst += dst_stride;
    }
}
 
static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
                               AVFrame *p, const AVPacket *avpkt)
{
    const AVCRC *crc_tab = av_crc_get_table(AV_CRC_32_IEEE_LE);
    uint32_t tag, length;
    int decode_next_dat = 0;
    int i, ret;
 
    for (;;) {
        GetByteContext gb_chunk;
 
        length = bytestream2_get_bytes_left(&s->gb);
        if (length <= 0) {
 
            if (avctx->codec_id == AV_CODEC_ID_PNG &&
                avctx->skip_frame == AVDISCARD_ALL) {
                return 0;
            }
 
            if (CONFIG_APNG_DECODER && avctx->codec_id == AV_CODEC_ID_APNG && length == 0) {
                if (!(s->pic_state & PNG_IDAT))
                    return 0;
                else
                    goto exit_loop;
            }
            av_log(avctx, AV_LOG_ERROR, "%d bytes left\n", length);
            if (   s->pic_state & PNG_ALLIMAGE
                && avctx->strict_std_compliance <= FF_COMPLIANCE_NORMAL)
                goto exit_loop;
            ret = AVERROR_INVALIDDATA;
            goto fail;
        }
 
        length = bytestream2_get_be32(&s->gb);
        if (length > 0x7fffffff || length + 8 > bytestream2_get_bytes_left(&s->gb)) {
            av_log(avctx, AV_LOG_ERROR, "chunk too big\n");
            ret = AVERROR_INVALIDDATA;
            goto fail;
        }
        if (avctx->err_recognition & (AV_EF_CRCCHECK | AV_EF_IGNORE_ERR)) {
            uint32_t crc_sig = AV_RB32(s->gb.buffer + length + 4);
            uint32_t crc_cal = ~av_crc(crc_tab, UINT32_MAX, s->gb.buffer, length + 4);
            if (crc_sig ^ crc_cal) {
                av_log(avctx, AV_LOG_ERROR, "CRC mismatch in chunk");
                if (avctx->err_recognition & AV_EF_EXPLODE) {
                    av_log(avctx, AV_LOG_ERROR, ", quitting\n");
                    ret = AVERROR_INVALIDDATA;
                    goto fail;
                }
                av_log(avctx, AV_LOG_ERROR, ", skipping\n");
                bytestream2_skip(&s->gb, length + 8); /* tag */
                continue;
            }
        }
        tag = bytestream2_get_le32(&s->gb);
        if (avctx->debug & FF_DEBUG_STARTCODE)
            av_log(avctx, AV_LOG_DEBUG, "png: tag=%s length=%u\n",
                   av_fourcc2str(tag), length);
 
        bytestream2_init(&gb_chunk, s->gb.buffer, length);
        bytestream2_skip(&s->gb, length + 4);
 
        if (avctx->codec_id == AV_CODEC_ID_PNG &&
            avctx->skip_frame == AVDISCARD_ALL) {
            switch(tag) {
            case MKTAG('I', 'H', 'D', 'R'):
            case MKTAG('p', 'H', 'Y', 's'):
            case MKTAG('t', 'E', 'X', 't'):
            case MKTAG('I', 'D', 'A', 'T'):
            case MKTAG('t', 'R', 'N', 'S'):
            case MKTAG('s', 'R', 'G', 'B'):
            case MKTAG('c', 'I', 'C', 'P'):
            case MKTAG('c', 'H', 'R', 'M'):
            case MKTAG('g', 'A', 'M', 'A'):
                break;
            default:
                continue;
            }
        }
 
        switch (tag) {
        case MKTAG('I', 'H', 'D', 'R'):
            if ((ret = decode_ihdr_chunk(avctx, s, &gb_chunk)) < 0)
                goto fail;
            break;
        case MKTAG('p', 'H', 'Y', 's'):
            if ((ret = decode_phys_chunk(avctx, s, &gb_chunk)) < 0)
                goto fail;
            break;
        case MKTAG('f', 'c', 'T', 'L'):
            if (!CONFIG_APNG_DECODER || avctx->codec_id != AV_CODEC_ID_APNG)
                continue;
            if ((ret = decode_fctl_chunk(avctx, s, &gb_chunk)) < 0)
                goto fail;
            decode_next_dat = 1;
            break;
        case MKTAG('f', 'd', 'A', 'T'):
            if (!CONFIG_APNG_DECODER || avctx->codec_id != AV_CODEC_ID_APNG)
                continue;
            if (!decode_next_dat || bytestream2_get_bytes_left(&gb_chunk) < 4) {
                ret = AVERROR_INVALIDDATA;
                goto fail;
            }
            bytestream2_get_be32(&gb_chunk);
            /* fallthrough */
        case MKTAG('I', 'D', 'A', 'T'):
            if (CONFIG_APNG_DECODER && avctx->codec_id == AV_CODEC_ID_APNG && !decode_next_dat)
                continue;
            if ((ret = decode_idat_chunk(avctx, s, &gb_chunk, p)) < 0)
                goto fail;
            break;
        case MKTAG('P', 'L', 'T', 'E'):
            decode_plte_chunk(avctx, s, &gb_chunk);
            break;
        case MKTAG('t', 'R', 'N', 'S'):
            decode_trns_chunk(avctx, s, &gb_chunk);
            break;
        case MKTAG('t', 'E', 'X', 't'):
            if (decode_text_chunk(s, &gb_chunk, 0) < 0)
                av_log(avctx, AV_LOG_WARNING, "Broken tEXt chunk\n");
            break;
        case MKTAG('z', 'T', 'X', 't'):
            if (decode_text_chunk(s, &gb_chunk, 1) < 0)
                av_log(avctx, AV_LOG_WARNING, "Broken zTXt chunk\n");
            break;
        case MKTAG('s', 'T', 'E', 'R'): {
            int mode = bytestream2_get_byte(&gb_chunk);
 
            if (mode == 0 || mode == 1) {
                s->stereo_mode = mode;
            } else {
                 av_log(avctx, AV_LOG_WARNING,
                        "Unknown value in sTER chunk (%d)\n", mode);
            }
            break;
        }
        case MKTAG('c', 'I', 'C', 'P'):
            s->cicp_primaries = bytestream2_get_byte(&gb_chunk);
            s->cicp_trc = bytestream2_get_byte(&gb_chunk);
            if (bytestream2_get_byte(&gb_chunk) != 0)
                av_log(avctx, AV_LOG_WARNING, "nonzero cICP matrix\n");
            s->cicp_range = bytestream2_get_byte(&gb_chunk);
            if (s->cicp_range != 0 && s->cicp_range != 1) {
                av_log(avctx, AV_LOG_ERROR, "invalid cICP range: %d\n", s->cicp_range);
                ret = AVERROR_INVALIDDATA;
                goto fail;
            }
            s->have_cicp = 1;
            break;
        case MKTAG('s', 'R', 'G', 'B'):
            /* skip rendering intent byte */
            bytestream2_skip(&gb_chunk, 1);
            s->have_srgb = 1;
            break;
        case MKTAG('i', 'C', 'C', 'P'): {
            if ((ret = decode_iccp_chunk(s, &gb_chunk)) < 0)
                goto fail;
            break;
        }
        case MKTAG('c', 'H', 'R', 'M'): {
            s->have_chrm = 1;
 
            s->white_point[0] = bytestream2_get_be32(&gb_chunk);
            s->white_point[1] = bytestream2_get_be32(&gb_chunk);
 
            /* RGB Primaries */
            for (i = 0; i < 3; i++) {
                s->display_primaries[i][0] = bytestream2_get_be32(&gb_chunk);
                s->display_primaries[i][1] = bytestream2_get_be32(&gb_chunk);
            }
 
            break;
        }
        case MKTAG('s', 'B', 'I', 'T'):
            if ((ret = decode_sbit_chunk(avctx, s, &gb_chunk)) < 0)
                goto fail;
            break;
        case MKTAG('g', 'A', 'M', 'A'): {
            AVBPrint bp;
            char *gamma_str;
            s->gamma = bytestream2_get_be32(&gb_chunk);
 
            av_bprint_init(&bp, 0, AV_BPRINT_SIZE_UNLIMITED);
            av_bprintf(&bp, "%i/%i", s->gamma, 100000);
            ret = av_bprint_finalize(&bp, &gamma_str);
            if (ret < 0)
                return ret;
 
            av_dict_set(&s->frame_metadata, "gamma", gamma_str, AV_DICT_DONT_STRDUP_VAL);
 
            break;
        }
        case MKTAG('I', 'E', 'N', 'D'):
            if (!(s->pic_state & PNG_ALLIMAGE))
                av_log(avctx, AV_LOG_ERROR, "IEND without all image\n");
            if (!(s->pic_state & (PNG_ALLIMAGE|PNG_IDAT))) {
                ret = AVERROR_INVALIDDATA;
                goto fail;
            }
            goto exit_loop;
        }
    }
exit_loop:
 
    if (!p)
        return AVERROR_INVALIDDATA;
 
    if (avctx->codec_id == AV_CODEC_ID_PNG &&
        avctx->skip_frame == AVDISCARD_ALL) {
        return 0;
    }
 
    if (percent_missing(s) > avctx->discard_damaged_percentage) {
        ret = AVERROR_INVALIDDATA;
        goto fail;
    }
 
    if (s->bits_per_pixel <= 4)
        handle_small_bpp(s, p);
 
    if (s->color_type == PNG_COLOR_TYPE_PALETTE && avctx->codec_id == AV_CODEC_ID_APNG) {
        for (int y = 0; y < s->height; y++) {
            uint8_t *row = &p->data[0][p->linesize[0] * y];
 
            for (int x = s->width - 1; x >= 0; x--) {
                const uint8_t idx = row[x];
 
                row[4*x+2] =  s->palette[idx]        & 0xFF;
                row[4*x+1] = (s->palette[idx] >> 8 ) & 0xFF;
                row[4*x+0] = (s->palette[idx] >> 16) & 0xFF;
                row[4*x+3] =  s->palette[idx] >> 24;
            }
        }
    }
 
    /* apply transparency if needed */
    if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE) {
        size_t byte_depth = s->bit_depth > 8 ? 2 : 1;
        size_t raw_bpp = s->bpp - byte_depth;
        ptrdiff_t x, y;
 
        av_assert0(s->bit_depth > 1);
 
        for (y = 0; y < s->height; ++y) {
            uint8_t *row = &p->data[0][p->linesize[0] * y];
 
            if (s->bpp == 2 && byte_depth == 1) {
                uint8_t *pixel = &row[2 * s->width - 1];
                uint8_t *rowp  = &row[1 * s->width - 1];
                int tcolor = s->transparent_color_be[0];
                for (x = s->width; x > 0; --x) {
                    *pixel-- = *rowp == tcolor ? 0 : 0xff;
                    *pixel-- = *rowp--;
                }
            } else if (s->bpp == 4 && byte_depth == 1) {
                uint8_t *pixel = &row[4 * s->width - 1];
                uint8_t *rowp  = &row[3 * s->width - 1];
                int tcolor = AV_RL24(s->transparent_color_be);
                for (x = s->width; x > 0; --x) {
                    *pixel-- = AV_RL24(rowp-2) == tcolor ? 0 : 0xff;
                    *pixel-- = *rowp--;
                    *pixel-- = *rowp--;
                    *pixel-- = *rowp--;
                }
            } else {
                /* since we're updating in-place, we have to go from right to left */
                for (x = s->width; x > 0; --x) {
                    uint8_t *pixel = &row[s->bpp * (x - 1)];
                    memmove(pixel, &row[raw_bpp * (x - 1)], raw_bpp);
 
                    if (!memcmp(pixel, s->transparent_color_be, raw_bpp)) {
                        memset(&pixel[raw_bpp], 0, byte_depth);
                    } else {
                        memset(&pixel[raw_bpp], 0xff, byte_depth);
                    }
                }
            }
        }
    }
 
    /* handle P-frames only if a predecessor frame is available */
    if (s->last_picture.f->data[0]) {
        if (   !(avpkt->flags & AV_PKT_FLAG_KEY) && avctx->codec_tag != AV_RL32("MPNG")
            && s->last_picture.f->width == p->width
            && s->last_picture.f->height== p->height
            && s->last_picture.f->format== p->format
         ) {
            if (CONFIG_PNG_DECODER && avctx->codec_id != AV_CODEC_ID_APNG)
                handle_p_frame_png(s, p);
            else if (CONFIG_APNG_DECODER &&
                     avctx->codec_id == AV_CODEC_ID_APNG &&
                     (ret = handle_p_frame_apng(avctx, s, p)) < 0)
                goto fail;
        }
    }
    if (CONFIG_APNG_DECODER && s->dispose_op == APNG_DISPOSE_OP_BACKGROUND)
        apng_reset_background(s, p);
 
    ff_thread_report_progress(&s->picture, INT_MAX, 0);
 
    return 0;
 
fail:
    ff_thread_report_progress(&s->picture, INT_MAX, 0);
    return ret;
}
 
static void clear_frame_metadata(PNGDecContext *s)
{
    av_freep(&s->iccp_data);
    s->iccp_data_len = 0;
    s->iccp_name[0]  = 0;
 
    s->stereo_mode = -1;
 
    s->have_chrm = 0;
    s->have_srgb = 0;
    s->have_cicp = 0;
 
    av_dict_free(&s->frame_metadata);
}
 
static int output_frame(PNGDecContext *s, AVFrame *f)
{
    int ret;
 
    if (s->stereo_mode >= 0) {
        AVStereo3D *stereo3d = av_stereo3d_create_side_data(f);
        if (!stereo3d) {
            ret = AVERROR(ENOMEM);
            goto fail;
        }
 
        stereo3d->type  = AV_STEREO3D_SIDEBYSIDE;
        stereo3d->flags = s->stereo_mode ? 0 : AV_STEREO3D_FLAG_INVERT;
    }
 
    FFSWAP(AVDictionary*, f->metadata, s->frame_metadata);
 
    return 0;
fail:
    av_frame_unref(f);
    return ret;
}
 
#if CONFIG_PNG_DECODER
static int decode_frame_png(AVCodecContext *avctx, AVFrame *p,
                            int *got_frame, AVPacket *avpkt)
{
    PNGDecContext *const s = avctx->priv_data;
    const uint8_t *buf     = avpkt->data;
    int buf_size           = avpkt->size;
    int64_t sig;
    int ret;
 
    clear_frame_metadata(s);
 
    bytestream2_init(&s->gb, buf, buf_size);
 
    /* check signature */
    sig = bytestream2_get_be64(&s->gb);
    if (sig != PNGSIG &&
        sig != MNGSIG) {
        av_log(avctx, AV_LOG_ERROR, "Invalid PNG signature 0x%08"PRIX64".\n", sig);
        return AVERROR_INVALIDDATA;
    }
 
    s->y = s->has_trns = 0;
    s->hdr_state = 0;
    s->pic_state = 0;
 
    /* Reset z_stream */
    ret = inflateReset(&s->zstream.zstream);
    if (ret != Z_OK)
        return AVERROR_EXTERNAL;
 
    if ((ret = decode_frame_common(avctx, s, p, avpkt)) < 0)
        goto the_end;
 
    if (avctx->skip_frame == AVDISCARD_ALL) {
        *got_frame = 0;
        ret = bytestream2_tell(&s->gb);
        goto the_end;
    }
 
    ret = output_frame(s, p);
    if (ret < 0)
        goto the_end;
 
    if (!(avctx->active_thread_type & FF_THREAD_FRAME)) {
        ff_thread_release_ext_buffer(&s->last_picture);
        FFSWAP(ThreadFrame, s->picture, s->last_picture);
    }
 
    *got_frame = 1;
 
    ret = bytestream2_tell(&s->gb);
the_end:
    s->crow_buf = NULL;
    return ret;
}
#endif
 
#if CONFIG_APNG_DECODER
static int decode_frame_apng(AVCodecContext *avctx, AVFrame *p,
                             int *got_frame, AVPacket *avpkt)
{
    PNGDecContext *const s = avctx->priv_data;
    int ret;
 
    clear_frame_metadata(s);
 
    if (!(s->hdr_state & PNG_IHDR)) {
        if (!avctx->extradata_size)
            return AVERROR_INVALIDDATA;
 
        if ((ret = inflateReset(&s->zstream.zstream)) != Z_OK)
            return AVERROR_EXTERNAL;
        bytestream2_init(&s->gb, avctx->extradata, avctx->extradata_size);
        if ((ret = decode_frame_common(avctx, s, NULL, avpkt)) < 0)
            return ret;
    }
 
    /* reset state for a new frame */
    if ((ret = inflateReset(&s->zstream.zstream)) != Z_OK)
        return AVERROR_EXTERNAL;
    s->y = 0;
    s->pic_state = 0;
    bytestream2_init(&s->gb, avpkt->data, avpkt->size);
    if ((ret = decode_frame_common(avctx, s, p, avpkt)) < 0)
        return ret;
 
    if (!(s->pic_state & PNG_ALLIMAGE))
        av_log(avctx, AV_LOG_WARNING, "Frame did not contain a complete image\n");
    if (!(s->pic_state & (PNG_ALLIMAGE|PNG_IDAT)))
        return AVERROR_INVALIDDATA;
 
    ret = output_frame(s, p);
    if (ret < 0)
        return ret;
 
    if (!(avctx->active_thread_type & FF_THREAD_FRAME)) {
        if (s->dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
            ff_thread_release_ext_buffer(&s->picture);
        } else {
            ff_thread_release_ext_buffer(&s->last_picture);
            FFSWAP(ThreadFrame, s->picture, s->last_picture);
        }
    }
 
    *got_frame = 1;
    return bytestream2_tell(&s->gb);
}
#endif
 
#if HAVE_THREADS
static int update_thread_context(AVCodecContext *dst, const AVCodecContext *src)
{
    PNGDecContext *psrc = src->priv_data;
    PNGDecContext *pdst = dst->priv_data;
    ThreadFrame *src_frame = NULL;
    int ret;
 
    if (dst == src)
        return 0;
 
    if (CONFIG_APNG_DECODER && dst->codec_id == AV_CODEC_ID_APNG) {
 
        pdst->width             = psrc->width;
        pdst->height            = psrc->height;
        pdst->bit_depth         = psrc->bit_depth;
        pdst->color_type        = psrc->color_type;
        pdst->compression_type  = psrc->compression_type;
        pdst->interlace_type    = psrc->interlace_type;
        pdst->filter_type       = psrc->filter_type;
        pdst->has_trns = psrc->has_trns;
        memcpy(pdst->transparent_color_be, psrc->transparent_color_be, sizeof(pdst->transparent_color_be));
 
        memcpy(pdst->palette, psrc->palette, sizeof(pdst->palette));
 
        pdst->hdr_state |= psrc->hdr_state;
    }
 
    src_frame = psrc->dispose_op == APNG_DISPOSE_OP_PREVIOUS ?
                &psrc->last_picture : &psrc->picture;
 
    ff_thread_release_ext_buffer(&pdst->last_picture);
    if (src_frame && src_frame->f->data[0]) {
        ret = ff_thread_ref_frame(&pdst->last_picture, src_frame);
        if (ret < 0)
            return ret;
    }
 
    return 0;
}
#endif
 
static av_cold int png_dec_init(AVCodecContext *avctx)
{
    PNGDecContext *s = avctx->priv_data;
 
    avctx->color_range = AVCOL_RANGE_JPEG;
 
    s->avctx = avctx;
    s->last_picture.f = av_frame_alloc();
    s->picture.f = av_frame_alloc();
    if (!s->last_picture.f || !s->picture.f)
        return AVERROR(ENOMEM);
 
    ff_pngdsp_init(&s->dsp);
 
    return ff_inflate_init(&s->zstream, avctx);
}
 
static av_cold int png_dec_end(AVCodecContext *avctx)
{
    PNGDecContext *s = avctx->priv_data;
 
    ff_thread_release_ext_buffer(&s->last_picture);
    av_frame_free(&s->last_picture.f);
    ff_thread_release_ext_buffer(&s->picture);
    av_frame_free(&s->picture.f);
    av_freep(&s->buffer);
    s->buffer_size = 0;
    av_freep(&s->last_row);
    s->last_row_size = 0;
    av_freep(&s->tmp_row);
    s->tmp_row_size = 0;
 
    av_freep(&s->iccp_data);
    av_dict_free(&s->frame_metadata);
    ff_inflate_end(&s->zstream);
 
    return 0;
}
 
#if CONFIG_APNG_DECODER
const FFCodec ff_apng_decoder = {
    .p.name         = "apng",
    CODEC_LONG_NAME("APNG (Animated Portable Network Graphics) image"),
    .p.type         = AVMEDIA_TYPE_VIDEO,
    .p.id           = AV_CODEC_ID_APNG,
    .priv_data_size = sizeof(PNGDecContext),
    .init           = png_dec_init,
    .close          = png_dec_end,
    FF_CODEC_DECODE_CB(decode_frame_apng),
    UPDATE_THREAD_CONTEXT(update_thread_context),
    .p.capabilities = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS,
    .caps_internal  = FF_CODEC_CAP_INIT_CLEANUP |
                      FF_CODEC_CAP_ALLOCATE_PROGRESS |
                      FF_CODEC_CAP_ICC_PROFILES,
};
#endif
 
#if CONFIG_PNG_DECODER
const FFCodec ff_png_decoder = {
    .p.name         = "png",
    CODEC_LONG_NAME("PNG (Portable Network Graphics) image"),
    .p.type         = AVMEDIA_TYPE_VIDEO,
    .p.id           = AV_CODEC_ID_PNG,
    .priv_data_size = sizeof(PNGDecContext),
    .init           = png_dec_init,
    .close          = png_dec_end,
    FF_CODEC_DECODE_CB(decode_frame_png),
    UPDATE_THREAD_CONTEXT(update_thread_context),
    .p.capabilities = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS,
    .caps_internal  = FF_CODEC_CAP_SKIP_FRAME_FILL_PARAM |
                      FF_CODEC_CAP_ALLOCATE_PROGRESS | FF_CODEC_CAP_INIT_CLEANUP |
                      FF_CODEC_CAP_ICC_PROFILES,
};
#endif