png.c

ffmpeg源码分析

/*
 * PNG image format
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
#include "avcodec.h"

/* TODO:
 * - add 2, 4 and 16 bit depth support
 * - use filters when generating a png (better compression)
 */

#ifdef CONFIG_ZLIB
#include <zlib.h>

//#define DEBUG

#define PNG_COLOR_MASK_PALETTE    1
#define PNG_COLOR_MASK_COLOR      2
#define PNG_COLOR_MASK_ALPHA      4

#define PNG_COLOR_TYPE_GRAY 0
#define PNG_COLOR_TYPE_PALETTE  (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)
#define PNG_COLOR_TYPE_RGB        (PNG_COLOR_MASK_COLOR)
#define PNG_COLOR_TYPE_RGB_ALPHA  (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_ALPHA)
#define PNG_COLOR_TYPE_GRAY_ALPHA (PNG_COLOR_MASK_ALPHA)

#define PNG_FILTER_VALUE_NONE  0
#define PNG_FILTER_VALUE_SUB   1
#define PNG_FILTER_VALUE_UP    2
#define PNG_FILTER_VALUE_AVG   3
#define PNG_FILTER_VALUE_PAETH 4

#define PNG_IHDR      0x0001
#define PNG_IDAT      0x0002
#define PNG_ALLIMAGE  0x0004
#define PNG_PLTE      0x0008

#define NB_PASSES 7

#define IOBUF_SIZE 4096

typedef struct PNGContext {
    uint8_t *bytestream;
    uint8_t *bytestream_start;
    uint8_t *bytestream_end;
    AVFrame picture;

    int state;
    int width, height;
    int bit_depth;
    int color_type;
    int compression_type;
    int interlace_type;
    int filter_type;
    int channels;
    int bits_per_pixel;
    int bpp;

    uint8_t *image_buf;
    int image_linesize;
    uint32_t palette[256];
    uint8_t *crow_buf;
    uint8_t *last_row;
    uint8_t *tmp_row;
    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;
    z_stream zstream;
    uint8_t buf[IOBUF_SIZE];
} PNGContext;

static unsigned int get32(uint8_t **b){
    (*b) += 4;
    return ((*b)[-4]<<24) + ((*b)[-3]<<16) + ((*b)[-2]<<8) + (*b)[-1];
}

static void put32(uint8_t **b, unsigned int v){
    *(*b)++= v>>24;
    *(*b)++= v>>16;
    *(*b)++= v>>8;
    *(*b)++= v;
}

static const uint8_t pngsig[8] = {137, 80, 78, 71, 13, 10, 26, 10};

/* Mask to determine which y pixels are valid in a pass */
static const uint8_t png_pass_ymask[NB_PASSES] = {
    0x80, 0x80, 0x08, 0x88, 0x22, 0xaa, 0x55,
};

/* 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, 0xcc, 0x33, 0xff, 0x55,
};

/* minimum x value */
static const uint8_t png_pass_xmin[NB_PASSES] = {
    0, 4, 0, 2, 0, 1, 0
};

/* x shift to get row width */
static const uint8_t png_pass_xshift[NB_PASSES] = {
    3, 3, 2, 2, 1, 1, 0
};

/* Mask to determine which pixels are valid in a pass */
static const uint8_t png_pass_mask[NB_PASSES] = {
    0x80, 0x08, 0x88, 0x22, 0xaa, 0x55, 0xff
};

/* 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
};
#if 0
static int png_probe(AVProbeData *pd)
{
    if (pd->buf_size >= 8 &&
        memcmp(pd->buf, pngsig, 8) == 0)
        return AVPROBE_SCORE_MAX;
    else
        return 0;
}
#endif
static void *png_zalloc(void *opaque, unsigned int items, unsigned int size)
{
    if(items >= UINT_MAX / size)
        return NULL;
    return av_malloc(items * size);
}

static void png_zfree(void *opaque, void *ptr)
{
    av_free(ptr);
}

static int png_get_nb_channels(int color_type)
{
    int channels;
    channels = 1;
    if ((color_type & (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)) ==
        PNG_COLOR_MASK_COLOR)
        channels = 3;
    if (color_type & PNG_COLOR_MASK_ALPHA)
        channels++;
    return channels;
}

/* compute the row size of an interleaved pass */
static int png_pass_row_size(int pass, int bits_per_pixel, int width)
{
    int shift, xmin, pass_width;

    xmin = png_pass_xmin[pass];
    if (width <= xmin)
        return 0;
    shift = png_pass_xshift[pass];
    pass_width = (width - xmin + (1 << shift) - 1) >> shift;
    return (pass_width * bits_per_pixel + 7) >> 3;
}

/* NOTE: we try to construct a good looking image at each pass. width
   is the original image width. We also do pixel format convertion 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:
        /* we must intialize the line to zero before writing to it */
        if (pass == 0)
            memset(dst, 0, (width + 7) >> 3);
        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] |= b << (7 - j);
            }
            if ((mask << j) & 0x80)
                src_x++;
        }
        break;
    default:
        bpp = bits_per_pixel >> 3;
        d = dst;
        s = src;
        if (color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
            for(x = 0; x < width; x++) {
                j = x & 7;
                if ((dsp_mask << j) & 0x80) {
                    *(uint32_t *)d = (s[3] << 24) | (s[0] << 16) | (s[1] << 8) | s[2];
                }
                d += bpp;
                if ((mask << j) & 0x80)
                    s += bpp;
            }
        } else {
            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;
    }
}

static void png_get_interlaced_row(uint8_t *dst, int row_size,
                                   int bits_per_pixel, int pass,
                                   const uint8_t *src, int width)
{
    int x, mask, dst_x, j, b, bpp;
    uint8_t *d;
    const uint8_t *s;

    mask = png_pass_mask[pass];
    switch(bits_per_pixel) {
    case 1:
        memset(dst, 0, row_size);
        dst_x = 0;
        for(x = 0; x < width; x++) {
            j = (x & 7);
            if ((mask << j) & 0x80) {
                b = (src[x >> 3] >> (7 - j)) & 1;
                dst[dst_x >> 3] |= b << (7 - (dst_x & 7));
                dst_x++;
            }
        }
        break;
    default:
        bpp = bits_per_pixel >> 3;
        d = dst;
        s = src;
        for(x = 0; x < width; x++) {
            j = x & 7;
            if ((mask << j) & 0x80) {
                memcpy(d, s, bpp);
                d += bpp;
            }
            s += bpp;
        }
        break;
    }
}

/* XXX: optimize */
/* NOTE: 'dst' can be equal to 'last' */
static void png_filter_row(uint8_t *dst, int filter_type,
                           uint8_t *src, uint8_t *last, int size, int bpp)
{
    int i, p;

    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];
        }
        for(i = bpp; i < size; i++) {
            p = dst[i - bpp];
            dst[i] = p + src[i];
        }
        break;
    case PNG_FILTER_VALUE_UP:
        for(i = 0; i < size; i++) {
            p = last[i];
            dst[i] = p + src[i];
        }
        break;
    case PNG_FILTER_VALUE_AVG:
        for(i = 0; i < bpp; i++) {
            p = (last[i] >> 1);
            dst[i] = p + src[i];
        }
        for(i = bpp; i < size; i++) {
            p = ((dst[i - bpp] + last[i]) >> 1);
            dst[i] = p + src[i];
        }
        break;
    case PNG_FILTER_VALUE_PAETH:
        for(i = 0; i < bpp; i++) {
            p = last[i];
            dst[i] = p + src[i];
        }
        for(i = bpp; i < size; i++) {
            int a, b, c, pa, pb, pc;

            a = dst[i - bpp];
            b = last[i];
            c = last[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];
        }
        break;
    }
}

static void convert_from_rgba32(uint8_t *dst, const uint8_t *src, int width)
{
    uint8_t *d;
    int j;
    unsigned int v;

    d = dst;
    for(j = 0; j < width; j++) {
        v = ((uint32_t *)src)[j];
        d[0] = v >> 16;
        d[1] = v >> 8;
        d[2] = v;
        d[3] = v >> 24;
        d += 4;
    }
}

static void convert_to_rgba32(uint8_t *dst, const uint8_t *src, int width)
{
    int j;
    unsigned int r, g, b, a;

    for(j = 0;j < width; j++) {
        r = src[0];
        g = src[1];
        b = src[2];
        a = src[3];
        *(uint32_t *)dst = (a << 24) | (r << 16) | (g << 8) | b;
        dst += 4;
        src += 4;
    }
}

/* process exactly one decompressed row */
static void png_handle_row(PNGContext *s)
{
    uint8_t *ptr, *last_row;
    int got_line;

    if (!s->interlace_type) {
        ptr = s->image_buf + s->image_linesize * s->y;
        /* need to swap bytes correctly for RGB_ALPHA */
        if (s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
            png_filter_row(s->tmp_row, s->crow_buf[0], s->crow_buf + 1,
                           s->last_row, s->row_size, s->bpp);
            memcpy(s->last_row, s->tmp_row, s->row_size);
            convert_to_rgba32(ptr, s->tmp_row, s->width);
        } else {
            /* in normal case, we avoid one copy */
            if (s->y == 0)
                last_row = s->last_row;
            else
                last_row = ptr - s->image_linesize;

            png_filter_row(ptr, s->crow_buf[0], s->crow_buf + 1,
                           last_row, s->row_size, s->bpp);
        }
        s->y++;
        if (s->y == s->height) {
            s->state |= PNG_ALLIMAGE;
        }
    } else {
        got_line = 0;
        for(;;) {
            ptr = s->image_buf + s->image_linesize * s->y;
            if ((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;
                png_filter_row(s->tmp_row, s->crow_buf[0], s->crow_buf + 1,
                               s->last_row, s->pass_row_size, s->bpp);
                memcpy(s->last_row, s->tmp_row, s->pass_row_size);
                got_line = 1;
            }
            if ((png_pass_dsp_ymask[s->pass] << (s->y & 7)) & 0x80) {
                /* NOTE: rgba32 is handled directly in png_put_interlaced_row */
                png_put_interlaced_row(ptr, s->width, s->bits_per_pixel, s->pass,
                                       s->color_type, s->last_row);
            }
            s->y++;
            if (s->y == s->height) {
                for(;;) {
                    if (s->pass == NB_PASSES - 1) {
                        s->state |= PNG_ALLIMAGE;
                        goto the_end;
                    } else {
                        s->pass++;
                        s->y = 0;
                        s->pass_row_size = png_pass_row_size(s->pass,
                                                             s->bits_per_pixel,
                                                             s->width);
                        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(PNGContext *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)
{