dec_png.c

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <png.h>
#include "grib2_int.h"
 
struct png_stream
{
    unsigned char *stream_ptr; 
    g2int stream_len; 
};
typedef struct png_stream png_stream; 
void user_read_data(png_structp, png_bytep, png_uint_32);
 
void
user_read_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
{
    char *ptr;
    g2int offset;
    png_stream *mem;
 
    mem = (png_stream *)png_get_io_ptr(png_ptr);
    ptr = (void *)mem->stream_ptr;
    offset = mem->stream_len;
    memcpy(data, ptr + offset, length);
    mem->stream_len += length;
}
 
int
dec_png(unsigned char *pngbuf, g2int *width, g2int *height,
        unsigned char *cout)
{
    int interlace, color, compres, filter, bit_depth;
    g2int j, k, n, bytes, clen;
    png_structp png_ptr;
    png_infop info_ptr, end_info;
    png_bytepp row_pointers;
    png_stream read_io_ptr;
    png_uint_32 h32, w32;
 
    /* Check if stream is a valid PNG format. */
    if (png_sig_cmp(pngbuf, 0, 8) != 0)
        return -3;
 
    /* Create and initialize png_structs. */
    if (!(png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, (png_voidp)NULL,
                                           NULL, NULL)))
        return -1;
 
    if (!(info_ptr = png_create_info_struct(png_ptr)))
    {
        png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
        return -2;
    }
 
    if (!(end_info = png_create_info_struct(png_ptr)))
    {
        png_destroy_read_struct(&png_ptr, (png_infopp)info_ptr, (png_infopp)NULL);
        return -2;
    }
 
    /* Set Error callback. */
    if (setjmp(png_jmpbuf(png_ptr)))
    {
        png_destroy_read_struct(&png_ptr,  &info_ptr, &end_info);
        return -3;
    }
 
    /* Initialize info for reading PNG stream from memory. */
    read_io_ptr.stream_ptr = (png_voidp)pngbuf;
    read_io_ptr.stream_len = 0;
 
    /* Set new custom read function. */
    png_set_read_fn(png_ptr, (png_voidp)&read_io_ptr, (png_rw_ptr)user_read_data);
 
    /* Read and decode PNG stream. */
    png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
 
    /* Get pointer to each row of image data. */
    row_pointers = png_get_rows(png_ptr, info_ptr);
 
    /* Get image info, such as size, depth, colortype, etc... */
    /*printf("SAGT:png %d %d %d\n", info_ptr->width, info_ptr->height, info_ptr->bit_depth);*/
    // (void)png_get_IHDR(png_ptr,  info_ptr,  (png_uint_32 *)width,  (png_uint_32 *)height,
    (void)png_get_IHDR(png_ptr, info_ptr, &w32, &h32,
                       &bit_depth, &color, &interlace, &compres, &filter);
 
    *height = h32;
    *width = w32;
 
    /* Check if image was grayscale. */
    /*
      if (color != PNG_COLOR_TYPE_GRAY) {
      fprintf(stderr, "dec_png: Grayscale image was expected. \n");
      }
    */
    if (color == PNG_COLOR_TYPE_RGB)
        bit_depth = 24;
    else if (color == PNG_COLOR_TYPE_RGB_ALPHA)
        bit_depth = 32;
 
    /* Copy image data to output string   */
    n = 0;
    bytes = bit_depth / 8;
    clen = (*width) * bytes;
    for (j = 0; j < *height; j++)
    {
        for (k = 0; k < clen; k++)
        {
            cout[n] = *(row_pointers[j] + k);
            n++;
        }
    }
 
    /* Clean up. */
    png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
    return 0;
}