enc_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_write_data(png_structp, png_bytep, png_uint_32);
void user_flush_data(png_structp);
 
void
user_write_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
{
    unsigned char *ptr;
    g2int offset;
    png_stream *mem;
 
    mem = (png_stream *)png_get_io_ptr(png_ptr);
    ptr = mem->stream_ptr;
    offset = mem->stream_len;
    memcpy(ptr + offset, data, length);
    mem->stream_len += length;
}
 
void user_flush_data(png_structp png_ptr)
{
}
 
int
enc_png(unsigned char *data, g2int width, g2int height, g2int nbits,
        unsigned char *pngbuf)
{
    int color_type;
    g2int j, bytes, pnglen, bit_depth;
    png_structp png_ptr;
    png_infop info_ptr;
    png_bytep **row_pointers;
    png_stream write_io_ptr;
 
    /* Create and initialize png_structs. */
    if (!(png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL)))
        return -1;
 
    if (!(info_ptr = png_create_info_struct(png_ptr)))
    {
        png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
        return -2;
    }
 
    /* Set Error callback. */
    if (setjmp(png_jmpbuf(png_ptr)))
    {
        png_destroy_write_struct(&png_ptr, &info_ptr);
        return -3;
    }
 
    /* Initialize info for writing PNG stream to memory. */
    write_io_ptr.stream_ptr = (png_voidp)pngbuf;
    write_io_ptr.stream_len = 0;
 
    /* Set new custom write functions. */
    png_set_write_fn(png_ptr, (png_voidp)&write_io_ptr, (png_rw_ptr)user_write_data,
                     (png_flush_ptr)user_flush_data);
 
    /* Set the image size, colortype, filter type, etc... */
    bit_depth = nbits;
    color_type = PNG_COLOR_TYPE_GRAY;
    if (nbits == 24)
    {
        bit_depth = 8;
        color_type = PNG_COLOR_TYPE_RGB;
    }
    else if (nbits == 32)
    {
        bit_depth = 8;
        color_type = PNG_COLOR_TYPE_RGB_ALPHA;
    }
    png_set_IHDR(png_ptr, info_ptr, width, height,
                 bit_depth, color_type, PNG_INTERLACE_NONE,
                 PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
 
    /* Put image data into the PNG info structure. */
    bytes = nbits / 8;
    row_pointers = malloc(height * sizeof(png_bytep));
    for (j = 0; j < height; j++)
        row_pointers[j] = (png_bytep *)(data + (j * width * bytes));
    png_set_rows(png_ptr, info_ptr, (png_bytepp)row_pointers);
 
    /* Do the PNG encoding, and write out PNG stream. */
    png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
 
    /* Clean up. */
    png_destroy_write_struct(&png_ptr, &info_ptr);
    free(row_pointers);
    pnglen = write_io_ptr.stream_len;
    return pnglen;
}