source: trunk/WRF.COMMON/WRFV3/external/io_grib2/g2lib/enc_png.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <png.h>
#include "proto.h"

#ifdef __64BIT__
  typedef int g2int;
#else
  typedef long g2int;
#endif

struct png_stream {
   unsigned char *stream_ptr;     /*  location to write PNG stream  */
   g2int stream_len;               /*  number of bytes written       */
};
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)
/*
        Custom write function used to that libpng will write
        to memory location instead of a file on disk
*/
{
     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;
/*     printf("SAGwr %ld %ld %x\n",offset,length,ptr);    */
     /*for (j=offset,k=0;k<length;j++,k++) ptr[j]=data[k];*/
     memcpy(ptr+offset,data,length);
     mem->stream_len += length;
}


void user_flush_data(png_structp png_ptr)
/*
        Dummy Custom flush function
*/
{
   int *do_nothing=NULL;
}


int ENC_PNG(char *data,g2int *width,g2int *height,g2int *nbits,char *pngbuf)
{
 
    int color_type;
    g2int j,bytes,pnglen,bit_depth;
    png_structp png_ptr;
    png_infop info_ptr;
//    png_bytep *row_pointers[*height];
    png_bytep **row_pointers;
    png_stream write_io_ptr;

/* create and initialize png_structs  */

    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, (png_voidp)NULL, 
                                      NULL, NULL);
    if (!png_ptr)
       return (-1);

    info_ptr = png_create_info_struct(png_ptr);
    if (!info_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,(voidp)&write_io_ptr,(png_rw_ptr)user_write_data,
                    (png_flush_ptr)user_flush_data);
/*    png_init_io(png_ptr, fptr);   */
/*    png_set_compression_level(png_ptr, Z_BEST_COMPRESSION);  */

/*     Set the image size, colortype, filter type, etc...      */

/*    printf("SAGTsettingIHDR %d %d %d\n",*width,*height,bit_depth); */
    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=bit_depth/8;*/
    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;

}