pngdriver/write_bmp.c

Go to the documentation of this file.

/*!
   \file lib/pngdriver/write_bmp.c
 
   \brief GRASS png display driver - write bitmap (lower level functions)
 
   SPDX-FileCopyrightText: 2007-2014 Glynn Clements
   SPDX-FileCopyrightText: GRASS Development Team
   SPDX-License-Identifier: GPL-2.0-or-later
 
   \author Glynn Clements
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#include <grass/gis.h>
#include "pngdriver.h"
 
static unsigned char *put_2(unsigned char *p, unsigned int n)
{
    *p++ = n & 0xFF;
    n >>= 8;
    *p++ = n & 0xFF;
    return p;
}
 
static unsigned char *put_4(unsigned char *p, unsigned int n)
{
    *p++ = n & 0xFF;
    n >>= 8;
    *p++ = n & 0xFF;
    n >>= 8;
    *p++ = n & 0xFF;
    n >>= 8;
    *p++ = n & 0xFF;
    return p;
}
 
static void make_bmp_header(unsigned char *p)
{
    *p++ = 'B';
    *p++ = 'M';
 
    p = put_4(p, HEADER_SIZE + png.width * png.height * 4);
    p = put_4(p, 0);
    p = put_4(p, HEADER_SIZE);
 
    p = put_4(p, 40);
    p = put_4(p, png.width);
    p = put_4(p, -png.height);
    p = put_2(p, 1);
    p = put_2(p, 32);
    p = put_4(p, 0);
    p = put_4(p, png.width * png.height * 4);
    p = put_4(p, 0);
    p = put_4(p, 0);
    p = put_4(p, 0);
    p = put_4(p, 0);
}
 
void write_bmp(void)
{
    unsigned char header[HEADER_SIZE];
    FILE *output;
    int x, y;
    unsigned int *p;
 
    output = fopen(png.file_name, "wb");
    if (!output)
        G_fatal_error("PNG: couldn't open output file %s", png.file_name);
 
    memset(header, 0, sizeof(header));
    make_bmp_header(header);
    fwrite(header, sizeof(header), 1, output);
 
    for (y = 0, p = png.grid; y < png.height; y++) {
        for (x = 0; x < png.width; x++, p++) {
            unsigned int c = *p;
            int r, g, b, a;
 
            png_get_pixel(c, &r, &g, &b, &a);
 
            fputc((unsigned char)b, output);
            fputc((unsigned char)g, output);
            fputc((unsigned char)r, output);
            fputc((unsigned char)a, output);
        }
    }
 
    fclose(output);
}