pngdriver/read_bmp.c

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/*!
   \file lib/pngdriver/read_bmp.c
 
   \brief GRASS png display driver - read 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 int get_2(const unsigned char **q)
{
    const unsigned char *p = *q;
    unsigned int n = (p[0] << 0) | (p[1] << 8);
 
    *q += 2;
    return n;
}
 
static unsigned int get_4(const unsigned char **q)
{
    const unsigned char *p = *q;
    unsigned int n = (p[0] << 0) | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);
 
    *q += 4;
    return n;
}
 
static int read_bmp_header(const unsigned char *p)
{
    if (*p++ != 'B')
        return 0;
    if (*p++ != 'M')
        return 0;
 
    if (get_4(&p) != (unsigned int)HEADER_SIZE + png.width * png.height * 4)
        return 0;
 
    get_4(&p);
 
    if (get_4(&p) != HEADER_SIZE)
        return 0;
 
    if (get_4(&p) != 40)
        return 0;
 
    if (get_4(&p) != (unsigned int)png.width)
        return 0;
    if (get_4(&p) != (unsigned int)-png.height)
        return 0;
 
    get_2(&p);
    if (get_2(&p) != 32)
        return 0;
 
    if (get_4(&p) != 0)
        return 0;
    if (get_4(&p) != (unsigned int)png.width * png.height * 4)
        return 0;
 
    get_4(&p);
    get_4(&p);
    get_4(&p);
    get_4(&p);
 
    return 1;
}
 
void read_bmp(void)
{
    unsigned char header[HEADER_SIZE];
    FILE *input;
    int x, y;
    unsigned int *p;
 
    if (!png.true_color)
        G_fatal_error("PNG: cannot use BMP with indexed color");
 
    input = fopen(png.file_name, "rb");
    if (!input)
        G_fatal_error("PNG: couldn't open input file %s", png.file_name);
 
    if (fread(header, sizeof(header), 1, input) != 1)
        G_fatal_error("PNG: invalid input file %s", png.file_name);
 
    if (!read_bmp_header(header))
        G_fatal_error("PNG: invalid BMP header for %s", png.file_name);
 
    for (y = 0, p = png.grid; y < png.height; y++) {
        for (x = 0; x < png.width; x++, p++) {
            int b = fgetc(input);
            int g = fgetc(input);
            int r = fgetc(input);
            int a = fgetc(input);
            unsigned int c = png_get_color(r, g, b, a);
 
            *p = c;
        }
    }
 
    fclose(input);
}