cairodriver/write_ppm.c

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/*!
   \file lib/cairodriver/write_ppm.c
 
   \brief GRASS cairo display driver - write PPM image (lower level functions)
 
   SPDX-FileCopyrightText: 2007-2008 Lars Ahlzen
   SPDX-FileCopyrightText: GRASS Development Team
   SPDX-License-Identifier: GPL-2.0-or-later
 
   \author Lars Ahlzen <lars ahlzen.com> (original contributor)
   \author Glynn Clements
 */
 
#include <grass/glocale.h>
 
#include "cairodriver.h"
 
void cairo_write_ppm(void)
{
    char *mask_name = G_store(ca.file_name);
    FILE *output, *mask;
    int x, y;
 
    output = fopen(ca.file_name, "wb");
    if (!output)
        G_fatal_error(_("Cairo: unable to open output file <%s>"),
                      ca.file_name);
 
    mask_name[strlen(mask_name) - 2] = 'g';
 
    mask = fopen(mask_name, "wb");
    if (!mask)
        G_fatal_error(_("Cairo: unable to open mask file <%s>"), mask_name);
 
    G_free(mask_name);
 
    fprintf(output, "P6\n%d %d\n255\n", ca.width, ca.height);
    fprintf(mask, "P5\n%d %d\n255\n", ca.width, ca.height);
 
    for (y = 0; y < ca.height; y++) {
        const unsigned int *row =
            (const unsigned int *)(ca.grid + y * ca.stride);
 
        for (x = 0; x < ca.width; x++) {
            unsigned int c = row[x];
            int a = (c >> 24) & 0xFF;
            int r = (c >> 16) & 0xFF;
            int g = (c >> 8) & 0xFF;
            int b = (c >> 0) & 0xFF;
 
            if (a > 0 && a < 0xFF) {
                r = r * 0xFF / a;
                g = g * 0xFF / a;
                b = b * 0xFF / a;
            }
 
            fputc((unsigned char)r, output);
            fputc((unsigned char)g, output);
            fputc((unsigned char)b, output);
            fputc((unsigned char)a, mask);
        }
    }
 
    fclose(output);
    fclose(mask);
}