cairodriver/read_ppm.c

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/*!
   \file lib/cairodriver/read_ppm.c
 
   \brief GRASS cairo display driver - read PPM image (lower level functions)
 
   SPDX-FileCopyrightText: 2007-2008, 2011 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_read_ppm(void)
{
    char *mask_name = G_store(ca.file_name);
    FILE *input, *mask;
    int x, y;
    int i_width, i_height, maxval;
 
    input = fopen(ca.file_name, "rb");
    if (!input)
        G_fatal_error(_("Cairo: unable to open input file <%s>"), ca.file_name);
 
    if (fscanf(input, "P6 %d %d %d", &i_width, &i_height, &maxval) != 3)
        G_fatal_error(_("Cairo: invalid input file <%s>"), ca.file_name);
 
    if (fgetc(input) == EOF)
        G_fatal_error(_("Cairo: unexpected EOF reading <%s>"), ca.file_name);
 
    if (i_width != ca.width || i_height != ca.height)
        G_fatal_error(_("Cairo: input file has incorrect dimensions: "
                        "expected: %dx%d got: %dx%d"),
                      ca.width, ca.height, i_width, i_height);
 
    mask_name[strlen(mask_name) - 2] = 'g';
 
    mask = fopen(mask_name, "rb");
    if (!mask)
        G_fatal_error(_("Cairo: unable to open input mask file <%s>"),
                      mask_name);
 
    if (fscanf(mask, "P5 %d %d %d", &i_width, &i_height, &maxval) != 3)
        G_fatal_error(_("Cairo: invalid input mask file <%s>"), mask_name);
 
    if (fgetc(mask) == EOF)
        G_fatal_error(_("Cairo: unexpected EOF reading mask <%s>"), mask_name);
 
    if (i_width != ca.width || i_height != ca.height)
        G_fatal_error(_("Cairo: input mask file has incorrect dimensions: "
                        "expected: %dx%d got: %dx%d"),
                      ca.width, ca.height, i_width, i_height);
 
    G_free(mask_name);
 
    for (y = 0; y < ca.height; y++) {
        unsigned int *row = (unsigned int *)(ca.grid + y * ca.stride);
 
        for (x = 0; x < ca.width; x++) {
            int r = fgetc(input);
            int g = fgetc(input);
            int b = fgetc(input);
            int a = fgetc(mask);
 
            r = r * 255 / maxval;
            g = g * 255 / maxval;
            b = b * 255 / maxval;
            a = a * 255 / maxval;
 
            if (a > 0 && a < 0xFF) {
                r = r * a / 0xFF;
                g = g * a / 0xFF;
                b = b * a / 0xFF;
            }
 
            row[x] = (a << 24) | (r << 16) | (g << 8) | (b << 0);
        }
    }
 
    fclose(input);
    fclose(mask);
}