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)

  (C) 2007-2008, 2011 by Lars Ahlzen and the GRASS Development Team
  
  This program is free software under the GNU General Public License
  (>=v2). Read the file COPYING that comes with GRASS for details.
  
  \author Lars Ahlzen <lars ahlzen.com> (original contibutor)
  \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);

    fgetc(input);

    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);

    fgetc(mask);

    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);
}