cairodriver/read_ppm.c

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#include "cairodriver.h"

void read_ppm(void)
{
    char *mask_name = G_store(file_name);
    FILE *input, *mask;
    int x, y;
    int i_width, i_height, maxval;

    input = fopen(file_name, "rb");
    if (!input)
        G_fatal_error("cairo: couldn't open input file %s", file_name);

    if (fscanf(input, "P6 %d %d %d", &i_width, &i_height, &maxval) != 3)
        G_fatal_error("cairo: invalid input file %s", file_name);

    fgetc(input);

    if (i_width != width || i_height != height)
        G_fatal_error
            ("cairo: input file has incorrect dimensions: expected: %dx%d got: %dx%d",
             width, height, i_width, i_height);

    mask_name[strlen(mask_name) - 2] = 'g';

    mask = fopen(mask_name, "rb");
    if (!mask)
        G_fatal_error("cairo: couldn't 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 != width || i_height != height)
        G_fatal_error
            ("cairo: input mask file has incorrect dimensions: expected: %dx%d got: %dx%d",
             width, height, i_width, i_height);

    G_free(mask_name);

    for (y = 0; y < height; y++) {
        unsigned int *row = (unsigned int *)(grid + y * stride);

        for (x = 0; x < 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);
}