mergecloth.c from FreePop at Krugle

Show mergecloth.c syntax highlighted

// Merge images to produce background and overlay images.
// By Brendon Higgins: bh_doc@users.sourceforge.net
// Released in Nov 2003 under GPL. See www.gnu.org if you don't know what that is.

// 2005-06-24: Made changes so that now the overlay is always completely white
// with a varying alpha channel. The input pictures now must both be shaded -
// ie a shaded red colour with white background and a shaded blue colour with
// a black background. This should make things easier.

#include <stdio.h>
#include <pngio.h>

// Clip an integer to the range of a normal 8-bit colour channel.
unsigned char clip(int x) {
    if (x > 255) return 255;
    if (x < 0) return 0;
    return x;
}

colour calc_over(colour red, colour blue) {
    colour col;
    col.red = col.green = col.blue = 255;
    col.alpha = clip((int)red.red - red.green - blue.red + blue.green);
    return col;
}

colour calc_back(colour red, colour blue) {
    colour col;
    int x = red.red - blue.red - 255;
    int y;
    if (x == 0) {
        col.red = 255;
        col.green = 255;
        col.blue = 255;
        col.alpha = 0;
    } else {
        col.red = clip(-(int)blue.red * 255 / x);
        col.green = clip(-(int)blue.green * 255 / x);
        col.blue = clip(((int)red.green - red.blue - blue.green) * 255 / x);
        y = (int)red.red - red.green - blue.red + blue.green - 255;
        if (y == 0) {
            col.alpha = 255;
        } else {
            col.alpha = clip(x * 255 / y);
        }
    }
    return col;
}

int main(int argc, char* argv[]) {
    pngstuff red, blue;

    int x, y, width, height, ok;
    unsigned char al, c;

    colour** rows_col;
    colour** rows_back;

    if (argc != 5) {
        printf("Merges the colours of two special pictures to produce an alpha mapped overlay\n");
        printf("for the cloth of those pictures, and a background picture.\n");
        printf("Writes to the files given the pictures with the alpha information.\n");
        printf("One picture must have a red cloth with a white background,\n");
        printf("the other a blue cloth with a black background.\n\n");
        printf("Usage:\n   mergecloth <redwhitepic> <blueblackpic> <overlayoutpic> <backoutpic>\n\n");
        printf("Input and output must be PNG.\n\n");
        return 1;
    }

    printf("mergecloth: %s & %s -> %s & %s ... ", argv[1], argv[2], argv[3], argv[4]);

    if (open_png(argv[1], &red) != 0) {
        printf("Error reading %s", argv[1]);
        return 2;
    }
    if (open_png(argv[2], &blue) != 0) {
        printf("Error reading %s", argv[2]);
        close_png(&red);
        return 3;
    }

    width = png_get_image_width(red.png, red.info);
    height = png_get_image_height(red.png, red.info);

    // TODO Check malloc != NULL
    rows_col = (colour**) malloc(height * sizeof(colour*));
    rows_back = (colour**) malloc(height * sizeof(colour*));
    for (y = 0; y < height; ++y) {
        rows_col[y] = (colour*) malloc(width * sizeof(colour));
        rows_back[y] = (colour*) malloc(width * sizeof(colour));
        for (x = 0; x < width; ++x) {
            rows_col[y][x] = calc_over(red.rows[y][x], blue.rows[y][x]);
            rows_back[y][x] = calc_back(red.rows[y][x], blue.rows[y][x]);
        }
    }

    ok = 0;
    if (write_png(argv[3], rows_col, width, height) != 0) {
        printf("Error writing %s", argv[3]);
        ok = 4;
    }
    if (write_png(argv[4], rows_back, width, height) != 0) {
        printf("Error writing %s", argv[4]);
        ok = 5;
    }

    for (y = 0; y < height; ++y) {
        free(rows_col[y]);
        free(rows_back[y]);
    }
    free(rows_col);
    free(rows_back);

    close_png(&red);
    close_png(&blue);

    if (ok == 0) {
        printf("Done\n");
    } else {
        return ok;
    }

    return 0;
}
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