#define RLUM    (0.3086)
#define GLUM    (0.6094)
#define BLUM    (0.0820)

// Graphica Obscure
#define GO_RGB_TO_GREY(r, g, b) ((int)((RLUM * (double)r) + (GLUM * (double)g) + (BLUM * (double)b)))

static inline unsigned char pu_clamp(int x) {
    return (x > 255) ? 255 : (x < 0 ? 0 : x);
}

static GdkPixbuf *pixbuf_tint(GdkPixbuf *src, GdkPixbuf *dest, int r, int g, int b, int alpha) {
    int s_has_alpha, d_has_alpha;
    int s_width, s_height, s_rowstride;
    int d_width, d_height, d_rowstride;
    guchar *s_pix, *sp;
    guchar *d_pix, *dp;
    int i, j, pix_width, grey;

    g_return_val_if_fail(src != NULL, NULL);
    g_return_val_if_fail(dest != NULL, NULL);

    s_width = gdk_pixbuf_get_width(src);
    s_height = gdk_pixbuf_get_height(src);
    s_has_alpha = gdk_pixbuf_get_has_alpha(src);
    s_rowstride = gdk_pixbuf_get_rowstride(src);
    s_pix = gdk_pixbuf_get_pixels(src);

    d_width = gdk_pixbuf_get_width(dest);
    d_height = gdk_pixbuf_get_height(dest);
    d_has_alpha = gdk_pixbuf_get_has_alpha(dest);
    d_rowstride = gdk_pixbuf_get_rowstride(dest);
    d_pix = gdk_pixbuf_get_pixels(dest);

    g_return_val_if_fail(d_width == s_width, NULL);
    g_return_val_if_fail(d_height == s_height, NULL);
    g_return_val_if_fail(d_has_alpha == s_has_alpha, NULL);

    pix_width = (s_has_alpha ? 4 : 3);

    for (i = 0; i < s_height; i++) {
        sp = s_pix;
        dp = d_pix;

        for (j = 0; j < s_width; j++) {
            grey = GO_RGB_TO_GREY(sp[0], sp[1], sp[2]);

            dp[0] = pu_clamp(pu_clamp(((int) grey + r) * alpha / 255) +
                             pu_clamp((int) sp[0] * (255 - alpha) / 255));    /* red */

            //fprintf(stderr, "alpha=%i, r=%i, grey=%i -> %i + %i = %i\n", alpha, r, grey, pu_clamp(((int)grey + r) * alpha / 255), pu_clamp((int)sp[0] * (255 - alpha) / 255), dp[0]);	/* red */

            dp[1] = pu_clamp(
                    pu_clamp((grey + g) * alpha / 255) + pu_clamp((int) sp[1] * (255 - alpha) / 255));    /* green */
            dp[2] = pu_clamp(
                    pu_clamp((grey + b) * alpha / 255) + pu_clamp((int) sp[2] * (255 - alpha) / 255));    /* blue */

            if (s_has_alpha) {
                dp[3] = sp[3];    /* alpha */
            }

            dp += pix_width;
            sp += pix_width;
        }

        d_pix += d_rowstride;
        s_pix += s_rowstride;
    }

    return dest;
}