Low-level Graphics on Raspberry Pi (even more palette)

Another effect with palette: fade in/out. We can - in addition to rotating the entries - modify the palette entry RGB values on the fly and make the pixels drawn in this color to fade in or out.

Draw some background stuff (blue and white checkerboard), a black block to hold the actual piece and something to fade:

...
#define DEF_COLOR 14
#define MOD_COLOR (16 + DEF_COLOR)
...
    int x, y;
    int t = vinfo.xres / 24;

    // t x t pix black and white checkerboard
    for (y = 0; y < vinfo.yres; y++) {
        int xoffset = y / t % 2;
        for (x = 0; x < vinfo.xres; x++) {

            // color based on the tile
            int c = (((x / t + xoffset) % 2) == 0) ? 1 : 15;

            // draw pixel
            put_pixel(x, y, c);

        }
    }
    // black block in the middle
    for (y = (vinfo.yres / 2); y < (vinfo.yres / 2 + t); y++) {
        for (x = (vinfo.xres / 4 - t / 2); 
             x < (vinfo.xres / 4 * 3 + t / 2); x++) 
        {
            put_pixel(x, y, 0);
        }
    }
    // something in the color in the extended palette
    for (y = (vinfo.yres / 2 + t / 4); 
         y < (vinfo.yres / 2 + t - t / 4); y++) 
    {
        int n = 0;
        for (x = (vinfo.xres / 4); x < (vinfo.xres / 4 * 3); x++) {
            if (n % (t / 4)) {
                put_pixel(x, y, MOD_COLOR);
            }
            n++;
        }
    }
...

And then modify the associated palette entry:

...
        // fade palette entry out (to black)" and back in
        int j;
        int fps = 60; // frames per second
        int f = 255;
        int fd = -2;
        while (f < 256) {
            r[DEF_COLOR] = (def_r[14] & f) << 8;
            g[DEF_COLOR] = (def_g[14] & f) << 8;
            b[DEF_COLOR] = (def_b[14] & f) << 8;
            // change fade
            f += fd;
            // check bounds
            if (f < 0) {
                // change direction
                fd *= -1;
                f += fd;
            }
            // Note that we set up the 'pal' structure earlier
            // and it still points to the r, g, b arrays,
            // so we can just reuse 'pal' here
            if (ioctl(fbfd, FBIOPUTCMAP, &pal) != 0) {
                printf("Error setting palette.\n");
            }
            usleep(1000000 / fps);
        }
...

Compile with 'gcc -o fbtest5z fbtest5z.c' and run with './fbtest5y'. The yellow bars should fade out and back in:

...imagine for example black background and white text fading in and out... movie titles :D

Full code available in GitHub.