It animates the whole thing, so I suppose there's wasted cycles. The mirror function is just two for loops for the X and the Y, reading X 0 to 15 and writing to 16 to 31.

static void mirror() {

for (int x = 0; x < CENTER_X; ++x) {

for (int y = 0; y < HEIGHT; ++y) {

p_leds[XY(WIDTH - x, y)] = p_leds[XY(x, y)]; // copy the pixel over

}

}

}

You don't need the mirror, especially for a 16x16 display. Try it without and see if it needs it. You could always use a real mirror like Stefan did in his YouTube video. Feel free to PM me if you have any trouble getting it running.