Dithering based fading in Quake 2

quake2_fade_dithering.c

// https://github.com/id-Software/Quake-2/blob/372afde46e7defc9dd2d719a1732b8ace1fa096e/ref_soft/r_draw.c#L428
void Draw_FadeScreen (void)
{
	int			x,y;
	byte		*pbuf;
	int	t;

	for (y=0 ; y<vid.height ; y++)
	{
		pbuf = (byte *)(vid.buffer + vid.rowbytes*y);
		t = (y & 1) << 1;

		for (x=0 ; x<vid.width ; x++)
		{
			if ((x & 3) != t)
				pbuf[x] = 0;
		}
	}
}