Step 1:

Essentially to make the blue pixel teleport to the opposite borders upong detecting boundries collision, we simply detect when the pixel reaches, say the right most border which is x = 800, then we simple move (teleport) the location of the pixel to x = 0.

So an rough example of the code would be:

if (pixel.x > 800) {
	pixel.x = 0;
}

if (pixel.y < 0) {
	pixel.y = 600;
}
			

Exercise

Do teleportation for all sides of the map.