On the right side, you see new pixels being painted only if they are lighter than the pixels they are painted over. It shows that this is happening for every tr

On the right side, you see new pixels being painted only if they are lighter than the pixels they are painted over. It shows that this is happening for every triangle, regardless of what order the triangles are iterated over. This is a visualization. If you already know how it works, so what? Now you have a visualization of it that isn't confined to your brain.