3 ms·

It's vaguely analogous to why ray tracing goes backwards.

• TeMPOraL 5d ago
  Which is also not obvious especially given the way it's presented is that it goes forwards. The naive explanation from the top of my mind (I used to know it better years ago, when I was toying with writing raytracers): because viewport is fixed, an it's much less rays to trace if you cast from viewport pixels in various directions, than if you cast from light sources in every direction and throw away ~99% of them as they never pass through the viewport. Plus, you get spatially uniform image this way, whereas realistic take would oversample the bright parts before giving you any samples for the dark parts.