They aren't..... Some popular shortcuts include: - Cut at n hops (with n=4 or n=8 popular choices), defaulting to "ambient" light after that - Give each mate

They aren't..... Some popular shortcuts include: - Cut at n hops (with n=4 or n=8 popular choices), defaulting to "ambient" light after that - Give each material an "ambient" color, so that you don't actually need to trace every pixel back into every light source (just into e.g. spotlights) - Solve a radiosity equation for the surface colors, and trace rays for textures/reflections. Complete ray tracing is, indeed, insane - in fact, to get high quality pictures and avoid aliasing, most ray tracers send multiple rays through every picture and average the result.