There is TraShadow. But is there MirShadow too?


Rays bounce off objects - thus we see objects.

Rays - that bounce into the camera - bounce off mirrors (after they bounce off objects) - thus we see reflections of objects.

Why don’t rays - that don’t bounce into the camera - bounce off mirrors?

In other words: Why don’t rays bounce off objects (after they bounce off mirrors)?

In the picture: Why doesn’t light from the lamp in the near end of the corridor bounce off the mirror half-way and light the far end of the corridor?

In my opinion: This is because mirrors don’t care about rays that come directly from the lamp. They only care about rays that bounce off objects.

What am I doing wrong?


And what exactly is the use of rays that don’t reach the camera?

What you want are caustics. In case you haven’t noticed, there’s a “slight” problem…for many light sources (basically all except area lights) you cannot even find such reflection rays for a given surface point, unless you assume all mirrors are perfectly flat (which is a really bad assumption…)

You need either photon maps or other GI methods like MLT to efficiently create caustics (and the “efficiency” of MLT is still very debatable…)

I haven’t put this theory to the test, but you could try turning up the ref (which is reflective) slider on your diffuse shader. Try using fresnel. If that doesn’t work then enable ray mirror for the checker board material in the areas that you want to reflect light (you’ll have to make them single user in ordrer to do so) and set it to a much lower mirror value than the mirror object.