Add biased/unbiased indicator in Render Settings dialog

[Mango-3]

Not sure if this is really a good idea. Many user probably don't have a good understanding what biased/unbiased means and even with (unbiased) vanilla path-tracing, the use of selective ray-clamping, bounce limits, low-light threshold or roughness clamping introduces some bias. Even bidir-path tracing with Metropolis sampling is biased (startup-bias). And SPPM is biased but consistent, it converges to the correct solution given enough time/samples.

[dictoon]

It's useful when doing predictive rendering to make sure that the rendering settings aren't introducing obvious bias: if you forget to disable Max Ray Intensity, the render will be obviously biased. In appleseed, only path tracing (unidirectional or bidirectional) with the proper settings (no MRI, no bounce limits, etc.) should be indicated as "unbiased".

That said it's not a very important feature.

[Mango-3]

Relevant links for information: https://www.ci.i.u-tokyo.ac.jp/~hachisuka/misc.pdf https://www.chaosgroup.com/blog/the-truth-about-unbiased-rendering

[Mango-3]

Just a note. Also settings for the scene lights, e.g. cast_shadows and cast_indirect_light needs to be checked if they are set to true (for all enabled light sources) and ray visibility flags for objects.