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mental ray notes

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Hey Kids,

Although it doesn't apply directly, there is a mental ray shader

primer that was posted on the Houdini list.


written by Hwee K, pretty interesting.

Just curious, anyone out there using mental ray? I may be working

at a shop that has a lot of mental ray licenses, and was curious what

your opinons were about houdini and mentalray?



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Mental Ray works well with Houdini, and is a spanking renderer.

Mantra should take the cue from MR and start to sample shaders with rays rather than micro-vertices; that would remove one of the biggest chores of shader-writing -- anti-aliasing.

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Hey Hwee,

How does raytracing shaders (which IS possible in mantra) help with anti-aliasing? Surely its actually a lot worse, since the surface derivatives are not as accurate as with micropolygon rendering?



PS. I know VERY little about how mental ray renders:)

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Both Mantra and PRman decouple geometric sampling from shading sampling, while MR makes no distinction between the two. In MR, 16 (for eg.) sampling rays get sent out and each returns a different geometric hit point as well as different shader return value, and they all get filtered in the same trusty way. On the other hand, in Mantra and PRman, some of those rays could return the same shading value because they hit the same micropolygon.

So, Du and Dv are not as important in MR and there's no need to fret over their accuracy. In fact, because there's no notion of a "micro-shading-facet" in MR, there's no notion of Du and Dv!

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