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ambient occlusion + displacement mapping


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Hello folks. :)

I've noticed that ambient occlusion is extremely slow when I have displacement mapping in a scene. For example, rendering a poly-modeled character as Subdivision-Surfaces is not a problem, but as soon as I apply a displacement shader it won't even finish a single bucket.

How do you get around this? Just render a non-displaced version and comp it later? I don't imagine that would look very good. Do any other micropoly/GI capable renderers have this issue or is just a mantra thing, or is this even a problem for anyone else??

Thank you.

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Yeah, the tessellation of your mesh for raytracing is a very slow process. One optimisation you could try is to turn down your Level Of Detail on your character. This will make Mantra do less tessellation, which might or might not make your ambient occlusion worse.

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Hey Da Juice,

Unfortunately mantra can be a black box at times.. How heavy is your model? If you use straightfoward reflection against it, does it work? i.e put it on a mirrored floor in just direct lighting.

If it never renders, I reckon you should post it up to Side Effects and ask them to examine it. Or post it here too, and maybe one of us will find a moment... ;)

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Hmm, that works...well...sorta. The reflection doesn't actually show the displacement correctly. Below is a piccy, I'm using the Vex Metal shader. Argh, I just want the GI to work, I don't even care about the reflections right now.

thx for helping out btw!


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OK, I think I fixed it. Looks like the displace bound was the culprit. It was set unnessicarily high which was resulting in the insane render times. I turned it off alltogether and Ambient Occlusion works fine now. Still pretty slow, but at least not unusable.

Peace! :)

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Hey DaJuice,

You can channel reference the object's Displace Bound parameter to the Displacement Shader's Amplitude/Height/foo parameter. This removes the need to guess what the Displace Bound is plus you only have to adjust one parameter.

I hope the above helps!



PS The legs of the model looks great! :D

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