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Pyro Shader noise/displace


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I have some trouble using the noise and displacement option of the pyro shader.

It seems to add nice detail on my smoke sims, but render time are increasing a lot.


For a basic scene (no noise/no disp), render time is multiply by at least 5-10 times with noise, and even more with displacement.


I think i've done things most straightforward way :

- for noise i've just activate noise field in pyro shader

- for disp, activate disp under shading and compute N in sop with a volume gradient (amplitude on density field)


Is this increased render time normal? I feel that increasing sim Res is less expensive than adding detail in post..


Thanks in advance !


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hi, after adding displacement you can definitely expect increased render times. 5-10 times seems to be too much though. displacement is multiplying amount of data renderer needs to compute so its easy to overkill it with too high setting either on displacements or somewhere else. try to render with very low settings first (number of recursions and advection on displace noise, also different type of noises might do a big difference, volume quality affects the render speed greatly, too many raytrace samples can kill it totally without any visual enhancement, testing different stochastic trasparency settings on mantra is a good idea too) and gradually add more detail. that might help to isolate the problem.


also, are you rendering with pbr or micropolygon/raytrace? raytrace should be much faster than pbr with volumes and gives me usualy the best results. micropoly is generaly the fastest way to go and can handle huge amount of volume data but detail and mblur tends to be not as nice as with raytrace. try to avoid using raytraced shadows with transparency. especially on enviro lights its a real killer for volumes. 

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Sticking to pbr actually, as i'm more confident with it. ll definitly give raytrace a try.

Not using env light as i'm rendering rgb pass only for relighting. Raytraced shadows seems much faster than deep (generation time is pretty huge for deep here!)


About rendering time, i understand that displacement is slower to compute, but what about simple noise (pyro shader/smoke/noise field).

It seems to be just a density multiplier on density field (advected with rest field), so why is it as slow compare to simple density without noise? (at least 5 time slower was for the noise option!)


Thanks !

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with shadows, yes, in some cases raytraced shadows may be faster than shadows maps. however, generally, in principle shadow maps are more efficient since it allows you to interpolate. raytraced shadows may generate lot of noise in volumes that you can only clean out by using more samples (which is not always what you need or can afford).


using noise in displacement is not a simple density multiplier. it is a proper displacement used on volume. therefore you are generating more data to get the extra detail. its similar to upresing your sim but it happens in rendertime without actualy simulating anything. 

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oh, then youre not talking about displacement at all :) since you mentioned displacement at the first post i thought its the displacement youre having problems with. regarding to field noise in density, i have never used it. as far as i know, its very clumsy to work with (bcs of stretching over the fluid) and generally it seems to be better to upres the sim if you can afford it. 

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