Volume Sampling & Render Delays

[petkovic]

Hi everyone, i have a question since i dont understand why does it take so long to render a simple scene when Use Maya Vol Sampling is on... (with mr)

When Vol Sampling is off, render is 18sec, but when its ON it ~5min, also the cpu usage was at 0% (not sure whats going on and why is cpu 0, and thats takes a while, and its really annoying), just when the render started it was a 100%.

so i did some tests with other renders:
- with arnold render starts immediately, no delays or anything...
- with vray render there is also some kind of delay, where cpu is 0%

so my questions are:
- can you speed up the Vol Sampling, or remove it (find some work around)
- can you remove the delays, as i remember in 3ds this goes way way faster, no delays or anything, especially with scanline render.

i can post an example scene if need it...

[dinom]

Hi petkovic

Hi everyone, i have a question since i dont understand why does it take so long to render a simple scene when Use Maya Vol Sampling is on... (with mr)
When Vol Sampling is off, render is 18sec, but when its ON it ~5min,

Volume sampling changes the way in which renderer processes objects with volume shading. Normally, volume shader (such as FumeFXshader) would be called (by renderer) only once per pixel sample; tracing through volume is then left to the shader. With volume sampling on however, shader gets called many times per pixel sample, at different depths, and it's up to renderer to combine all the samples to produce pixel color.

Main use of volume sampling (to my knowledge) is to solve the problem of geometry objects intersecting volume object. If you have a geometry object inside volume object, scene might be rendered incorrectly; geometry object might be drawn behind volume object. Volume sampling solves that problem by letting renderer "sample" volume object at different depths and placing geometry object in the right place (inside the volume object).

As you can see, volume sampling has little to do with us.

also the cpu usage was at 0% (not sure whats going on and why is cpu 0, and thats takes a while, and its really annoying), just when the render started it was a 100%.

Again, this has little to do with us.

so i did some tests with other renders:
- with arnold render starts immediately, no delays or anything...
- with vray render there is also some kind of delay, where cpu is 0%

Both arnold and vray renderers ignore volume samples parameter; no point turning it on. They work in a very different way than mental ray, so that parameter makes no sense for them; they have other means for achieving same goal.

so my questions are:
- can you speed up the Vol Sampling, or remove it (find some work around)

Sure you can; there's a parameter named "Samples multiplier" right under "Use Maya Volume Sampling" checkbox in "General parameters" rollout in "Rendering settings" rollout. By default it's set to "100%", but you can set it lower as long as you're not getting any rendering artifacts.

Cheers

[petkovic]

Hi Din

i understand everything you just wrote, but if you compare the render speed with 3ds scanline render and maya's mr render you will notice a BIG difference...

that's the only 'bad' thing about maya, everything else is great

thx & cheers