Kent Tramell discovered that using bump maps causes a huge increase in Cycles rendering time and shows a way to avoid this penalty.
There’s at least one thing that unites every single 3D artist: The dream of faster render times. It can be a major buzz-kill that after accomplishing a CG scene through blood, sweat and tears, you end up waiting hours to see a final render. In this video I’ll share a little trick to speed up your materials’ render times!The Trick:
Bump maps can significantly hinder render computation. Despite the fact that they are an illusion that don’t actually displace geometry, Cycles allows the illusion to affect light bouncing and global illumination. Therefore, if we exclude our bump maps from being computed by in global illumination we can save significant render time. See exactly how tp do this with the Light Path node in the video above!
5 Comments
This is great. Most useful thing I have seen in a while!
hmmm......
I have to try this.
Thank you for the tip Kent!
Been playing with some brick patterns & had hoped this might improve my render tests. Unfortunately time has increased from 7:47 to 8:24. Perhaps the number of objects and groups sharing the texture is influencing this (?)
Very counterproductive on a simple scene like this:
Sphere with texture bump, put over a simple plane L shaped as a studio setup, 3 emitter planes (top, left, right).
Sorry but before hail as a miracle, and announce it with fanfare waving the 30% flag in the face of people hungry for performances we should test it on a range of scenes to understand how it works.
First thing I thought when I saw this was wow, then: why didn't I think of that!? Then I went away and tested.
I'm working on a simple scene which is kind of slow to render, or more accurately, because of the type of scene it is, an indoors scene using area lamps as windows, it takes longer to clean up the noise, because of the light bouncing off the floor, walls and ceiling. This type of scene always takes more samples to get relatively noise free, and my scene has bump and (material) displacement all over the place, so I tested it.
First I rendered out without the trick, twice, to exclude any BVH caching times, etc., then I made a node group, and inserted it before all of the bump nodes on all of the shaders, and rendered, then I did the same on the displacements, then I kept the groups in-place, but turned them off and rendered. I did this with both the path tracing and branched path.
I can only report what happened.
The times increased in all cases.
Branched path times:
Without trick: 6.12
With trick on bumps only: 7.08
With trick on bumps and displacements: 7.26
Group inplace, but turned off: 6.38
Similar results with path tracing. The renders didn't clean up any either, I thought it might help with noise coming from bump which is then bounced, but no. Maybe using a 'bounce limiter' on the bumps instead...?
Disappointing, but maybe it will work with other scenes, if so, I'll post those results too.