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Roja Huchez avatar image
Roja Huchez asked ·

Randomwalk2 SSS Object scale / Scene scale in HTOA

Hi Guys,


What do you think I can do to remedy this total discrepancy between GPU and CPU Randomwalk2 SSS in HTOA?


Importing a character mesh from Maya (180cm tall) to Houdini, and scaling in Houdini to 0.01 units which brings the character to 1.8m tall in Houdini.


GPU renders standard_skin Randomwalk2 subsurface (subsurface scale set to 0.001) like this:



Now SWITCH TO CPU and:



CPU renders standard_skin Randomwalk2 subsurface (exact same scale as above set to 0.001) and for this quick test looks how it should (along with my terrible lighting)


Here are the sss settings along with the transform sop displayed below.



Brought this up in another thread and thought it was my mistake but now I don't think it is.


What can I try? Something with the Houdini scale settings?


~Roja



standard surfaceskin
7273-cpu.png (570.2 KiB)
7273-gpu.png (719.3 KiB)
7273-transform.png (110.2 KiB)
1591720968764.png (30.6 KiB)
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Jamie Portsmouth avatar image
Jamie Portsmouth answered ·

Hi Roja,


Just to be clear, does the discrepancy not occur if the uniform scale is not done? (For example, if the transform is frozen into the mesh).

If you have the time, getting a minimal test case (exported ASS file) with a cube + no textures that exhibits roughly the same discrepancy would be very helpful.


Best,

Jamie

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Thanks for looking into this Jamie - much appreciated!


Houdini.hip file, exported .ass, and Arnold logs included for CPU/GPU in case those help as well.


CPU_vs_GPU_scale.zip

CPU SSS looks awesome when scaled - hopefully if anything we can get the look of the CPU version when using GPU as the render device.


GPUCPU

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cpu-vs-gpu-scale.zip (111.7 KiB)
cpu-vs-gpu-scale.zip (111.7 KiB)
gpu-sss.png (1.3 MiB)
cpu-sss.png (955.8 KiB)
Roja Huchez avatar image
Roja Huchez answered ·

* Bump


Anyone?


I built a quad gpu machine to buy and use arnold GPU in houdini and I can't right now unless this is resolved.


Would be amazing to have one of the pros solve this.


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And if you don't scale? Same problem?

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Roja Huchez avatar image Roja Huchez Stephen Blair ♦♦ ·

If I don't scale there is not problem at all - GPU = CPU, which is weird.


I need to scale the object into real world units for sim though otherwise I'd just render at 100x scale, (which is not optimal)

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