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PSA_Velocity displays differently GPU/CPU

For particles rendered with PSA_Velocity On CPU the size scales to some degree with speed (say pick a speed ~0.1 vice ~10) With GPU particles the visual size is constant with actual velocity

I assume this is not intended? Shouldn't both appear to be the same?

If I had to guess I would say there is a missing normalization of some vector in CPU rendering path

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asked Jan 10 '15 at 06:46 AM in Rendering

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loon8
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avatar image Lovecraft_K ♦♦ STAFF Jan 12 '15 at 07:26 PM

Hey loon8 -

Can you share screenshots of your setup? I have tried to replicate and I am not seeing any size difference in either CPU or GPU Particles with the PSA_Velocity Screen Alignment set.

Thank You

Eric Ketchum

avatar image loon8 Jan 15 '15 at 02:04 PM

Thanks for responding so quickly.

Screen shot attached, please let me know if there is anything else I can provide on this.

I looked at the code that generates the axes for the particles, in the shader files. The GPU system uses the particle velocity directly, whereas the CPU system computes the velocity by a delta between particle positions. I'm assuming its some sort of rounding/precision issue that occurs when the particle is moving very slowly

note in the screen shot two emitters both identical except for the left one (rendering to the center) is a CPU system colored white the right one (rendering above) is a GPU system colored red (and with a higher position)

You'll see the itty bitty white square from the cpu system, and a "properly" sized/shaped red block from the GPU one.

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Hey loon8 -

Thank you for the settings that help me quickly replicate the issue, I have entered the issue with our engineers and will keep you informed as we continue investigating a solution.

Thank You

Eric Ketchum

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answered Jan 15 '15 at 08:39 PM

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Lovecraft_K ♦♦ STAFF
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