Developer Notes

If the user wants to target higher framerates while not supporting "low" framerates, he can disable the feature with:
"r.GPUParticle.FixDeltaSeconds 0"

If he puts a too small value like "r.GPUParticle.FixDeltaSeconds .005", then low framerate systems will suffer extra cost because the simulation will be done several times (to the extent of "r.GPUParticle.MaxNumIterations")

This is definitely a new behavior compared with the previous version, but to some extent the system must be designed to look acceptable at framerates around 30-60 fps. This special case binding the frame rate to the particle system look is what was intented to be fixed by the FixDeltaSeconds feature (it goes for high framerates as well a "slomo" replay). Also the test case here is very specific and if there was some random put to the particle positions, it would be much harder to distinguish between the previous version and the new.


When using a GPU particle and setting a steady stream there is an obvious stutter compared to 4.10.4 where everything worked smoothly.

Regression: YES
This issue did not occur in 4.10.4 CL-2872498

Reproducible in:

  • 4.11.0 CL- 2927265
  • 4.12 Dev-Main - CL-2930868
Steps to Reproduce

1. Open UE4
2. Created a New Particle System
3. Set the Initial Velocity to -150 X for min and max value and 0 for YZ values
4. Add a GPU Emitter
5. Set the Spawn Rate to 5000

Regression: YES
This issue did not occur in 4.10.4 CL-2872498

Results: GPU Stream has a stutter

Expected: The GPU stream should be smooth

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ComponentUE - Graphics Features
Affects Versions4.114.12
Target Fix4.13
Fix Commit2960131
CreatedApr 1, 2016
ResolvedApr 28, 2016
UpdatedMay 2, 2018
View Jira Issue