Operating system: 4.20.12-gentoo Linux
Graphics card: Radeon(TM) Pro WX9100 (VEGA10, DRM 3.27.0, 4.20.12-gentoo, LLVM 6.0.1)
Broken: 2.80 (sub 48) commit hash: bf9904ec8018 Build: 2019-03-13 01:14:16 Linux Release branch: blender2.7
Worked: (optional) 2.79b commit hash and date unknown; compiled from Gentoo repository
Short description of error
Fails to make a valid particle cache when rendering a dynamic hair system via Cntl + F12. Hair particle motion appears compromised after the first frame. see video clip dyn_on.mkv.
A .blend file with a mesh object that has a hair particle system defined on it. Hair dynamics is turned on in the particle system properties panel. The file should have been previously saved without a cache. Blend file dyn_on.blend provided for this requirement.
Exact steps for others to reproduce the error
- Open dyn_on.blend
- Cntl + F12 to render animation (implicitly build in-memory cache)
- Observe: a. Cache indicator on timeline shows only 1 or 2 valid initial frames; remaining 248 - 249 frames are invalid. b. Hair particles exhibit only limited rotational dynamics. They do not follow the surface of the sphere (i.e., they appear "unanchored"), nor do they seem affected by gravity. See dyn_on.mkv video clip. c. After the last frame has been rendered, click on the rewind control in the timeline. The cache section in the Particles properties reports the state of the cache: "1 frames in memory (216 KB), not exact since frame 0"
- Bake particle dynamics first or
- Run the animation through in the 3D viewport to create an in-memory or on disk cache before rendering.
Rendering with an in-memory, on-disk, or with baked dynamics appears to generate an unaffected animation. See dyn_on_cache.mkv video clip.
- Examples rendered in Cycles, but EEVEE and Workbench rendering does not change behavior.
- Hair particles rendered with a collection of simple mesh geometry in the examples, but rendering with single mesh objects or rendering hair paths does not change behavior.
- Running in single thread mode (-t 1 on command line) does not change behavior.
- Rendering via CPU or GPU does not change behavior.
- Problem seems specific to hair particle systems. Emitter particle systems without pre-computed caches can be rendered with Cntl + F12; the cache seems fully valid in the time line, dynamics of falling emitter particles do not seem unusual and the cache section in the Particles properties reports that there are 250 valid frames in memory at the conclusion of the animation.
T62439 describes a failure in particle updates which seems very similar in appearance exhibited by particles in video clip dyn_on.mkv.