Particle system children sometimes not generated on reload #43427
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Reference: blender/blender#43427
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Hair systems with heavy child calculation doesn't show up after reload (somewhat randomly), until explicitly reloading texture images.
This happens regularly with the victor character of the Gooseberry project (file is too heavy to upload here).
The reason seems to be that the particle system expects image textures to lazy-load image buffers on request during the creation of child hair paths:
https://developer.blender.org/diffusion/B/browse/master/source/blender/blenkernel/intern/particle.c$3413
https://developer.blender.org/diffusion/B/browse/master/source/blender/render/intern/source/imagetexture.c$126
However, this ibuf acquisition is prevented by the
R.r.scemode & R_NO_IMAGE_LOAD
flag. This flag is used to prevent the icon render job from loading large texture files. It is only set by that job'sstart
method:https://developer.blender.org/diffusion/B/browse/master/source/blender/editors/render/render_preview.c$721
What appears to be happening is a kind of thread race between icon render and scene update jobs after loading a blend file: The first hair system usually loads fine, because it manages to acquire ibufs before the icon job kicks in. Then however, if the 1st psys takes some time to create paths, the icon render sets this scene flag, thus preventing any later psys eval from lazy-loading it's textures. The only way to then get correct hair paths is to force image loading some other way (open in image editor, force reload, etc) and kick the psys.
Effectively the icon rendering totally disables all lazy ibuf loading! It makes sense to not load large textures during icon rendering (this was the reason for introduction of the flag), but because it uses a persistent scene flag for this it interferes with all other users of textures ... I suppose the flag should be some kind of localized job context setting, rather than abusing the scene's
RenderData
flags for the purpose.Changed status to: 'Open'
Added subscriber: @Sergey
@Sergey Here is a bad tentative fix for the issue:
Certainly this is not the way to do it, just shows how forcibly loading ibufs avoids the issue ...
This issue was referenced by
d9c77a490c
Changed status from 'Open' to: 'Resolved'
Closed by commit
d9c77a490c
.