Regression: Rendering hair instances size in animation bug with animated emitter object scale #97625

New Issue

Denis Belov · 2022-04-26T14:40:28+02:00

Denis Belov commented

2022-04-26 14:40:28 +02:00

System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 472.47

Blender Version
Broken: version: 3.1.2, branch: master, commit date: 2022-03-31 17:40, hash: cc66d1020c
Broken: 2.93
Worked: 2.92

Regression from 50782df425.

Short description of error
Incorrect rendered instanced object scale if rendering hair animation with animated object.

Exact steps for others to reproduce the error
1 Create Cube and object for instancing
2 Set cube scale animation for some frame range
3 Apply patricle system to cube (hair / rendered instances as object or collection)
4 Try to render single frame and render animation, compare difference

hair_render.mp4
test_hair.blend

Will set to high prio to raise awareness this is a regression, but this can probably be lowered again since also involves the EOL particle system.
Note: if you really need to render this, consider using Cycles (where this still works when the Persistent Data option is OFF.

**System Information** Operating system: Windows-10-10.0.19044-SP0 64 Bits Graphics card: NVIDIA GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 472.47 **Blender Version** Broken: version: 3.1.2, branch: master, commit date: 2022-03-31 17:40, hash: `cc66d1020c` Broken: 2.93 Worked: 2.92 Regression from 50782df425. **Short description of error** Incorrect rendered instanced object scale if rendering hair animation with animated object. **Exact steps for others to reproduce the error** 1 Create Cube and object for instancing 2 Set cube scale animation for some frame range 3 Apply patricle system to cube (hair / rendered instances as object or collection) 4 Try to render single frame and render animation, compare difference [hair_render.mp4](https://archive.blender.org/developer/F13029909/hair_render.mp4) [test_hair.blend](https://archive.blender.org/developer/F13029910/test_hair.blend) Will set to high prio to raise awareness this is a regression, but this can probably be lowered again since also involves the EOL particle system. Note: if you really need to render this, consider using Cycles (where this still works when the `Persistent Data` option is OFF.

Denis Belov commented

2022-04-26 14:40:28 +02:00

Added subscriber: @DenisBelov

Philipp Oeser changed title from ~~Rrendering hair animation bug with animated object~~ to Rendering hair animation bug with animated emitter object scale

2022-04-26 15:07:16 +02:00

Philipp Oeser commented

2022-04-26 15:26:39 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2022-04-26 15:26:39 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Philipp Oeser commented

2022-04-26 15:26:39 +02:00

Seems like 2.83 did not take object scale animated into account at all (so not all frames dont match there either?)?
Seems like 2.93 does this, so I assume there was some bugfix in between regarding animation rendering, not sure yet why [even though animated object scale is now properly taken into account] instance sizes dont match between viewport and render and why single render is wrong

@DenisBelov : what makes you think 2.83 was better here?

Seems like 2.83 did not take object scale animated into account at all (so not all frames dont match there either?)? Seems like 2.93 does this, so I assume there was some bugfix in between regarding animation rendering, not sure yet why [even though animated object scale is now properly taken into account] instance sizes dont match between viewport and render and why single render is wrong @DenisBelov : what makes you think 2.83 was better here?

Denis Belov commented

2022-04-26 15:46:19 +02:00

In 2.83 we can scale hair particles with object, for example object with "drops" on it, and now "drops" are rendering at full scale even if object scale is zero and do not scale proportionaly with main object. Plus viewport still shows old behaviour. I i showed this behaviour in attached video.

Philipp Oeser commented

2022-04-26 16:10:17 +02:00

Changed status from 'Needs User Info' to: 'Needs Triage'

Philipp Oeser commented

2022-04-26 16:10:17 +02:00

Need to look at his again with fresh eyes later....
Object Scale seems to be broken? https://docs.blender.org/manual/en/3.2/physics/particles/emitter/render.html#object

Need to look at his again with fresh eyes later.... `Object Scale` seems to be broken? https://docs.blender.org/manual/en/3.2/physics/particles/emitter/render.html#object

Philipp Oeser commented

2022-05-06 14:24:38 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Philipp Oeser commented

2022-05-06 14:24:38 +02:00

Added subscriber: @brecht

Philipp Oeser commented

2022-05-06 14:24:38 +02:00

Regression from 50782df425.

Will set to high prio to raise awareness this is a regression, but this can probably be lowered again since also involves the EOL particle system.
Note: if you really need to render this, consider using Cycles (where this still works when the Persistent Data option is OFF.

CC @brecht

Regression from 50782df425. Will set to high prio to raise awareness this is a regression, but this can probably be lowered again since also involves the EOL particle system. Note: if you really need to render this, consider using Cycles (where this still works when the `Persistent Data` option is OFF. CC @brecht

Philipp Oeser changed title from ~~Rendering hair animation bug with animated emitter object scale~~ to Regression: Rendering hair instances size in animation bug with animated emitter object scale

2022-05-06 14:25:48 +02:00

Brecht Van Lommel commented

2022-05-10 18:48:11 +02:00

The issue here is in the depsgraph / particles. The viewport does not update correctly either, and persistent data relies on the same mechanism.

Particles make particle size independent of object scale, by scaling down the particles so that it cancels out with the object scale. I think that's a mistake in the design, particles should scale with the object transform just like meshes. Geometry nodes, point clouds and instances get this right.

The problem is that trying to fix this would lead to performance regressions for the most common case where scale is not animated, and transforming an object should not recompute the particles. Unless we make deep changes to the particle evaluation, which is not going to happen anymore.

The issue here is in the depsgraph / particles. The viewport does not update correctly either, and persistent data relies on the same mechanism. Particles make particle size independent of object scale, by scaling down the particles so that it cancels out with the object scale. I think that's a mistake in the design, particles should scale with the object transform just like meshes. Geometry nodes, point clouds and instances get this right. The problem is that trying to fix this would lead to performance regressions for the most common case where scale is not animated, and transforming an object should not recompute the particles. Unless we make deep changes to the particle evaluation, which is not going to happen anymore.

Philipp Oeser removed the

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Regression: Rendering hair instances size in animation bug with animated emitter object scale #97625