Support for USD PointInstancer #96747
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Reference: blender/blender#96747
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System Information
Operating system: Win10
Graphics card: GTX 1660 Ti
Blender Version
Broken: 3.1
Short description of error
After loading a USD file with type particleInstancer attached with spheres as child, Blender failed to draw the points as spheres. Instead, the displayed object in the layout window is just a singular point at the origin. Example file attached.example_sim_granular.zip
Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).
Added subscriber: @anthropoy
Added subscribers: @makowalski, @dr.sybren, @lichtwerk
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
@makowalski : havent gotten to building USD to get access to utils that let me examine a.usd the same way I can examine an alembic .abc (so I cannot really tell how the USD looks from the inside), but I assume this is not implemented yet?
For me, a single empty is imported here (under another empty for the particle system under another empty as the root).
Also not sure if the plans are to do it like alembic in blender [which imports verts with meshsequence cache modifier for plain particles or objects with transform caches for instanced particles afaict], or if this will somehow end up on the pointcloud type?
CC @dr.sybren
Hello @lichtwerk. In this case, the USD contains a PointInstancer. Indeed, this hasn't been implemented yet. (In the
universal-scene-description
branch there is support for importing scene instances but not point instances.) I am leaning towards importing PointInstancers into Blender as particle systems with particles represented as meshes. But this is open to discussion, of course, and we could potentially provide more than one option. Regardless, supporting point instancing is an important feature I was planning to add.Hi @makowalski, it would be great to have the option that the PointInstancers be imported as particle systems and the particles to be represented by the "child" attached to the PointInstancers.
Thank you for the feedback @anthropoy. I am investigating this option and will post progress in this task.
Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'
Error loading USD file with point typeto Support for USD PointInstancerAdded subscriber: @HooglyBoogly
Since the old particle system is deprecated, I don't think this is the right approach. Without more knowledge of USD I'm not sure what to suggest instead, but I would think something using the same type of instances generated by geometry nodes would be preferable (see
InstancesComponent
). That has support for arbitrary generic attributes on instances.Thanks @HooglyBoogly! I'll investigate your suggestion.
I'm guessing here a bit, but one approach would be creating a point cloud with a geometry nodes modifier that uses the
Instance on Points
node. All of the instances could go in a collection, and the point cloud could have aninstance_index
attribute used to choose the correct instance.Yes, that sounds like a promising approach!
Added subscriber: @zNight
I've started hacking out support for point instancers here: https://projects.blender.org/blender/blender/compare/universal-scene-description...expenses/blender:usd-read-pointinstancer.
Things seems fairly straightforward so far, with two exceptions:
stage.GetPrototypes()
doesn't return prototypes for point instancers currently, so these have to be fetched via a different method.I'm happy to continue with the branch and to try and get it merged in, but I think I need some advice on these two aspects.
Additionally, here's what I imagine the geometry node setup to look like. No surprises really, just a question of what to do about rotations.
The "Instance on Points" node doesn't have a rotation socket input yet, but geometry nodes does support the rotation (quaternion) data type. You can use a "Rotation to Euler" node to connect a quaternion attribute to the node.
@HooglyBoogly Oh, you're right! The changes that add that type haven't made it over to the
universal-scene-description
branch yet.