d3f84449ad
Add a "dumb vector" storage option for custom normals, with the "custom_normal" attribute. Adjust the mesh normals caching to provide this attribute if it's available, and add a geometry node to store custom normals. ## Free Normals They're called "free" in the sense that they're just direction vectors in the object's local space, rather than the existing "smooth corner fan space" storage. They're also "free" in that they make further normals calculation very inexpensive, since we just use the custom normals instead. That's a big improvement from the existing custom normals storage, which usually significantly decreases viewport performance. For example, in a simple test file just storing the vertex normals on a UV sphere, using free normals gives 25 times better playback performance and 10% lower memory usage. Free normals are adjusted when applying a transformation to the entire mesh or when realizing instances, but in general they're not updated for vertex deformations. ## Set Mesh Normal Node The new geometry node allows storing free custom normals as well as the existing corner fan space normals. When free normals are chosen, free normals can be stored on vertices, faces, or face corners. Using the face corner domain is necessary to bake existing mixed sharp and smooth edges into the custom normal vectors. The node also has a mode for storing edge and mesh sharpness, meant as a "soft" replacement to the "Set Shade Smooth" node that's a bit more convenient. ## Normal Input Node The normal node outputs free custom normals mixed to whatever domain is requested. A "true normal" output that ignores custom normals and sharpness is added as well. Across Blender, custom normals are generally accessed via face and vertex normals, when "true normals" are not requested explicitly. In many cases that means they are mixed from the face corner domain. ## Future Work 1. There are many places where propagation of free normals could be improved. They should probably be normalized after mixing, and it may be useful to not just use 0 vectors for new elements. To keep the scope of this change smaller, that sort of thing generally isn't handled here. Searching `CD_NORMAL` gives a hint of where better propagation could be useful. 2. Free normals are displayed properly in edit mode, but the existing custom normal editing operators don't work with free normals yet. This will hopefully be fairly straightforward since custom normals are usually converted to `float3` for editing anyway. Edit mode changes aren't included here because they're unnecessary for the procedural custom normals use cases. 3. Most importers can probably switch to using free normals instead, or at least provide an option for it. That will give a significant import performance improvement, and an improvement of Blender's FPS for imported scenes too. Pull Request: https://projects.blender.org/blender/blender/pulls/132583
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