WebGLRenderer: Allow overrideMaterial to be changed on a per-object b…

[fleroviux]

Description

Right now when rendering a scene its override material will only be read once at the start of renderObjects(), which means that it cannot be changed e.g. in onBeforeRender() on a per-render-object basis. But for our G-buffer implementation we wanted to be able to pick an override material based on mesh/material variables like morphTargets/morphNormals or skinning which would be a bit expensive to enable for all render objects.

This patch moves the override material logic into the renderObject() method, after the call to onBeforeRender(), which faciliated us to do this. As a side effect onBeforeRender() now receives the original mesh material as parameter instead of the override material, which is desirable in my opinion.

[Mugen87]

The skinning property will be gone with r129, see #21788.

Assuming there would be no morphTargets and morphNormals property, would you still need this PR?

[fleroviux]

WebGLPrograms would then automatically add flags for skinning and morph targets to the program and its key right?
But that probably wouldn't work for RawShaderMaterial, which we use to render into multiple render targets and is still necessary with the merged MRT feature ( see #16390 (comment) ).

So replacing morphTargets with something like MorphMesh would work if there is a solution for RawShaderMaterial to be automatically compiled into different programs based on the mesh or for MRT to work with a normal ShaderMaterial.

Please correct me if I have any misconceptions.

[Mugen87]

The idea is not to introduce new class like MorphMesh but to detect whether morph targets are defined in the geometry or not. The renderer is then able to produce different programs even for a single material that is used for a normal and animated mesh.

[fleroviux]

I looked at the PR #21788 and noticed that WebGLShadowMap already achieves something similar to what we want to do with renderBufferDirect(), I didn't know about that method before. Might actually make for an overall cleaner solution than using overrideMaterial and onBeforeRender, but I have to evaluate that. If that works for us then this PR wouldn't be necessary anymore.

[Mugen87]

With r131, morphTargets/morphNormals have been removed. That means you can use the same override material for correctly processing animating meshes.

I looked at the PR #21788 and noticed that WebGLShadowMap already achieves something similar to what we want to do with renderBufferDirect(), I didn't know about that method before.

Also noticed that with r131 the WebGLShadowMap class does not need the former materials variants logic anymore. So a single set of depth materials is sufficient for processing the scene. Previously, it was necessary to have separate depth materials for skinned and morphed meshes. Custom implementations also benefit from this simplification.

Ideally, it's now not necessary anymore to modify renderObjects() with this PR.

[fleroviux]

Thank you! I'll make sure to try this once we update.