[InstancedUniformsMesh] Does .setUniformAt() erase material.onBeforeCompile?

I created a ShaderMaterial with some custom Matrix4 uniforms, to rotate geometry on the vertex shader. This works when used on InstancedMesh and even InstancedUniformsMesh.

But once I invoke .setUniformAt() to bind per-instance uniforms, those material-bound uniforms no longer work-- those rotation matrices no longer rotate anything, which leads me to suspect that they fell back to identity matrices (mat4(1.0)) when the shader couldn’t access the uniform anymore.

[peterqliu]

I was also able to sidestep it by calling onBeforeCompile after setUniformAt, but agree that fixing this would better match expectations and get the small perf boost.

[lojjic]

Aha! Yup, I see the problem. When the set of instanced uniforms changes, I currently create a new derived material instance. That will carry over any onBeforeCompile from the base material, but not any that was assigned to the previous derived material.

In your testcase, if you assign material.onBeforeCompile instead of cube.material.onBeforeCompile, it’ll work.

But, I should be able to reuse the derived material when the instanced uniforms change rather than instantiating a new one, which would fix the unexpected behavior in addition to being slightly more performant.