PMREM envMap bad performance

Recently I’ve been migrating my app from normal cubemap to PMREM and noticing 3-5x drop in performance (it was 50fps, but now is just 11fps using PMREM).

After looking around in the source code to find out the difference, I see in fragment shader, function textureCubeUV has 1 to 2 calls to bilinearCubeUV, each call will access the envMap 4 times: https://github.com/mrdoob/three.js/blob/c1ea11e4ff7aaa41334cd8d2154a5cd55b94b641/src/renderers/shaders/ShaderChunk/cube_uv_reflection_fragment.glsl.js#L118 So each pixel will access envMap texture 4 or 8 times per frame? I guess this is where the performance drop come from.

Could the PMREM code can be improved somehow to achieve better performance?

[elalish]

@Ben-Mack 100s of different materials? The draw call overhead alone could be a bigger problem. Is there no way to combine them with texture atlasing? In any case, if you can share an example we can test with/without PMREM then we’ll have a much better chance of improving the performance.

[WestLangley]

The renderer internally converts environment maps automatically to PMREMs

…except for CubeCamera.renderTarget. See #22236.