WebGLRenderer: Don't support double-sided, transmissive objects with WEBGL_multisampled_render_to_texture.

[Mugen87]

Related issue: #28131

Description

The renderer supports double-sided, transmissive objects only with multisampled transmissive render targets. That's because the transmissive render target is used as source and target which normally would produce a feedback loop. The loop isn't "visible" because multisampled render targets use more than one framebuffer.

This assumption is not true when the WEBGL_multisampled_render_to_texture extension is available since it enables multisampling support without an explicit resolve. This currently means double-sided, transmissive objects show no inner reflections with the Quest browser and produce a WebGL warning in the browser console.

Until a solution is available (see #28131 (comment)), I suggest to exclude double-sided, transmissive objects in renderTransmissionPass() when WEBGL_multisampled_render_to_texture is available. This avoids the WebGL warning and improves the performance.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
674.4 kB (167.1 kB)	674.4 kB (167.1 kB)	+55 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
453.8 kB (109.5 kB)	453.8 kB (109.6 kB)	+56 B