WebGPURenderer: Ensure render targets have consistent default depth values.

[Mugen87]

Related issue: -

Description

This issue has driven me nuts^^. I've encountered a strange rendering issue in a complex render setup and couldn't find the root cause. It took a while to isolate this issue but the following test case demonstrates a bug in WebGPURenderer:

https://jsfiddle.net/2mdwzyge/

As you can see nothing is rendered but when switching to the WebGL 2 backend the result is as expected (a rotating cube producing trails).

When autoClear is set to false, the default values in a depth texture actually vary between WebGPU and WebGL (0 vs 1). This can produce hard to track bugs/inconsistent behavior so we should make sure WebGPURenderer setups depth textures with consistent default depth values.

The PR is doing this by checking for uninitialized render targets and clears the depth once if autoClear or autoClearDepth is disabled. When the auto clear flags are not changed, the render target will be guaranteed in a valid state because of the automatic clear.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	359.97 85.54	359.97 85.54	+0 B +0 B
WebGPU	631.1 175.11	631.35 175.18	+252 B +69 B
WebGPU Nodes	629.21 174.83	629.47 174.9	+252 B +70 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	492.17 120.12	492.17 120.12	+0 B +0 B
WebGPU	703.53 189.96	703.78 190.02	+252 B +68 B
WebGPU Nodes	652.75 177.35	653 177.41	+252 B +68 B

[Mugen87]

Something with the framebuffer setup/clear in the WebGL backend isn't right. Investigating...

[Mugen87]

This was actually a bug. Nested calls of clear() corrupted the render context. It's not a common use case but the new clearDepth() call exposed it.

The callDepth approach introduced in #32546 for managing render contexts isn't ideal, tbh. While it helps to reduce the overall number of render contexts, it is error prone since you have to be careful not to request the wrong context like clear() did.