Add depth testing for compute GSplat renderer when CameraFrame depth prepass is enabled

[mvaligursky]

Enable the compute-based Gaussian Splat rasterizer to depth-test against opaque scene geometry using the linear depth texture from the depth prepass.

Changes:

• Add a DEPTH_TEST shader variant to the compute rasterize shader that loads per-pixel scene depth and skips splats behind opaque geometry
• Early-out optimization: when all four pixels in a 2x2 quad are behind scene depth, skip remaining splats (front-to-back ordering)
• Extend GSplatLocalDispatchSet variant system to support color-depth variant with sceneDepthMap binding
• Detect depth availability at dispatch time via camera.shaderParams.sceneDepthMapLinear and uSceneDepthMap
• Set requiresDepth: true on the beforePasses entry to signal depth prepass dependency
• Vectorize transmittance early-out using all() for consistency
• Deduplicate transmittance declarations across pick/color branches
• Refactor getRasterizeCompute to accept boolean parameters instead of string keys

Examples:

• Updated lod-streaming example with an "Occluder" toggle in Scene controls that shows an orange cube and enables the depth prepass

Performance:

• Depth-occluded tiles early-out immediately, avoiding unnecessary splat evaluation behind opaque geometry

[Copilot]

Pull request overview

This PR adds an optional depth-test path to the compute-based Gaussian Splat (GSplat) local rasterizer so splats can be occluded by opaque scene geometry when a linear-depth prepass is enabled (e.g., via CameraFrame.rendering.sceneDepthMap).

Changes:

• Adds a DEPTH_TEST WGSL shader variant that loads the scene’s linear depth texture and skips splats behind it, including an early-out when a splat is behind all 2x2 quad samples.
• Extends GSplatLocalDispatchSet rasterize variants to support a color-depth pipeline with a sceneDepthMap binding and refactors variant selection to use boolean flags.
• Updates the lod-streaming example UI to toggle an occluder cube and enable/disable the depth prepass.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/scene/shader-lib/wgsl/chunks/gsplat/compute-gsplat-local-rasterize.js	Adds DEPTH_TEST sampling/comparisons against linear scene depth during compute rasterization.
src/scene/gsplat-unified/gsplat-local-dispatch-set.js	Adds bind-group support + shader defines for the depth-test rasterize variant.
src/scene/gsplat-unified/gsplat-compute-local-renderer.js	Selects depth-test variant at dispatch time and marks the pass as requiresDepth.
examples/src/examples/gaussian-splatting/lod-streaming.example.mjs	Adds an occluder entity and toggles CameraFrame depth prepass via UI state.
examples/src/examples/gaussian-splatting/lod-streaming.controls.mjs	Adds an “Occluder” toggle control.

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[Copilot]

requiresDepth on camera.beforePasses doesn’t appear to be consumed anywhere in the current codebase (no reads found), so setting it to true here is currently a no-op and the added comment implies behavior that doesn’t actually happen. Either wire requiresDepth into the scheduling logic (so it actually triggers/requests a depth prepass) or keep this metadata/comment aligned with what the engine does today.

Suggested change

	// requiresDepth hints that a depth prepass should run first, so the
	// rasterize shader can skip splats behind opaque geometry.
	camera.beforePasses.push({ pass: this.framePass, requiresDepth: true });
	camera.beforePasses.push({ pass: this.framePass });