docs: Volumetric Global Illumination (Radiance Cascade) example

[aleksanderkatan]

I have trouble optimizing this.
It may be due to the fact that we call castInterval upwards of 14 billion times a frame (given a resolution of 1000x1000).

I tried to optimize this by prerendering the sdfs into a texture so that each pixel averages only one getScene call but it didn't help much. I also added a slider that reduces the resolution of the canvas.

I still don't get the radiance cascade algorithm, but I'm starting to suspect that it isn't implemented correctly (either the OG example, or a mistake in the port).
I suggest that we leave this as a DEV example, and try to optimize this later.

Some links:

• original example,
• short overview of the technique,
• paper.

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Pull request overview

This PR adds a new volumetric radiance cascades example to the rendering category, implementing a port of the "2D Volumetric Radiance Cascades" shader from Shadertoy. The example demonstrates an advanced global illumination technique using radiance cascades to compute volumetric lighting in 2D with fully converged (noise-free) radiance. The implementation includes scene rendering with signed distance functions, the core radiance cascade algorithm with bilinear interpolation, and post-processing with ACES tonemapping and gamma correction.

Key changes:

• Adds complete volumetric radiance cascades implementation with configurable cascades, quality settings, and multiple demo scenes (Shadertoy, Hearts, Dots)
• Introduces mockMathRandom() utility for deterministic testing of examples using randomness
• Includes comprehensive test coverage with inline shader snapshot validation

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/typegpu/tests/examples/utils/commonMocks.ts	Adds mockMathRandom() helper to ensure deterministic test behavior for examples using random values
packages/typegpu/tests/examples/individual/volumetric-radiance-cascades.test.ts	Complete test suite with shader code snapshot validation for the new example
apps/typegpu-docs/src/examples/rendering/volumetric-radiance-cascades/meta.json	Example metadata configuration marking it as experimental with relevant tags
apps/typegpu-docs/src/examples/rendering/volumetric-radiance-cascades/index.ts	Main entry point orchestrating the three-pipeline rendering system (prerender, cascade merge, display)
apps/typegpu-docs/src/examples/rendering/volumetric-radiance-cascades/index.html	HTML template with attribution to the original Shadertoy implementation
apps/typegpu-docs/src/examples/rendering/volumetric-radiance-cascades/castAndMerge.ts	Core radiance cascades algorithm with extensive documentation and bilinear interpolation
apps/typegpu-docs/src/examples/rendering/volumetric-radiance-cascades/scenes.ts	Scene definitions using SDFs (circles, hearts) with animated elements
apps/typegpu-docs/src/examples/rendering/volumetric-radiance-cascades/image.ts	Post-processing functions for ACES tonemapping and sRGB gamma correction

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