WebGLRenderer, KTX2Loader: Support R11G11B10

[donmccurdy]

Related issues:

• KTX2Loader: Support RGB9E5 #31611
• WebGLRenderer: Add support for WEBGL_render_shared_exponent. #27992
• Use WEBGL_render_shared_exponent for HDR textures #27971
• Feature: HDR cubemap from a single file #9688

Description

Adds support to KTX2Loader for textures using the R11G11B10 format. Colors in the KTX2 sample are slightly different (#4dae4b vs. #4eaf4a) but this is expected as the format has less precision in the 0–1 range: https://bartwronski.com/2017/04/02/small-float-formats-r11g11b10f-precision/.

To create the sample included in this PR, I used KTX Software:

ktx create --format B10G11R11_UFLOAT_PACK32 --assign-oetf linear --assign-primaries bt709 --generate-mipmap source/r11g11b10.exr ktx2/2d_r11g11b10_linear.ktx2

See: donmccurdy/KTX2-Samples@6248251

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.74 79.06	338.9 79.1	+163 B +43 B
WebGPU	568.78 157.23	568.98 157.28	+197 B +44 B
WebGPU Nodes	567.39 156.99	567.59 157.03	+197 B +42 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	470.52 113.83	470.64 113.87	+124 B +41 B
WebGPU	642.52 173.77	642.68 173.81	+158 B +42 B
WebGPU Nodes	597.17 163.07	597.33 163.09	+158 B +21 B

[donmccurdy]

Note - I've included the same changes in WebGPURenderer, because it looked easy enough to allow. But I get (unrelated) errors when trying to swap in WebGPURenderer on this KTX2 example, so I haven't confirmed whether R11G11B10 works for WebGPURenderer or not.

[Mugen87]

We can still merge the PR and then check the errors with the WebGPU backend.