Examples: Add WebGPU KTX2 test demo.

[Mugen87]

Related issue: #31690

Description

The PR adds webgl_loader_texture_ktx2 as webgpu_loader_texture_ktx2 so it's easier to test KTX2 textures with WebGPURenderer.

The example also demonstrates the differences between viewport/scissor handling to WebGLRenderer. WebGPU does not allow negative viewport values so the textures views can only be rendered when their are full in view.

[Mugen87]

@donmccurdy I'll add TODOs here for #31690 (comment).

[hybridherbst]

Thanks for adding this!

WebGPU does not allow negative viewport values so the textures views can only be rendered when their are full in view.

That's a visually jarring change. Shouldn't the viewport/scissor values be clamped to the window instead, so that the visual result stays the same?

[hybridherbst]

It's great that so many formats already work again in WebGPU now!

Maybe you can add this test file (which works in WebGL but doesn't yet in WebGPU) as well:
https://github.com/mrdoob/three.js/blob/c3ad482124c441f591ffe67a02e70c7aa5374bc3/examples/textures/ktx2/2d_uastc_hdr4x4.ktx2 (from #31689)

[Mugen87]

That's a visually jarring change. Shouldn't the viewport/scissor values be clamped to the window instead, so that the visual result stays the same?

I must focus on other things right now so I would appreciate if you could give it a try. Otherwise I'll revisit this later.

[Mugen87]

Maybe you can add this test file (which works in WebGL but doesn't yet in WebGPU) as well:

We can do that when #31689 is merged 👍 .