WebGPURenderer: enable better WebXR depth sensing

[cabanier]

Description

The current WebXR depth sensing implementation simply copies the depth into the target buffer.
This has the drawback of not being able to use the latest WebXR additions which make the depth "stick" to the real world.
In addition, we can't blur with the occlusion pixels.

Solution

I'd like to enhance the WebGPURenderer with a custom shader that always runs first.
In it, we will do the reprojection of the depth pixels as well as the blurring similar to the example of the WebXR samples.

@Mugen87 Is there a way to enhance the renderer to always to an operation first? I noticed that fog always runs last.

Alternatives

We could implement what was done in the old render but the occlusion is not good that way

Additional context

No response

[sunag]

@cabanier I'd like to know more about the proposal. What you would need to modify even if the operation is executed first. Are you thinking of overwriting the depth of the material with a custom shader?

[cabanier]

@cabanier I'd like to know more about the proposal. What you would need to modify even if the operation is executed first. Are you thinking of overwriting the depth of the material with a custom shader?

I was thinking of depth testing the material against the real world first and if the real world is in front of it, we would skip the remainder of the fragment code. It would be similar to the code I added in https://immersive-web.github.io/webxr-samples/layers-samples/proj-multiview-occlusion.html

[sunag]

I think we can do this with material.maskNode, its input is a bool and if it is false it will be discarded, it is executed in the first moments of the fragment stage.

[cabanier]

I think we can do this with material.maskNode, its input is a bool and if it is false it will be discarded, it is executed in the first moments of the fragment stage.

I think this would require the author to update each material that was used. The advantage of the fognode was that it was done at the scene level.

[cabanier]

I think we can do this with material.maskNode, its input is a bool and if it is false it will be discarded, it is executed in the first moments of the fragment stage.

Do you have an example that uses maskNode?