WebGPURenderer: Optimize and reuse varyings

[RenaudRohlinger]

WebGPU is currently limited to 16 varyings, which can be quickly exceeded with the node system, leading to errors such as:

This PR sets up the naming of varyings where possible in order to reuse them, thereby enhancing performance and enabling debugging.

Before this PR with a fairly advanced setup:

After this PR, on the same program:

The only issue I encountered while working on this was my inability to assign the v_normalLocal name to normalLocal. /cc @sunag. Otherwise, everything seems to function well, even in complex setups.

This contribution is funded by Utsubo

[RenaudRohlinger]

Seems like some varyings have some specific issue with the WebGLBackend on 4 examples. Probably flat identifier and hardcoded GLSLNodeBuilder details. Will check tomorrow.

[sunag]

Hmm... Node.getHash() and Node.getShared() should work in this sense. I think it's worth checking out too because it's not sharing.

[RenaudRohlinger]

Somehow isolated one of the issue, basically using nodes will just always create new varying even when not necessary. For example using TBNViewMatrix will create a new unnecessary varying instead of grouping them in the vertex.

This will generate 3 varyings:

export const TBNViewMatrix = mat3( tangentView, bitangentView, normalView );
--> bitangentView is an independent varying of normalView.cross( tangentView )

Doing this will use only 2 varyings:

export const TBNViewMatrix = mat3( tangentView, normalView.cross( tangentView ), normalView );

We would need a system to automatically pack the varyings I guess? Seems like my PR is helping when providing names to all varyings. /cc @sunag

[sunag]

I will check, the current system should resolve this kind of issue, maybe has some bug related with cache. Your PR is good because give name for varyings, the names should help in debugging but should not be essential for optimization until fix this issue.

[RenaudRohlinger]

@sunag One of the issue with the current node system when using named varying is that the AssignNode seems to conflict with the VaryingNode (Only for WebGPU). WGLSL is generating varyings.v_normal but tries to use v_normal.

Error:

Which is ok and runs well with the GLSLNodeBuilder:

To reproduce simply add names to the varyings of the NormalNode and such and try for example to run webgpu_backdrop_water

I don't think I will be able to resolve this easily as my knowledge on the node system is still a bit limited but I believe this issue will need to be resolve first in order to convert this draft to a PR a add various names for the attributes and varyings.

[sunag]

@RenaudRohlinger Could you share your test again? I pushed a commit for us to analyze. Just NormalNode yet.

[RenaudRohlinger]

This code doesn't seem to work if you try webgpu_backdrop_water