Nodes: Optional varying interpolation

[sunag]

Related issue: #24410

Description

NodeMaterial is interchangeable and uses nodes as elements to build other nodes. When you do this using varying it can generate some unnecessary varyings for the final result, for example: If you use a normalWorld, this will call normalView which also uses a varying. This generated varyings that were not used.

This update checks which shader stage varying is being used to see if interpolation is really needed, and if not, it automatically converts to a simple variable.

WebGPU

webgpu_cubemap_adjustments.html

After

// varyings
struct NodeVaryingsStruct {
	@location( 1 ) nodeVarying1 : vec2<f32>,
	@location( 2 ) nodeVarying2 : vec3<f32>,
	@location( 3 ) nodeVarying3 : vec4<f32>,
	@location( 4 ) nodeVarying4 : vec3<f32>,
	@location( 6 ) nodeVarying6 : vec3<f32>,
	@location( 8 ) nodeVarying8 : vec3<f32>,
	@location( 9 ) nodeVarying9 : vec3<f32>,
	@builtin( position ) Vertex : vec4<f32>
};

// vars
var nodeVarying0 : vec3<f32>;
var nodeVarying5 : vec3<f32>;
var nodeVarying7 : vec4<f32>;
var nodeVarying10 : vec3<f32>;

Before

// varyings
struct NodeVaryingsStruct {
	@location( 0 ) nodeVarying0 : vec3<f32>,
	@location( 1 ) nodeVarying1 : vec2<f32>,
	@location( 2 ) nodeVarying2 : vec3<f32>,
	@location( 3 ) nodeVarying3 : vec4<f32>,
	@location( 4 ) nodeVarying4 : vec3<f32>,
	@location( 5 ) nodeVarying5 : vec3<f32>,
	@location( 6 ) nodeVarying6 : vec3<f32>,
	@location( 7 ) nodeVarying7 : vec4<f32>,
	@location( 8 ) nodeVarying8 : vec3<f32>,
	@location( 9 ) nodeVarying9 : vec3<f32>,
	@location( 10 ) nodeVarying10 : vec3<f32>,
	@builtin( position ) Vertex : vec4<f32>
};

// vars

WebGL

webgl_nodes_materials_standard.html

After

// varyings
varying vec2 nodeVarying0;
varying vec4 nodeVarying1;
/*varying*/ vec3 nodeVarying2;
varying vec3 nodeVarying3;
/*varying*/ vec3 nodeVarying4; 

Before

// varyings
varying vec2 nodeVarying0;
varying vec4 nodeVarying1;
varying vec3 nodeVarying2;
varying vec3 nodeVarying3;
varying vec3 nodeVarying4; 

This contribution is funded by Google

[LeviPesin]

Maybe use sets for vars?

[sunag]

I think it's better to work with indexing in vars, since that sets would only be for a specific case.