TSL: varyingProperty

[sunag]

Related issue: #26704

Description

varyingProperty declares varying without having to set an initial value as in varying, thus saving GPU resources.

This was used in some specific cases, such as Line2NodeMaterial and can now be used directly in WGSL if necessary.

const myVarying = varyingProperty( 'vec3', 'myVarying' );

const positionTransformFn = wgslFn( `
	fn positionTransformFn( position: vec3<f32> ) -> vec3<f32> {

		// varyings.* is the structure that will store all the varyings
		// you can use it to access/store your varying value

		varyings.myVarying = position;

		return position;

	}
`, [ myVarying ] );

material = new MeshBasicNodeMaterial();
material.colorNode = myVarying;
material.positionNode = positionTransformFn( { position: positionLocal } );

[sunag]

/cc @Spiri0