TSL: Introduce instance() for custom use

[sunag]

Related issue: #29071

Description

Introduce instance() for custom use.

mesh = new THREE.Mesh( geometry, material );
mesh.count = count;

instanceMatrix = new THREE.InstancedBufferAttribute( new Float32Array( count * 16 ), 16 );
instanceMatrix.setUsage( THREE.DynamicDrawUsage );

mesh.material.positionNode = Fn( ( { object } ) => {

	// object is the mesh here
	// .append() will run instance() immediately, appying instanceMatrix transform in positionLocal and normalLocal
	// this way you can get positionLocal before or after instance(()
	instance( object.count, instanceMatrix ).append();

	return positionLocal;

} )();

scene.add( mesh );

// update matrix

dummy.matrix.toArray( instanceMatrix.array, i ++ * 16 );

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	339.37 79.06	339.37 79.06	+0 B +0 B
WebGPU	478.22 132.63	478.37 132.7	+153 B +64 B
WebGPU Nodes	477.68 132.51	477.84 132.58	+153 B +69 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	464.82 112.02	464.82 112.02	+0 B +0 B
WebGPU	546.95 148.2	547.04 148.23	+93 B +34 B
WebGPU Nodes	502.83 137.91	502.93 137.95	+93 B +48 B