WebGPU Fn second parameter

[ljamesjr85]

Description

I was looking at your webgpu skinning example and noticed a second argument ('void') passed to the Fn exported from 'three/tsl'.

At first I thought maybe it wasn't used. But, it seems like an undocumented part of what the function can take and when I replicated the example for my own use case it only seemed to work then that argument was included specifically as 'void' (see "updatedSkinningPoints")

Reproduction steps

This is used in the example below:
https://github.com/mrdoob/three.js/blob/master/examples/webgpu_skinning_points.html

Code

const updateSkinningPoints = Fn( () => {

								const pointPosition = pointPositionArray.element( instanceIndex );
								const pointSpeed = pointSpeedArray.element( instanceIndex );

								const skinningWorldPosition = objectWorldMatrix( child ).mul( skinningPosition );

								const skinningSpeed = skinningWorldPosition.sub( pointPosition );

								pointSpeed.assign( skinningSpeed );
								pointPosition.assign( skinningWorldPosition );

							}, 'void' );

							materialPoints.positionNode = Fn( () => {

								updateSkinningPoints();

								return pointPositionArray.toAttribute();

							} )().compute( countOfPoints ).onInit( () => {

								// initialize point positions and speeds

								renderer.compute( updateSkinningPoints().compute( countOfPoints ) );

							} );

Live example

https://github.com/mrdoob/three.js/blob/master/examples/webgpu_skinning_points.html

Screenshots

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Version

Version In Example

Device

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Browser

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OS

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[DennisSmolek]

Pretty sure thats the Node Layout.

Some tells the builder what goes in/out of the Fn

[Mugen87]

Indeed, it's the layout. void is a valid node type which means the first Fn() definition has no return node value.

Normally, the type can be derived from the node that is returned by a function so the layout parameter is not mandatory. But if the return statement is missing like in updateSkinningPoints(), you must add void right now so it's clear for the node system that there is no return value.

layout is not necessarily just a string defining the return node type. It can be an object if you want to define the types for parameters and the return value:

three.js/src/nodes/display/BlendModes.js

Line 172 in 169d4e1

}, { color: 'vec4', return: 'vec4' } );

I've updated the Wiki and added the layout parameter for Fn .