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							<html lang="en">
<head>
	<title>three.js webgpu - compute cloth</title>
	<meta charset="utf-8">
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<body>

<div id="info">
	<a href="https://threejs.org" target="_blank" rel="noopener">three.js</a> webgpu - compute cloth<br/>
	Simple cloth simulation with a verlet system running in compute shaders
</div>

<script type="importmap">
	{
		"imports": {
			"three": "../build/three.webgpu.js",
			"three/webgpu": "../build/three.webgpu.js",
			"three/tsl": "../build/three.tsl.js",
			"three/addons/": "./jsm/"
		}
	}
</script>

<script type="module">

	import * as THREE from 'three';

	import { Fn, If, Return, instancedArray, instanceIndex, uniform, select, attribute, uint, Loop, float, transformNormalToView, cross, triNoise3D, time } from 'three/tsl';

	import { GUI } from 'three/addons/libs/lil-gui.module.min.js';
	import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
	import { RGBELoader } from 'three/addons/loaders/RGBELoader.js';

	let renderer, scene, camera, controls;

	const clothWidth = 1;
	const clothHeight = 1;
	const clothNumSegmentsX = 30;
	const clothNumSegmentsY = 30;
	const sphereRadius = 0.15;

	let vertexPositionBuffer, vertexForceBuffer, vertexParamsBuffer;
	let springVertexIdBuffer, springRestLengthBuffer, springForceBuffer;
	let springListBuffer;
	let computeSpringForces, computeVertexForces;
	let dampeningUniform, spherePositionUniform, stiffnessUniform, sphereUniform, windUniform;
	let vertexWireframeObject, springWireframeObject;
	let clothMesh, clothMaterial, sphere;
	let timeSinceLastStep = 0;
	let timestamp = 0;
	const verletVertices = [];
	const verletSprings = [];
	const verletVertexColumns = [];

	const clock = new THREE.Clock();

	const params = {
		wireframe: false,
		sphere: true,
		wind: 1.0,
	};

	init();

	async function init() {

		renderer = new THREE.WebGPURenderer( { antialias: true } );
		renderer.setPixelRatio( window.devicePixelRatio );
		renderer.setSize( window.innerWidth, window.innerHeight );
		renderer.toneMapping = THREE.ACESFilmicToneMapping;
		renderer.toneMappingExposure = 1.35;
		document.body.appendChild( renderer.domElement );

		scene = new THREE.Scene();

		camera = new THREE.PerspectiveCamera( 40, window.innerWidth / window.innerHeight, 0.01, 10 );
		camera.position.set( - 1.6, - 0.1, - 1.6 );

		controls = new OrbitControls( camera, renderer.domElement );

		controls.target.set( 0, - 0.1, 0 );
		controls.minDistance = 1;
		controls.maxDistance = 3;

		const rgbeLoader = new RGBELoader().setPath( 'textures/equirectangular/' );

		const hdrTexture = await rgbeLoader.loadAsync( 'royal_esplanade_1k.hdr' );
		hdrTexture.mapping = THREE.EquirectangularReflectionMapping;
		scene.background = hdrTexture;
		scene.backgroundBlurriness = 0.5;
		scene.environment = hdrTexture;

		setupCloth();

		const gui = new GUI();
		gui.add( stiffnessUniform, 'value', 0.1, 0.5, 0.01 ).name( 'stiffness' );
		gui.add( params, 'wireframe' );
		gui.add( params, 'sphere' );
		gui.add( params, 'wind', 0, 5, 0.1 );
		const materialFolder = gui.addFolder( 'material' );
		materialFolder.addColor( clothMaterial, 'color' );
		materialFolder.add( clothMaterial, 'roughness', 0.0, 1, 0.01 );
		materialFolder.add( clothMaterial, 'sheen', 0.0, 1, 0.01 );
		materialFolder.add( clothMaterial, 'sheenRoughness', 0.0, 1, 0.01 );
		materialFolder.addColor( clothMaterial, 'sheenColor' );

		window.addEventListener( 'resize', onWindowResize );
		controls.update();
	
		renderer.setAnimationLoop( render );

	}

	function setupVerletGeometry() {

		// this function sets up the geometry of the verlet system, a grid of vertices connected by springs

		const addVerletVertex = ( x, y, z, isFixed ) => {

			const id = verletVertices.length;
			const vertex = {
				id,
				position: new THREE.Vector3( x, y, z ),
				isFixed,
				springIds: [],
			};
			verletVertices.push( vertex );
			return vertex;

		};

		const addVerletSpring = ( vertex0, vertex1 ) => {

			const id = verletSprings.length;
			const spring = {
				id,
				vertex0,
				vertex1
			};
			vertex0.springIds.push( id );
			vertex1.springIds.push( id );
			verletSprings.push( spring );
			return spring;

		};

		// create the cloth's verlet vertices
		for ( let x = 0; x <= clothNumSegmentsX; x ++ ) {

			const column = [];
			for ( let y = 0; y <= clothNumSegmentsY; y ++ ) {

				const posX = x * ( clothWidth / clothNumSegmentsX ) - clothWidth * 0.5;
				const posZ = y * ( clothHeight / clothNumSegmentsY );
				const isFixed = ( y === 0 ) && ( ( x % 5 ) === 0 ); // make some of the top vertices' positions fixed
				const vertex = addVerletVertex( posX, clothHeight * 0.5, posZ, isFixed );
				column.push( vertex );
	
			}

			verletVertexColumns.push( column );

		}

		// create the cloth's verlet springs
		for ( let x = 0; x <= clothNumSegmentsX; x ++ ) {

			for ( let y = 0; y <= clothNumSegmentsY; y ++ ) {

				const vertex0 = verletVertexColumns[ x ][ y ];
				if ( x > 0 ) addVerletSpring( vertex0, verletVertexColumns[ x - 1 ][ y ] );
				if ( y > 0 ) addVerletSpring( vertex0, verletVertexColumns[ x ][ y - 1 ] );
				if ( x > 0 && y > 0 ) addVerletSpring( vertex0, verletVertexColumns[ x - 1 ][ y - 1 ] );
				if ( x > 0 && y < clothNumSegmentsY ) addVerletSpring( vertex0, verletVertexColumns[ x - 1 ][ y + 1 ] );

				// You can make the cloth more rigid by adding more springs between further apart vertices
				//if (x > 1) addVerletSpring(vertex0, verletVertexColumns[x - 2][y]);
				//if (y > 1) addVerletSpring(vertex0, verletVertexColumns[x][y - 2]);
	
			}
	
		}

	}

	function setupVerletVertexBuffers() {

		// setup the buffers holding the vertex data for the compute shaders

		const vertexCount = verletVertices.length;

		const springListArray = [];
		// this springListArray will hold a list of spring ids, ordered by the id of the vertex affected by that spring.
		// this is so the compute shader that accumulates the spring forces for each vertex can efficiently iterate over all springs affecting that vertex

		const vertexPositionArray = new Float32Array( vertexCount * 3 );
		const vertexParamsArray = new Uint32Array( vertexCount * 3 );
		// the params Array holds three values for each verlet vertex:
		// x: isFixed, y: springCount, z: springPointer
		// isFixed is 1 if the verlet is marked as immovable, 0 if not
		// springCount is the number of springs connected to that vertex
		// springPointer is the index of the first spring in the springListArray that is connected to that vertex

		for ( let i = 0; i < vertexCount; i ++ ) {

			const vertex = verletVertices[ i ];
			vertexPositionArray[ i * 3 ] = vertex.position.x;
			vertexPositionArray[ i * 3 + 1 ] = vertex.position.y;
			vertexPositionArray[ i * 3 + 2 ] = vertex.position.z;
			vertexParamsArray[ i * 3 ] = vertex.isFixed ? 1 : 0;
			if ( ! vertex.isFixed ) {

				vertexParamsArray[ i * 3 + 1 ] = vertex.springIds.length;
				vertexParamsArray[ i * 3 + 2 ] = springListArray.length;
				springListArray.push( ...vertex.springIds );
	
			}
	
		}

		vertexPositionBuffer = instancedArray( vertexPositionArray, 'vec3' ).setPBO( true ); // setPBO(true) is only important for the WebGL Fallback
		vertexForceBuffer = instancedArray( vertexCount, 'vec3' );
		vertexParamsBuffer = instancedArray( vertexParamsArray, 'uvec3' );

		springListBuffer = instancedArray( new Uint32Array( springListArray ), 'uint' ).setPBO( true );

	}

	function setupVerletSpringBuffers() {

		// setup the buffers holding the spring data for the compute shaders

		const springCount = verletSprings.length;

		const springVertexIdArray = new Uint32Array( springCount * 2 );
		const springRestLengthArray = new Float32Array( springCount );

		for ( let i = 0; i < springCount; i ++ ) {

			const spring = verletSprings[ i ];
			springVertexIdArray[ i * 2 ] = spring.vertex0.id;
			springVertexIdArray[ i * 2 + 1 ] = spring.vertex1.id;
			springRestLengthArray[ i ] = spring.vertex0.position.distanceTo( spring.vertex1.position );
	
		}

		springVertexIdBuffer = instancedArray( springVertexIdArray, 'uvec2' ).setPBO( true );
		springRestLengthBuffer = instancedArray( springRestLengthArray, 'float' );
		springForceBuffer = instancedArray( springCount * 3, 'vec3' ).setPBO( true );

	}

	function setupUniforms() {

		dampeningUniform = uniform( 0.99 );
		spherePositionUniform = uniform( new THREE.Vector3( 0, 0, 0 ) );
		sphereUniform = uniform( 1.0 );
		windUniform = uniform( 1.0 );
		stiffnessUniform = uniform( 0.2 );

	}

	function setupComputeShaders() {

		// This function sets up the compute shaders for the verlet simulation
		// There are two shaders that are executed for each simulation step

		const vertexCount = verletVertices.length;
		const springCount = verletSprings.length;

		// 1. computeSpringForces:
		// This shader computes a force for each spring, depending on the distance between the two vertices connected by that spring and the targeted rest length
		computeSpringForces = Fn( ()=>{

			If( instanceIndex.greaterThanEqual( uint( springCount ) ), () => {

				// compute Shaders are executed in groups of 64, so instanceIndex might be bigger than the amount of springs.
				// in that case, return.
				Return();
	
			} );

			const vertexIds = springVertexIdBuffer.element( instanceIndex );
			const restLength = springRestLengthBuffer.element( instanceIndex );

			const vertex0Position = vertexPositionBuffer.element( vertexIds.x );
			const vertex1Position = vertexPositionBuffer.element( vertexIds.y );

			const delta = vertex1Position.sub( vertex0Position ).toVar();
			const dist = delta.length().max( 0.000001 ).toVar();
			const force = dist.sub( restLength ).mul( stiffnessUniform ).mul( delta ).mul( 0.5 ).div( dist );
			springForceBuffer.element( instanceIndex ).assign( force );
	
		} )().compute( springCount );

		// 2. computeVertexForces:
		// This shader accumulates the force for each vertex.
		// First it iterates over all springs connected to this vertex and accumulates their forces.
		// Then it adds a gravital force, wind force, and the collision with the sphere.
		// In the end it adds the force to the vertex' position.
		computeVertexForces = Fn( ()=>{

			If( instanceIndex.greaterThanEqual( uint( vertexCount ) ), () => {

				// compute Shaders are executed in groups of 64, so instanceIndex might be bigger than the amount of vertices.
				// in that case, return.
				Return();
	
			} );

			const params = vertexParamsBuffer.element( instanceIndex ).toVar();
			const isFixed = params.x;
			const springCount = params.y;
			const springPointer = params.z;

			If( isFixed, () => {

				// don't need to calculate vertex forces if the vertex is set as immovable
				Return();
	
			} );

			const position = vertexPositionBuffer.element( instanceIndex ).toVar( 'vertexPosition' );
			const force = vertexForceBuffer.element( instanceIndex ).toVar( 'vertexForce' );

			force.mulAssign( dampeningUniform );

			const ptrStart = springPointer.toVar( 'ptrStart' );
			const ptrEnd = ptrStart.add( springCount ).toVar( 'ptrEnd' );

			Loop( { start: ptrStart, end: ptrEnd, type: 'uint', condition: '<' }, ( { i } )=>{

				const springId = springListBuffer.element( i ).toVar( 'springId' );
				const springForce = springForceBuffer.element( springId );
				const springVertexIds = springVertexIdBuffer.element( springId );
				const factor = select( springVertexIds.x.equal( instanceIndex ), 1.0, - 1.0 );
				force.addAssign( springForce.mul( factor ) );
	
			} );

			// gravity
			force.y.subAssign( 0.00005 );

			// wind
			const noise = triNoise3D( position, 1, time ).sub( 0.2 ).mul( 0.0001 );
			const windForce = noise.mul( windUniform );
			force.z.subAssign( windForce );

			// collision with sphere
			const deltaSphere = position.add( force ).sub( spherePositionUniform );
			const dist = deltaSphere.length();
			const sphereForce = float( sphereRadius ).sub( dist ).max( 0 ).mul( deltaSphere ).div( dist ).mul( sphereUniform );
			force.addAssign( sphereForce );

			vertexForceBuffer.element( instanceIndex ).assign( force );
			vertexPositionBuffer.element( instanceIndex ).addAssign( force );

		} )().compute( vertexCount );

	}

	function setupWireframe() {

		// adds helpers to visualize the verlet system

		// verlet vertex visualizer
		const vertexWireframeMaterial = new THREE.SpriteNodeMaterial();
		vertexWireframeMaterial.positionNode = vertexPositionBuffer.element( instanceIndex );
		vertexWireframeObject = new THREE.Mesh( new THREE.PlaneGeometry( 0.01, 0.01 ), vertexWireframeMaterial );
		vertexWireframeObject.frustumCulled = false;
		vertexWireframeObject.count = verletVertices.length;
		scene.add( vertexWireframeObject );


		// verlet spring visualizer
		const springWireframePositionBuffer = new THREE.BufferAttribute( new Float32Array( 6 ), 3, false );
		const springWireframeIndexBuffer = new THREE.BufferAttribute( new Uint32Array( [ 0, 1 ] ), 1, false );
		const springWireframeMaterial = new THREE.LineBasicNodeMaterial();
		springWireframeMaterial.positionNode = Fn( () => {

			const vertexIds = springVertexIdBuffer.element( instanceIndex );
			const vertexId = select( attribute( 'vertexIndex' ).equal( 0 ), vertexIds.x, vertexIds.y );
			return vertexPositionBuffer.element( vertexId );
	
		} )();

		const springWireframeGeometry = new THREE.InstancedBufferGeometry();
		springWireframeGeometry.setAttribute( 'position', springWireframePositionBuffer );
		springWireframeGeometry.setAttribute( 'vertexIndex', springWireframeIndexBuffer );
		springWireframeGeometry.instanceCount = verletSprings.length;

		springWireframeObject = new THREE.Line( springWireframeGeometry, springWireframeMaterial );
		springWireframeObject.frustumCulled = false;
		springWireframeObject.count = verletSprings.length;
		scene.add( springWireframeObject );

	}

	function setupSphere() {

		const geometry = new THREE.IcosahedronGeometry( sphereRadius * 0.95, 4 );
		const material = new THREE.MeshStandardNodeMaterial();
		sphere = new THREE.Mesh( geometry, material );
		scene.add( sphere );

	}

	function setupClothMesh() {

		// This function generates a three Geometry and Mesh to render the cloth based on the verlet systems position data.
		// Therefore it creates a plane mesh, in which each vertex will be centered in the center of 4 verlet vertices.

		const vertexCount = clothNumSegmentsX * clothNumSegmentsY;
		const geometry = new THREE.BufferGeometry();

		// verletVertexIdArray will hold the 4 verlet vertex ids that contribute to each geometry vertex's position
		const verletVertexIdArray = new Uint32Array( vertexCount * 4 );
		const indices = [];

		const getIndex = ( x, y ) => {

			return y * clothNumSegmentsX + x;

		};

		for ( let x = 0; x < clothNumSegmentsX; x ++ ) {

			for ( let y = 0; y < clothNumSegmentsX; y ++ ) {

				const index = getIndex( x, y );
				verletVertexIdArray[ index * 4 ] = verletVertexColumns[ x ][ y ].id;
				verletVertexIdArray[ index * 4 + 1 ] = verletVertexColumns[ x + 1 ][ y ].id;
				verletVertexIdArray[ index * 4 + 2 ] = verletVertexColumns[ x ][ y + 1 ].id;
				verletVertexIdArray[ index * 4 + 3 ] = verletVertexColumns[ x + 1 ][ y + 1 ].id;

				if ( x > 0 && y > 0 ) {

					indices.push( getIndex( x, y ), getIndex( x - 1, y ), getIndex( x - 1, y - 1 ) );
					indices.push( getIndex( x, y ), getIndex( x - 1, y - 1 ), getIndex( x, y - 1 ) );
	
				}
	
			}
	
		}

		const verletVertexIdBuffer = new THREE.BufferAttribute( verletVertexIdArray, 4, false );
		const positionBuffer = new THREE.BufferAttribute( new Float32Array( vertexCount * 3 ), 3, false );
		geometry.setAttribute( 'position', positionBuffer );
		geometry.setAttribute( 'vertexIds', verletVertexIdBuffer );
		geometry.setIndex( indices );

		clothMaterial = new THREE.MeshPhysicalNodeMaterial( {
			side: THREE.DoubleSide,
			transparent: true,
			opacity: 0.85,
			sheen: 1.0,
			sheenRoughness: 0.5,
			sheenColor: new THREE.Color( 0xffffff ),
		} );

		clothMaterial.positionNode = Fn( ( { material } ) => {

			// gather the position of the 4 verlet vertices and calculate the center position and normal from that
			const vertexIds = attribute( 'vertexIds' );
			const v0 = vertexPositionBuffer.element( vertexIds.x ).toVar();
			const v1 = vertexPositionBuffer.element( vertexIds.y ).toVar();
			const v2 = vertexPositionBuffer.element( vertexIds.z ).toVar();
			const v3 = vertexPositionBuffer.element( vertexIds.w ).toVar();

			const top = v0.add( v1 );
			const right = v1.add( v3 );
			const bottom = v2.add( v3 );
			const left = v0.add( v2 );

			const tangent = right.sub( left ).normalize();
			const bitangent = bottom.sub( top ).normalize();

			const normal = cross( tangent, bitangent );

			// send the normalView from the vertex shader to the fragment shader
			material.normalNode = transformNormalToView( normal ).toVarying();

			return v0.add( v1 ).add( v2 ).add( v3 ).mul( 0.25 );
	
		} )();

		clothMesh = new THREE.Mesh( geometry, clothMaterial );
		clothMesh.frustumCulled = false;
		scene.add( clothMesh );

	}

	function setupCloth() {

		setupVerletGeometry();
		setupVerletVertexBuffers();
		setupVerletSpringBuffers();
		setupUniforms();
		setupComputeShaders();
		setupWireframe();
		setupSphere();
		setupClothMesh();

	}

	function onWindowResize() {

		camera.aspect = window.innerWidth / window.innerHeight;

		camera.updateProjectionMatrix();

		renderer.setSize( window.innerWidth, window.innerHeight );

	}

	function updateSphere() {

		sphere.position.set( Math.sin( timestamp * 2.1 ) * 0.1, 0, Math.sin( timestamp * 0.8 ) );
		spherePositionUniform.value.copy( sphere.position );

	}

	async function render() {

		sphere.visible = params.sphere;
		sphereUniform.value = params.sphere ? 1 : 0;
		windUniform.value = params.wind;
		clothMesh.visible = ! params.wireframe;
		vertexWireframeObject.visible = params.wireframe;
		springWireframeObject.visible = params.wireframe;

		const deltaTime = Math.min( clock.getDelta(), 1 / 60 ); // don't advance the time too far, for example when the window is out of focus
		const stepsPerSecond = 360; // ensure the same amount of simulation steps per second on all systems, independent of refresh rate
		const timePerStep = 1 / stepsPerSecond;

		timeSinceLastStep += deltaTime;

		while ( timeSinceLastStep >= timePerStep ) {

			// run a verlet system simulation step
			timestamp += timePerStep;
			timeSinceLastStep -= timePerStep;
			updateSphere();
			await renderer.computeAsync( computeSpringForces );
			await renderer.computeAsync( computeVertexForces );
	
		}

		await renderer.renderAsync( scene, camera );

	}


</script>
</body>
</html>