examples/webgl_clipping_stencil.html

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		<title>three.js webgl - clipping stencil</title>
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		<div id="info"><a href="https://threejs.org" target="_blank" rel="noopener">three.js</a> - solid geometry with clip planes and stencil materials</div>

		<!-- Import maps polyfill -->
		<!-- Remove this when import maps will be widely supported -->
		<script async src="https://unpkg.com/es-module-shims@1.3.6/dist/es-module-shims.js"></script>

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

		<script type="module">
			import * as THREE from 'three';
			import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
			import { GUI } from 'three/addons/libs/lil-gui.module.min.js';
			import Stats from 'three/addons/libs/stats.module.js';

			let camera, scene, renderer, object, stats;
			let planes, planeObjects, planeHelpers;
			let clock;

			const params = {

				animate: true,
				planeX: {

					constant: 0,
					negated: false,
					displayHelper: false

				},
				planeY: {

					constant: 0,
					negated: false,
					displayHelper: false

				},
				planeZ: {

					constant: 0,
					negated: false,
					displayHelper: false

				}


			};

			init();
			animate();

			function createPlaneStencilGroup( geometry, plane, renderOrder ) {

				const group = new THREE.Group();
				const baseMat = new THREE.MeshBasicMaterial();
				baseMat.depthWrite = false;
				baseMat.depthTest = false;
				baseMat.colorWrite = false;
				baseMat.stencilWrite = true;
				baseMat.stencilFunc = THREE.AlwaysStencilFunc;

				// back faces
				const mat0 = baseMat.clone();
				mat0.side = THREE.BackSide;
				mat0.clippingPlanes = [ plane ];
				mat0.stencilFail = THREE.IncrementWrapStencilOp;
				mat0.stencilZFail = THREE.IncrementWrapStencilOp;
				mat0.stencilZPass = THREE.IncrementWrapStencilOp;

				const mesh0 = new THREE.Mesh( geometry, mat0 );
				mesh0.renderOrder = renderOrder;
				group.add( mesh0 );

				// front faces
				const mat1 = baseMat.clone();
				mat1.side = THREE.FrontSide;
				mat1.clippingPlanes = [ plane ];
				mat1.stencilFail = THREE.DecrementWrapStencilOp;
				mat1.stencilZFail = THREE.DecrementWrapStencilOp;
				mat1.stencilZPass = THREE.DecrementWrapStencilOp;

				const mesh1 = new THREE.Mesh( geometry, mat1 );
				mesh1.renderOrder = renderOrder;

				group.add( mesh1 );

				return group;

			}

			function init() {

				clock = new THREE.Clock();

				scene = new THREE.Scene();

				camera = new THREE.PerspectiveCamera( 36, window.innerWidth / window.innerHeight, 1, 100 );
				camera.position.set( 2, 2, 2 );

				scene.add( new THREE.AmbientLight( 0xffffff, 0.5 ) );

				const dirLight = new THREE.DirectionalLight( 0xffffff, 1 );
				dirLight.position.set( 5, 10, 7.5 );
				dirLight.castShadow = true;
				dirLight.shadow.camera.right = 2;
				dirLight.shadow.camera.left = - 2;
				dirLight.shadow.camera.top	= 2;
				dirLight.shadow.camera.bottom = - 2;

				dirLight.shadow.mapSize.width = 1024;
				dirLight.shadow.mapSize.height = 1024;
				scene.add( dirLight );

				planes = [
					new THREE.Plane( new THREE.Vector3( - 1, 0, 0 ), 0 ),
					new THREE.Plane( new THREE.Vector3( 0, - 1, 0 ), 0 ),
					new THREE.Plane( new THREE.Vector3( 0, 0, - 1 ), 0 )
				];

				planeHelpers = planes.map( p => new THREE.PlaneHelper( p, 2, 0xffffff ) );
				planeHelpers.forEach( ph => {

					ph.visible = false;
					scene.add( ph );

				} );

				const geometry = new THREE.TorusKnotGeometry( 0.4, 0.15, 220, 60 );
				object = new THREE.Group();
				scene.add( object );

				// Set up clip plane rendering
				planeObjects = [];
				const planeGeom = new THREE.PlaneGeometry( 4, 4 );

				for ( let i = 0; i < 3; i ++ ) {

					const poGroup = new THREE.Group();
					const plane = planes[ i ];
					const stencilGroup = createPlaneStencilGroup( geometry, plane, i + 1 );

					// plane is clipped by the other clipping planes
					const planeMat =
						new THREE.MeshStandardMaterial( {

							color: 0xE91E63,
							metalness: 0.1,
							roughness: 0.75,
							clippingPlanes: planes.filter( p => p !== plane ),

							stencilWrite: true,
							stencilRef: 0,
							stencilFunc: THREE.NotEqualStencilFunc,
							stencilFail: THREE.ReplaceStencilOp,
							stencilZFail: THREE.ReplaceStencilOp,
							stencilZPass: THREE.ReplaceStencilOp,

						} );
					const po = new THREE.Mesh( planeGeom, planeMat );
					po.onAfterRender = function ( renderer ) {

						renderer.clearStencil();

					};

					po.renderOrder = i + 1.1;

					object.add( stencilGroup );
					poGroup.add( po );
					planeObjects.push( po );
					scene.add( poGroup );

				}

				const material = new THREE.MeshStandardMaterial( {

					color: 0xFFC107,
					metalness: 0.1,
					roughness: 0.75,
					clippingPlanes: planes,
					clipShadows: true,
					shadowSide: THREE.DoubleSide,

				} );

				// add the color
				const clippedColorFront = new THREE.Mesh( geometry, material );
				clippedColorFront.castShadow = true;
				clippedColorFront.renderOrder = 6;
				object.add( clippedColorFront );


				const ground = new THREE.Mesh(
					new THREE.PlaneGeometry( 9, 9, 1, 1 ),
					new THREE.ShadowMaterial( { color: 0x000000, opacity: 0.25, side: THREE.DoubleSide } )
				);

				ground.rotation.x = - Math.PI / 2; // rotates X/Y to X/Z
				ground.position.y = - 1;
				ground.receiveShadow = true;
				scene.add( ground );

				// Stats
				stats = new Stats();
				document.body.appendChild( stats.dom );

				// Renderer
				renderer = new THREE.WebGLRenderer( { antialias: true } );
				renderer.shadowMap.enabled = true;
				renderer.setPixelRatio( window.devicePixelRatio );
				renderer.setSize( window.innerWidth, window.innerHeight );
				renderer.setClearColor( 0x263238 );
				window.addEventListener( 'resize', onWindowResize );
				document.body.appendChild( renderer.domElement );

				renderer.localClippingEnabled = true;

				// Controls
				const controls = new OrbitControls( camera, renderer.domElement );
				controls.minDistance = 2;
				controls.maxDistance = 20;
				controls.update();

				// GUI
				const gui = new GUI();
				gui.add( params, 'animate' );

				const planeX = gui.addFolder( 'planeX' );
				planeX.add( params.planeX, 'displayHelper' ).onChange( v => planeHelpers[ 0 ].visible = v );
				planeX.add( params.planeX, 'constant' ).min( - 1 ).max( 1 ).onChange( d => planes[ 0 ].constant = d );
				planeX.add( params.planeX, 'negated' ).onChange( () => {

					planes[ 0 ].negate();
					params.planeX.constant = planes[ 0 ].constant;

				} );
				planeX.open();

				const planeY = gui.addFolder( 'planeY' );
				planeY.add( params.planeY, 'displayHelper' ).onChange( v => planeHelpers[ 1 ].visible = v );
				planeY.add( params.planeY, 'constant' ).min( - 1 ).max( 1 ).onChange( d => planes[ 1 ].constant = d );
				planeY.add( params.planeY, 'negated' ).onChange( () => {

					planes[ 1 ].negate();
					params.planeY.constant = planes[ 1 ].constant;

				} );
				planeY.open();

				const planeZ = gui.addFolder( 'planeZ' );
				planeZ.add( params.planeZ, 'displayHelper' ).onChange( v => planeHelpers[ 2 ].visible = v );
				planeZ.add( params.planeZ, 'constant' ).min( - 1 ).max( 1 ).onChange( d => planes[ 2 ].constant = d );
				planeZ.add( params.planeZ, 'negated' ).onChange( () => {

					planes[ 2 ].negate();
					params.planeZ.constant = planes[ 2 ].constant;

				} );
				planeZ.open();

			}

			function onWindowResize() {

				camera.aspect = window.innerWidth / window.innerHeight;
				camera.updateProjectionMatrix();

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

			}

			function animate() {

				const delta = clock.getDelta();

				requestAnimationFrame( animate );

				if ( params.animate ) {

					object.rotation.x += delta * 0.5;
					object.rotation.y += delta * 0.2;

				}

				for ( let i = 0; i < planeObjects.length; i ++ ) {

					const plane = planes[ i ];
					const po = planeObjects[ i ];
					plane.coplanarPoint( po.position );
					po.lookAt(
						po.position.x - plane.normal.x,
						po.position.y - plane.normal.y,
						po.position.z - plane.normal.z,
					);

				}

				stats.begin();
				renderer.render( scene, camera );
				stats.end();

			}

		</script>

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