examples/webgl_geometry_colors_lookuptable.html

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	<head>
		<title>three.js webgl - lookup table</title>
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			body {
				background-color: #fff;
				color: #444;
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			a {
				color: red;
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		</style>
	</head>
	<body>

		<div id="info">
			<a href="https://threejs.org" target="_blank" rel="noopener">three.js</a> webgl - lookup table<br/>
			vertex color values from a range of data values
		</div>

		<div id="container"></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 { GUI } from 'three/addons/libs/lil-gui.module.min.js';

			import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
			import { Lut } from 'three/addons/math/Lut.js';

			let container;

			let perpCamera, orthoCamera, renderer, lut;

			let mesh, sprite;
			let scene, uiScene;

			let params;

			init();

			function init() {

				container = document.getElementById( 'container' );

				scene = new THREE.Scene();
				scene.background = new THREE.Color( 0xffffff );

				uiScene = new THREE.Scene();

				lut = new Lut();

				const width = window.innerWidth;
				const height = window.innerHeight;

				perpCamera = new THREE.PerspectiveCamera( 60, width / height, 1, 100 );
				perpCamera.position.set( 0, 0, 10 );
				scene.add( perpCamera );

				orthoCamera = new THREE.OrthographicCamera( - 1, 1, 1, - 1, 1, 2 );
				orthoCamera.position.set( 0.5, 0, 1 );

				sprite = new THREE.Sprite( new THREE.SpriteMaterial( {
					map: new THREE.CanvasTexture( lut.createCanvas() )
				} ) );
				sprite.scale.x = 0.125;
				uiScene.add( sprite );

				mesh = new THREE.Mesh( undefined, new THREE.MeshLambertMaterial( {
					side: THREE.DoubleSide,
					color: 0xF5F5F5,
					vertexColors: true
				} ) );
				scene.add( mesh );

				params	= {
					colorMap: 'rainbow',
				};
				loadModel( );

				const pointLight = new THREE.PointLight( 0xffffff, 1 );
				perpCamera.add( pointLight );

				renderer = new THREE.WebGLRenderer( { antialias: true } );
				renderer.autoClear = false;
				renderer.setPixelRatio( window.devicePixelRatio );
				renderer.setSize( width, height );
				container.appendChild( renderer.domElement );

				window.addEventListener( 'resize', onWindowResize );

				const controls = new OrbitControls( perpCamera, renderer.domElement );
				controls.addEventListener( 'change', render );

				const gui = new GUI();

				gui.add( params, 'colorMap', [ 'rainbow', 'cooltowarm', 'blackbody', 'grayscale' ] ).onChange( function () {

					updateColors();
					render();

				} );

			}

			function onWindowResize() {

				const width = window.innerWidth;
				const height = window.innerHeight;

				perpCamera.aspect = width / height;
				perpCamera.updateProjectionMatrix();

				renderer.setSize( width, height );
				render();

			}

			function render() {

				renderer.clear();
				renderer.render( scene, perpCamera );
				renderer.render( uiScene, orthoCamera );

			}

			function loadModel( ) {

				const loader = new THREE.BufferGeometryLoader();
				loader.load( 'models/json/pressure.json', function ( geometry ) {

					geometry.center();
					geometry.computeVertexNormals();

					// default color attribute
					const colors = [];

					for ( let i = 0, n = geometry.attributes.position.count; i < n; ++ i ) {

						colors.push( 1, 1, 1 );

					}

					geometry.setAttribute( 'color', new THREE.Float32BufferAttribute( colors, 3 ) );

					mesh.geometry = geometry;
					updateColors();

					render();

				} );

			}

			function updateColors() {

				lut.setColorMap( params.colorMap );

				lut.setMax( 2000 );
				lut.setMin( 0 );

				const geometry = mesh.geometry;
				const pressures = geometry.attributes.pressure;
				const colors = geometry.attributes.color;

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

					const colorValue = pressures.array[ i ];

					const color = lut.getColor( colorValue );

					if ( color === undefined ) {

						console.log( 'Unable to determine color for value:', colorValue );

					} else {

						colors.setXYZ( i, color.r, color.g, color.b );

					}

				}

				colors.needsUpdate = true;

				const map = sprite.material.map;
				lut.updateCanvas( map.image );
				map.needsUpdate = true;

			}

		</script>

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