done_webgl_interactive_cubes_gpu.html

<!DOCTYPE html>
<html lang="en">
	<head>
		<title>three.js webgl - interactive cubes (gpu)</title>
		<meta charset="utf-8">
		<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
		<style>
			body {
				font-family: Monospace;
				background-color: #f0f0f0;
				margin: 0px;
				overflow: hidden;
			}

			.info {
				position: absolute;
				background-color: black;
				opacity: 0.8;
				color: white;
				text-align: center;
				top: 0px;
				width: 100%;
			}

			.info a {
				color: #00ffff;
			}
		</style>
	</head>
	<body>

		<div class="info">
			<a href="http://threejs.org" target="_blank" rel="noopener">three.js</a> webgl - gpu picking
		</div>

		<div id="container"></div>

		<script src="../build/three.js"></script>

		<script src="js/controls/TrackballControls.js"></script>

		<script src="js/libs/stats.min.js"></script>

		<script>

			var container, stats;
			var camera, controls, scene, renderer;
			var pickingData = [], pickingTexture, pickingScene;
			var objects = [];
			var highlightBox;

			var mouse = new THREE.Vector2();
			var offset = new THREE.Vector3( 10, 10, 10 );

			init();
			animate();

			function init() {

				container = document.getElementById( "container" );

				camera = new THREE.PerspectiveCamera( 70, window.innerWidth / window.innerHeight, 1, 10000 );
				camera.position.z = 1000;

                //about TrackballControls setting.
				controls = new THREE.TrackballControls( camera );
				controls.rotateSpeed = 1.0;
				controls.zoomSpeed = 1.2;
				controls.panSpeed = 0.8;
				controls.noZoom = false;
				controls.noPan = false;
				controls.staticMoving = true;
				controls.dynamicDampingFactor = 0.3;

				scene = new THREE.Scene();

                //https://threejs.org/docs/index.html#api/renderers/WebGLRenderTarget
                //https://threejs.org/docs/index.html#api/constants/Textures
				pickingScene = new THREE.Scene();
				pickingTexture = new THREE.WebGLRenderTarget( window.innerWidth, window.innerHeight );
				pickingTexture.texture.minFilter = THREE.LinearMipMapLinearFilter; //use this to set the computation mode when one texture element cover more than one pixel
                

                //https://threejs.org/docs/index.html#api/lights/AmbientLight
                //global light 
				scene.add( new THREE.AmbientLight( 0x555555 ) );

				var light = new THREE.SpotLight( 0xffffff, 1.5 );
				light.position.set( 0, 500, 2000 );
				scene.add( light );

                
                //create texture for the picking objects.
				var geometry = new THREE.Geometry(),
				pickingGeometry = new THREE.Geometry(),
				pickingMaterial = new THREE.MeshBasicMaterial( { vertexColors: THREE.VertexColors } ),
				defaultMaterial = new THREE.MeshPhongMaterial({ color: 0xffffff, shading: THREE.FlatShading, vertexColors: THREE.VertexColors, shininess: 0	} );

                
				function applyVertexColors( g, c ) {

					g.faces.forEach( function( f ) {

						var n = ( f instanceof THREE.Face3 ) ? 3 : 4;

						for( var j = 0; j < n; j ++ ) {

							f.vertexColors[ j ] = c;

						}

					} );

				}

				var geom = new THREE.BoxGeometry( 1, 1, 1 );
				var color = new THREE.Color();

				var matrix = new THREE.Matrix4();
				var quaternion = new THREE.Quaternion();

				for ( var i = 0; i < 5000; i ++ ) {

					var position = new THREE.Vector3();
					position.x = Math.random() * 10000 - 5000;
					position.y = Math.random() * 6000 - 3000;
					position.z = Math.random() * 8000 - 4000;

					var rotation = new THREE.Euler();
					rotation.x = Math.random() * 2 * Math.PI;
					rotation.y = Math.random() * 2 * Math.PI;
					rotation.z = Math.random() * 2 * Math.PI;

					var scale = new THREE.Vector3();
					scale.x = Math.random() * 200 + 100;
					scale.y = Math.random() * 200 + 100;
					scale.z = Math.random() * 200 + 100;

                    
                    //transfrom value of Euler to quaternion to prevent the situation of dead lock
                    //the second argument did not have explanation in offical doc and change it to true, not have effect on the display after test.
					quaternion.setFromEuler( rotation, false );
                    
                    //combine all together to get the position matrix.
					matrix.compose( position, quaternion, scale );

					// give the geom's vertices a random color, to be displayed
					applyVertexColors( geom, color.setHex( Math.random() * 0xffffff ) );

                    //apply the transfrom to the geometry
					geometry.merge( geom, matrix );

					// give the geom's vertices a color corresponding to the "id"
                    // you set id here as a kind of color, will be used to do bit shift to get this value.
					applyVertexColors( geom, color.setHex( i ) );


					pickingGeometry.merge( geom, matrix );

					pickingData[ i ] = {

						position: position,
						rotation: rotation,
						scale: scale

					};

				}

				var drawnObject = new THREE.Mesh( geometry, defaultMaterial );
				scene.add( drawnObject );

				pickingScene.add( new THREE.Mesh( pickingGeometry, pickingMaterial ) );

				highlightBox = new THREE.Mesh(
					new THREE.BoxGeometry( 1, 1, 1 ),
					new THREE.MeshLambertMaterial( { color: 0xffff00 }
				) );//https://threejs.org/docs/index.html#api/materials/MeshLambertMaterial
				scene.add( highlightBox );

				renderer = new THREE.WebGLRenderer( { antialias: true } );
				renderer.setClearColor( 0xffffff );  //background, can set alpha in the second
				renderer.setPixelRatio( window.devicePixelRatio );  //set the solution
				renderer.setSize( window.innerWidth, window.innerHeight ); //fit the screen
				renderer.sortObjects = false; //involve transparency, should be turn off when you used other methods about transparency
				container.appendChild( renderer.domElement );

				stats = new Stats();
				container.appendChild( stats.dom );

				renderer.domElement.addEventListener( 'mousemove', onMouseMove );

			}

			//

			function onMouseMove( e ) {

				mouse.x = e.clientX;
				mouse.y = e.clientY;

			}

			function animate() {

				requestAnimationFrame( animate );

				render();
				stats.update();

			}

			function pick() {

				//render the picking scene off-screen

				renderer.render( pickingScene, camera, pickingTexture );

				//create buffer for reading single pixel
				var pixelBuffer = new Uint8Array( 4 );

				//read the pixel under the mouse from the texture
                //https://threejs.org/docs/index.html#api/renderers/WebGLRenderer
                //Question: why the height should be pickingTexture.height - mouse.y
				renderer.readRenderTargetPixels(pickingTexture, mouse.x, pickingTexture.height - mouse.y, 1, 1, pixelBuffer);

				//interpret the pixel as an ID

				var id = ( pixelBuffer[0] << 16 ) | ( pixelBuffer[1] << 8 ) | ( pixelBuffer[2] );
				var data = pickingData[ id ];

				if ( data) {

					//move our highlightBox so that it surrounds the picked object

					if ( data.position && data.rotation && data.scale ){

						highlightBox.position.copy( data.position );
						highlightBox.rotation.copy( data.rotation );
						highlightBox.scale.copy( data.scale ).add( offset );
						highlightBox.visible = true;

					}

				} else {

					highlightBox.visible = false;

				}

			}

			function render() {

				controls.update();

				pick();

				renderer.render( scene, camera );

			}

		</script>

	</body>
</html>