examples/webgl_nearestneighbour.html

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		<title>three.js webgl - nearest neighbour</title>
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		<div id="info"><a href="http://threejs.org" target="_blank" rel="noopener">three.js</a> webgl - typed arrays - nearest neighbour for 500,000 sprites</div>

		<script src="../build/three.js"></script>
		<script src="js/utils/TypedArrayUtils.js"></script>
		<script src="js/controls/FirstPersonControls.js"></script>
		<script type="x-shader/x-vertex" id="vertexshader">

			//uniform float zoom;

			attribute float alpha;

			varying float vAlpha;

			void main() {

				vAlpha = 1.0 - alpha;

				vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );

				gl_PointSize = 4.0 * ( 300.0 / -mvPosition.z );

				gl_Position = projectionMatrix * mvPosition;

			}

		</script>

		<script type="x-shader/x-fragment" id="fragmentshader">

			uniform sampler2D tex1;

			varying float vAlpha;

			void main() {

				gl_FragColor = texture2D( tex1, gl_PointCoord );
				gl_FragColor.r = ( 1.0 - gl_FragColor.r ) * vAlpha + gl_FragColor.r;

			}

		</script>
		<script>

			var camera, scene, renderer;
			var controls;

			var amountOfParticles = 500000, maxDistance = Math.pow( 120, 2 );
			var positions, alphas, particles, _particleGeom;
			var kdtree;

			var clock = new THREE.Clock();

			function init() {

				camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 1, 1000000 );

				scene = new THREE.Scene();

				controls = new THREE.FirstPersonControls( camera );
				controls.movementSpeed = 100;
				controls.lookSpeed = 0.1;

				controls.lookAt( 500, 500, 500 );


				// add a skybox background
				var cubeTextureLoader = new THREE.CubeTextureLoader();

				cubeTextureLoader.setPath( 'textures/cube/skybox/' );

				var cubeTexture = cubeTextureLoader.load( [
					'px.jpg', 'nx.jpg',
					'py.jpg', 'ny.jpg',
					'pz.jpg', 'nz.jpg',
				] );

				scene.background = cubeTexture;

				//

				renderer = new THREE.WebGLRenderer();
				renderer.setPixelRatio( window.devicePixelRatio );
				renderer.setSize( window.innerWidth, window.innerHeight );
				document.body.appendChild( renderer.domElement );

				// create the custom shader

				var textureLoader = new THREE.TextureLoader();

				var imagePreviewTexture = textureLoader.load( 'textures/crate.gif' );

				imagePreviewTexture.minFilter = THREE.LinearMipMapLinearFilter;
				imagePreviewTexture.magFilter = THREE.LinearFilter;

				var pointShaderMaterial = new THREE.ShaderMaterial( {
					uniforms: {
						tex1: { value: imagePreviewTexture },
						zoom: { value: 9.0 }
					},
					vertexShader: document.getElementById( 'vertexshader' ).textContent,
					fragmentShader: document.getElementById( 'fragmentshader' ).textContent,
					transparent: true
				} );


				//create particles with buffer geometry
				var distanceFunction = function ( a, b ) {

					return Math.pow( a[ 0 ] - b[ 0 ], 2 ) + Math.pow( a[ 1 ] - b[ 1 ], 2 ) + Math.pow( a[ 2 ] - b[ 2 ], 2 );

				};

				positions = new Float32Array( amountOfParticles * 3 );
				alphas = new Float32Array( amountOfParticles );

				_particleGeom = new THREE.BufferGeometry();
				_particleGeom.addAttribute( 'position', new THREE.BufferAttribute( positions, 3 ) );
				_particleGeom.addAttribute( 'alpha', new THREE.BufferAttribute( alphas, 1 ) );

				particles = new THREE.Points( _particleGeom, pointShaderMaterial );

				for ( var x = 0; x < amountOfParticles; x ++ ) {

					positions[ x * 3 + 0 ] = Math.random() * 1000;
					positions[ x * 3 + 1 ] = Math.random() * 1000;
					positions[ x * 3 + 2 ] = Math.random() * 1000;

					alphas[ x ] = 1.0;

				}


				var measureStart = new Date().getTime();

				// creating the kdtree takes a lot of time to execute, in turn the nearest neighbour search will be much faster
				kdtree = new THREE.TypedArrayUtils.Kdtree( positions, distanceFunction, 3 );

				console.log( 'TIME building kdtree', new Date().getTime() - measureStart );

				// display particles after the kd-tree was generated and the sorting of the positions-array is done
				scene.add( particles );

				window.addEventListener( 'resize', onWindowResize, false );

			}

			function onWindowResize() {

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

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

				controls.handleResize();

			}

			function animate() {

				requestAnimationFrame( animate );

				//
				displayNearest( camera.position );

				controls.update( clock.getDelta() );

				renderer.render( scene, camera );

			}

			function displayNearest( position ) {

				// take the nearest 200 around him. distance^2 'cause we use the manhattan distance and no square is applied in the distance function
				var imagePositionsInRange = kdtree.nearest( [ position.x, position.y, position.z ], 100, maxDistance );

				// We combine the nearest neighbour with a view frustum. Doesn't make sense if we change the sprites not in our view... well maybe it does. Whatever you want.
				var _frustum = new THREE.Frustum();
				var _projScreenMatrix = new THREE.Matrix4();

				_projScreenMatrix.multiplyMatrices( camera.projectionMatrix, camera.matrixWorldInverse );
				_frustum.setFromMatrix( _projScreenMatrix );

				for ( var i = 0, il = imagePositionsInRange.length; i < il; i ++ ) {

					var object = imagePositionsInRange[ i ];
					var objectPoint = new THREE.Vector3().fromArray( object[ 0 ].obj );

					if ( _frustum.containsPoint( objectPoint ) ) {

						var objectIndex = object[ 0 ].pos;

						// set the alpha according to distance
						alphas[ objectIndex ] = 1.0 / maxDistance * object[ 1 ];

						// update the attribute
						_particleGeom.attributes.alpha.needsUpdate = true;

					}

				}

			}


			init();
			animate();

		</script>
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