examples/webgl_gpgpu_birds.html

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		<title>three.js webgl - gpgpu - flocking</title>
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		<div id="info">
			<a href="http://threejs.org" target="_blank" rel="noopener">three.js</a> - <span id="birds"></span> webgl gpgpu birds<br/>
			Select <span id="options"></span> birds<br/>
			Move mouse to disturb birds.

		</div>

		<script src="../build/three.js"></script>
		<script src="js/Detector.js"></script>
		<script src="js/libs/stats.min.js"></script>
		<script src="js/libs/dat.gui.min.js"></script>

		<script src="js/GPUComputationRenderer.js"></script>

		<!--
		TODO: If you're reading this, you may wish to improve this example by
			- Create a better shading for the birds?

		-->


		<!-- shader for bird's position -->
		<script id="fragmentShaderPosition" type="x-shader/x-fragment">

			uniform float time;
			uniform float delta;

			void main()	{

				vec2 uv = gl_FragCoord.xy / resolution.xy;
				vec4 tmpPos = texture2D( texturePosition, uv );
				vec3 position = tmpPos.xyz;
				vec3 velocity = texture2D( textureVelocity, uv ).xyz;

				float phase = tmpPos.w;

				phase = mod( ( phase + delta +
					length( velocity.xz ) * delta * 3. +
					max( velocity.y, 0.0 ) * delta * 6. ), 62.83 );

				gl_FragColor = vec4( position + velocity * delta * 15. , phase );

			}

		</script>

		<!-- shader for bird's velocity -->
		<script id="fragmentShaderVelocity" type="x-shader/x-fragment">

			uniform float time;
			uniform float testing;
			uniform float delta; // about 0.016
			uniform float seperationDistance; // 20
			uniform float alignmentDistance; // 40
			uniform float cohesionDistance; //
			uniform float freedomFactor;
			uniform vec3 predator;

			const float width = resolution.x;
			const float height = resolution.y;

			const float PI = 3.141592653589793;
			const float PI_2 = PI * 2.0;
			// const float VISION = PI * 0.55;

			float zoneRadius = 40.0;
			float zoneRadiusSquared = 1600.0;

			float separationThresh = 0.45;
			float alignmentThresh = 0.65;

			const float UPPER_BOUNDS = BOUNDS;
			const float LOWER_BOUNDS = -UPPER_BOUNDS;

			const float SPEED_LIMIT = 9.0;

			float rand(vec2 co){
				return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);
			}

			void main() {

				zoneRadius = seperationDistance + alignmentDistance + cohesionDistance;
				separationThresh = seperationDistance / zoneRadius;
				alignmentThresh = ( seperationDistance + alignmentDistance ) / zoneRadius;
				zoneRadiusSquared = zoneRadius * zoneRadius;


				vec2 uv = gl_FragCoord.xy / resolution.xy;
				vec3 birdPosition, birdVelocity;

				vec3 selfPosition = texture2D( texturePosition, uv ).xyz;
				vec3 selfVelocity = texture2D( textureVelocity, uv ).xyz;

				float dist;
				vec3 dir; // direction
				float distSquared;

				float seperationSquared = seperationDistance * seperationDistance;
				float cohesionSquared = cohesionDistance * cohesionDistance;

				float f;
				float percent;

				vec3 velocity = selfVelocity;

				float limit = SPEED_LIMIT;

				dir = predator * UPPER_BOUNDS - selfPosition;
				dir.z = 0.;
				// dir.z *= 0.6;
				dist = length( dir );
				distSquared = dist * dist;

				float preyRadius = 150.0;
				float preyRadiusSq = preyRadius * preyRadius;


				// move birds away from predator
				if (dist < preyRadius) {

					f = ( distSquared / preyRadiusSq - 1.0 ) * delta * 100.;
					velocity += normalize( dir ) * f;
					limit += 5.0;
				}


				// if (testing == 0.0) {}
				// if ( rand( uv + time ) < freedomFactor ) {}


				// Attract flocks to the center
				vec3 central = vec3( 0., 0., 0. );
				dir = selfPosition - central;
				dist = length( dir );

				dir.y *= 2.5;
				velocity -= normalize( dir ) * delta * 5.;

				for (float y=0.0;y<height;y++) {
					for (float x=0.0;x<width;x++) {

						vec2 ref = vec2( x + 0.5, y + 0.5 ) / resolution.xy;
						birdPosition = texture2D( texturePosition, ref ).xyz;

						dir = birdPosition - selfPosition;
						dist = length(dir);

						if (dist < 0.0001) continue;

						distSquared = dist * dist;

						if (distSquared > zoneRadiusSquared ) continue;

						percent = distSquared / zoneRadiusSquared;

						if ( percent < separationThresh ) { // low

							// Separation - Move apart for comfort
							f = (separationThresh / percent - 1.0) * delta;
							velocity -= normalize(dir) * f;

						} else if ( percent < alignmentThresh ) { // high

							// Alignment - fly the same direction
							float threshDelta = alignmentThresh - separationThresh;
							float adjustedPercent = ( percent - separationThresh ) / threshDelta;

							birdVelocity = texture2D( textureVelocity, ref ).xyz;

							f = ( 0.5 - cos( adjustedPercent * PI_2 ) * 0.5 + 0.5 ) * delta;
							velocity += normalize(birdVelocity) * f;

						} else {

							// Attraction / Cohesion - move closer
							float threshDelta = 1.0 - alignmentThresh;
							float adjustedPercent = ( percent - alignmentThresh ) / threshDelta;

							f = ( 0.5 - ( cos( adjustedPercent * PI_2 ) * -0.5 + 0.5 ) ) * delta;

							velocity += normalize(dir) * f;

						}

					}

				}


				// this make tends to fly around than down or up
				// if (velocity.y > 0.) velocity.y *= (1. - 0.2 * delta);

				// Speed Limits
				if ( length( velocity ) > limit ) {
					velocity = normalize( velocity ) * limit;
				}

				gl_FragColor = vec4( velocity, 1.0 );

			}

		</script>

		<script type="x-shader/x-vertex" id="birdVS">

			attribute vec2 reference;
			attribute float birdVertex;

			attribute vec3 birdColor;

			uniform sampler2D texturePosition;
			uniform sampler2D textureVelocity;

			varying vec4 vColor;
			varying float z;

			uniform float time;

			void main() {

				vec4 tmpPos = texture2D( texturePosition, reference );
				vec3 pos = tmpPos.xyz;
				vec3 velocity = normalize(texture2D( textureVelocity, reference ).xyz);

				vec3 newPosition = position;

				if ( birdVertex == 4.0 || birdVertex == 7.0 ) {
					// flap wings
					newPosition.y = sin( tmpPos.w ) * 5.;
				}

				newPosition = mat3( modelMatrix ) * newPosition;


				velocity.z *= -1.;
				float xz = length( velocity.xz );
				float xyz = 1.;
				float x = sqrt( 1. - velocity.y * velocity.y );

				float cosry = velocity.x / xz;
				float sinry = velocity.z / xz;

				float cosrz = x / xyz;
				float sinrz = velocity.y / xyz;

				mat3 maty =  mat3(
					cosry, 0, -sinry,
					0    , 1, 0     ,
					sinry, 0, cosry

				);

				mat3 matz =  mat3(
					cosrz , sinrz, 0,
					-sinrz, cosrz, 0,
					0     , 0    , 1
				);

				newPosition =  maty * matz * newPosition;
				newPosition += pos;

				z = newPosition.z;

				vColor = vec4( birdColor, 1.0 );
				gl_Position = projectionMatrix *  viewMatrix  * vec4( newPosition, 1.0 );
			}

		</script>

		<!-- bird geometry shader -->
		<script type="x-shader/x-fragment" id="birdFS">

			varying vec4 vColor;
			varying float z;

			uniform vec3 color;

			void main() {
				// Fake colors for now
				float z2 = 0.2 + ( 1000. - z ) / 1000. * vColor.x;
				gl_FragColor = vec4( z2, z2, z2, 1. );

			}

		</script>


		<script>

			if ( ! Detector.webgl ) Detector.addGetWebGLMessage();

			var hash = document.location.hash.substr( 1 );
			if (hash) hash = parseInt(hash, 0);

			/* TEXTURE WIDTH FOR SIMULATION */
			var WIDTH = hash || 32;

			var BIRDS = WIDTH * WIDTH;

			// Custom Geometry - using 3 triangles each. No UVs, no normals currently.
			THREE.BirdGeometry = function () {

				var triangles = BIRDS * 3;
				var points = triangles * 3;

				THREE.BufferGeometry.call( this );

				var vertices = new THREE.BufferAttribute( new Float32Array( points * 3 ), 3 );
				var birdColors = new THREE.BufferAttribute( new Float32Array( points * 3 ), 3 );
				var references = new THREE.BufferAttribute( new Float32Array( points * 2 ), 2 );
				var birdVertex = new THREE.BufferAttribute( new Float32Array( points ), 1 );

				this.addAttribute( 'position', vertices );
				this.addAttribute( 'birdColor', birdColors );
				this.addAttribute( 'reference', references );
				this.addAttribute( 'birdVertex', birdVertex );

				// this.addAttribute( 'normal', new Float32Array( points * 3 ), 3 );


				var v = 0;

				function verts_push() {
					for (var i=0; i < arguments.length; i++) {
						vertices.array[v++] = arguments[i];
					}
				}

				var wingsSpan = 20;

				for (var f = 0; f<BIRDS; f++ ) {

					// Body
					verts_push(
						0, -0, -20,
						0, 4, -20,
						0, 0, 30
					);

					// Left Wing
					verts_push(
						0, 0, -15,
						-wingsSpan, 0, 0,
						0, 0, 15
					);

					// Right Wing
					verts_push(
						0, 0, 15,
						wingsSpan, 0, 0,
						0, 0, -15
					);

				}

				for( var v = 0; v < triangles * 3; v++ ) {

					var i = ~~(v / 3);
					var x = (i % WIDTH) / WIDTH;
					var y = ~~(i / WIDTH) / WIDTH;

					var c = new THREE.Color(
						0x444444 +
						~~(v / 9) / BIRDS * 0x666666
					);

					birdColors.array[ v * 3 + 0 ] = c.r;
					birdColors.array[ v * 3 + 1 ] = c.g;
					birdColors.array[ v * 3 + 2 ] = c.b;

					references.array[ v * 2     ] = x;
					references.array[ v * 2 + 1 ] = y;

					birdVertex.array[ v         ] = v % 9;

				}

				this.scale( 0.2, 0.2, 0.2 );

			};

			THREE.BirdGeometry.prototype = Object.create( THREE.BufferGeometry.prototype );


			var container, stats;
			var camera, scene, renderer, geometry, i, h, color;
			var mouseX = 0, mouseY = 0;

			var windowHalfX = window.innerWidth / 2;
			var windowHalfY = window.innerHeight / 2;

			var BOUNDS = 800, BOUNDS_HALF = BOUNDS / 2;

			document.getElementById('birds').innerText = BIRDS;

			function change(n) {
				location.hash = n;
				location.reload();
				return false;
			}


			var options = '';
			for (i=1; i<7; i++) {
				var j = Math.pow(2, i);
				options += '<a href="#" onclick="return change(' + j + ')">' + (j * j) + '</a> ';
			}
			document.getElementById('options').innerHTML = options;

			var last = performance.now();

			var gpuCompute;
			var velocityVariable;
			var positionVariable;
			var positionUniforms;
			var velocityUniforms;
			var birdUniforms;

			init();
			animate();

			function init() {

				container = document.createElement( 'div' );
				document.body.appendChild( container );

				camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 1, 3000 );
				camera.position.z = 350;

				scene = new THREE.Scene();
				scene.background = new THREE.Color( 0xffffff );
				scene.fog = new THREE.Fog( 0xffffff, 100, 1000 );

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

				initComputeRenderer();

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

				document.addEventListener( 'mousemove', onDocumentMouseMove, false );
				document.addEventListener( 'touchstart', onDocumentTouchStart, false );
				document.addEventListener( 'touchmove', onDocumentTouchMove, false );

				//

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


				var gui = new dat.GUI();


				var effectController = {
					seperation: 20.0,
					alignment: 20.0,
					cohesion: 20.0,
					freedom: 0.75
				};

				var valuesChanger = function() {

					velocityUniforms.seperationDistance.value = effectController.seperation;
					velocityUniforms.alignmentDistance.value = effectController.alignment;
					velocityUniforms.cohesionDistance.value = effectController.cohesion;
					velocityUniforms.freedomFactor.value = effectController.freedom;

				};

				valuesChanger();


				gui.add( effectController, "seperation", 0.0, 100.0, 1.0 ).onChange( valuesChanger );
				gui.add( effectController, "alignment", 0.0, 100, 0.001 ).onChange( valuesChanger );
				gui.add( effectController, "cohesion", 0.0, 100, 0.025 ).onChange( valuesChanger );
				gui.close();

				initBirds();

			}

			function initComputeRenderer() {

    				gpuCompute = new GPUComputationRenderer( WIDTH, WIDTH, renderer );

				var dtPosition = gpuCompute.createTexture();
				var dtVelocity = gpuCompute.createTexture();
				fillPositionTexture( dtPosition );
				fillVelocityTexture( dtVelocity );

				velocityVariable = gpuCompute.addVariable( "textureVelocity", document.getElementById( 'fragmentShaderVelocity' ).textContent, dtVelocity );
				positionVariable = gpuCompute.addVariable( "texturePosition", document.getElementById( 'fragmentShaderPosition' ).textContent, dtPosition );

				gpuCompute.setVariableDependencies( velocityVariable, [ positionVariable, velocityVariable ] );
				gpuCompute.setVariableDependencies( positionVariable, [ positionVariable, velocityVariable ] );

				positionUniforms = positionVariable.material.uniforms;
				velocityUniforms = velocityVariable.material.uniforms;

				positionUniforms.time = { value: 0.0 };
				positionUniforms.delta = { value: 0.0 };
				velocityUniforms.time = { value: 1.0 };
				velocityUniforms.delta = { value: 0.0 };
				velocityUniforms.testing = { value: 1.0 };
				velocityUniforms.seperationDistance = { value: 1.0 };
				velocityUniforms.alignmentDistance = { value: 1.0 };
				velocityUniforms.cohesionDistance = { value: 1.0 };
				velocityUniforms.freedomFactor = { value: 1.0 };
				velocityUniforms.predator = { value: new THREE.Vector3() };
				velocityVariable.material.defines.BOUNDS = BOUNDS.toFixed( 2 );

				velocityVariable.wrapS = THREE.RepeatWrapping;
				velocityVariable.wrapT = THREE.RepeatWrapping;
				positionVariable.wrapS = THREE.RepeatWrapping;
				positionVariable.wrapT = THREE.RepeatWrapping;

				var error = gpuCompute.init();
				if ( error !== null ) {
				    console.error( error );
				}

			}

			function initBirds() {

				var geometry = new THREE.BirdGeometry();

				// For Vertex and Fragment
				birdUniforms = {
					color: { value: new THREE.Color( 0xff2200 ) },
					texturePosition: { value: null },
					textureVelocity: { value: null },
					time: { value: 1.0 },
					delta: { value: 0.0 }
				};

				// ShaderMaterial
				var material = new THREE.ShaderMaterial( {
					uniforms:       birdUniforms,
					vertexShader:   document.getElementById( 'birdVS' ).textContent,
					fragmentShader: document.getElementById( 'birdFS' ).textContent,
					side: THREE.DoubleSide

				});

				var birdMesh = new THREE.Mesh( geometry, material );
				birdMesh.rotation.y = Math.PI / 2;
				birdMesh.matrixAutoUpdate = false;
				birdMesh.updateMatrix();

				scene.add(birdMesh);

			}

			function fillPositionTexture( texture ) {

				var theArray = texture.image.data;

				for ( var k = 0, kl = theArray.length; k < kl; k += 4 ) {

					var x = Math.random() * BOUNDS - BOUNDS_HALF;
					var y = Math.random() * BOUNDS - BOUNDS_HALF;
					var z = Math.random() * BOUNDS - BOUNDS_HALF;

					theArray[ k + 0 ] = x;
					theArray[ k + 1 ] = y;
					theArray[ k + 2 ] = z;
					theArray[ k + 3 ] = 1;

				}

			}

			function fillVelocityTexture( texture ) {

				var theArray = texture.image.data;

				for ( var k = 0, kl = theArray.length; k < kl; k += 4 ) {

					var x = Math.random() - 0.5;
					var y = Math.random() - 0.5;
					var z = Math.random() - 0.5;

					theArray[ k + 0 ] = x * 10;
					theArray[ k + 1 ] = y * 10;
					theArray[ k + 2 ] = z * 10;
					theArray[ k + 3 ] = 1;

				}

			}


			function onWindowResize() {

				windowHalfX = window.innerWidth / 2;
				windowHalfY = window.innerHeight / 2;

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

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

			}

			function onDocumentMouseMove( event ) {

				mouseX = event.clientX - windowHalfX;
				mouseY = event.clientY - windowHalfY;

			}

			function onDocumentTouchStart( event ) {

				if ( event.touches.length === 1 ) {

					event.preventDefault();

					mouseX = event.touches[ 0 ].pageX - windowHalfX;
					mouseY = event.touches[ 0 ].pageY - windowHalfY;

				}

			}

			function onDocumentTouchMove( event ) {

				if ( event.touches.length === 1 ) {

					event.preventDefault();

					mouseX = event.touches[ 0 ].pageX - windowHalfX;
					mouseY = event.touches[ 0 ].pageY - windowHalfY;

				}

			}

			//

			function animate() {

				requestAnimationFrame( animate );

				render();
				stats.update();

			}

			function render() {

				var now = performance.now();
				var delta = (now - last) / 1000;

				if (delta > 1) delta = 1; // safety cap on large deltas
				last = now;

				positionUniforms.time.value = now;
				positionUniforms.delta.value = delta;
				velocityUniforms.time.value = now;
				velocityUniforms.delta.value = delta;
				birdUniforms.time.value = now;
				birdUniforms.delta.value = delta;

				velocityUniforms.predator.value.set( 0.5 * mouseX / windowHalfX, - 0.5 * mouseY / windowHalfY, 0 );

				mouseX = 10000;
				mouseY = 10000;

				gpuCompute.compute();

				birdUniforms.texturePosition.value = gpuCompute.getCurrentRenderTarget( positionVariable ).texture;
				birdUniforms.textureVelocity.value = gpuCompute.getCurrentRenderTarget( velocityVariable ).texture;

				renderer.render( scene, camera );

			}

		</script>
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