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HTML 

              
                <html>
	<body>
	</body>
<!-- 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 frameId;

			uniform sampler2D texturePosition;
			uniform sampler2D textureVelocity;

			varying vec2 vUV;
			varying mat2 vUVRot;
			varying float vFrameId;

			uniform float time;

			void main() {

				vec3 pos = texture2D( texturePosition, reference ).xyz;
				vec3 vel = normalize( texture2D( textureVelocity, reference ).xyz );

				vec4 mvPos = modelViewMatrix * vec4( pos, 1.0 );

				gl_PointSize = 20.0 * ( 800.0 / -mvPos.z );

				vUV = vec2( vel.x * 0.5 + 0.5, vel.y * 0.5 + 0.5 );
				vUV = floor( vUV * 11.0 ) / 11.0 + 0.5 / 11.0;
			  // TODO: better movement later
				vUVRot = mat2( 1, 0, 0, 1 );

				vFrameId = floor( mod( frameId + time * 0.5, 9.0 ) );
				gl_Position = projectionMatrix * mvPos;
			}

		</script>

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

			uniform sampler2D texturesBird[ 9 ];

			varying vec2 vUV;
			varying mat2 vUVRot;
			varying float vFrameId;

			uniform vec3 color;

			void main() {
				vec2 uv = 0.9 * vec2( 1.0 / 11.0 ) * ( gl_PointCoord - 0.5 ) * vUVRot + vUV;
				int id = int( vFrameId );
				vec4 col;
				if ( id == 0 ) { col = texture2D( texturesBird[ 0 ], uv ); }
				else if ( id == 1 ) { col = texture2D( texturesBird[ 1 ], uv ); }
				else if ( id == 2 ) { col = texture2D( texturesBird[ 2 ], uv ); }
				else if ( id == 3 ) { col = texture2D( texturesBird[ 3 ], uv ); }
				else if ( id == 4 ) { col = texture2D( texturesBird[ 4 ], uv ); }
				else if ( id == 5 ) { col = texture2D( texturesBird[ 5 ], uv ); }
				else if ( id == 6 ) { col = texture2D( texturesBird[ 6 ], uv ); }
				else if ( id == 7 ) { col = texture2D( texturesBird[ 7 ], uv ); }
				else if ( id == 8 ) { col = texture2D( texturesBird[ 8 ], uv ); }

				gl_FragColor = col;
			}

		</script>
	
</html>
!

CSS 

              
                body {
				background-color: #ffffff;
				margin: 0px;
				overflow: hidden;
				font-family:Monospace;
				font-size:13px;
				text-align:center;
				text-align:center;
				cursor: pointer;
			}

			a {
				color:#0078ff;
			}
!

JS 

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

			var BIRDS = WIDTH * WIDTH;

			var container;
			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;

			var last = performance.now();

			var gpuCompute;
			var velocityVariable;
			var positionVariable;
			var positionUniforms;
			var velocityUniforms;
			var birdUniforms;
			var birdTextures = [];

			init();

			function init() {

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

				loader = new THREE.TextureLoader();
				birdTextures[ 0 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-00.png' );
				birdTextures[ 1 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-01.png' );
				birdTextures[ 2 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-02.png' );
				birdTextures[ 3 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-03.png' );
				birdTextures[ 4 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-04.png' );
				birdTextures[ 5 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-05.png' );
				birdTextures[ 6 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-06.png' );
				birdTextures[ 7 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-07.png' );
				birdTextures[ 8 ] = loader.load( 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/896175/crow-08.png' );

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

				scene = new THREE.Scene();

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

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

				initComputeRenderer();

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

				//

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



				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();

				initBirds();

				animate();
			}

			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.BufferGeometry();
				var positions = new Float32Array( BIRDS * 3 );
				var references = new THREE.BufferAttribute( new Float32Array( BIRDS * 2 ), 2 );
				var frameIds = new THREE.BufferAttribute( new Float32Array( BIRDS ), 1 );

				geometry.addAttribute( 'position', new THREE.BufferAttribute( positions, 3 ) );
				geometry.addAttribute( 'reference', references );
				geometry.addAttribute( 'frameId', frameIds );

				for( var i = 0; i < BIRDS; i++ ) {
					var x = (i % WIDTH) / WIDTH;
					var y = ~~(i / WIDTH) / WIDTH;
					references.array[ i * 2 ] = x;
					references.array[ i * 2 + 1 ] = y;
					frameIds.array[ i ] = Math.random() * 9.0;
				}

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

				var shaderMaterial = new THREE.ShaderMaterial( {

					uniforms: birdUniforms,
					vertexShader: document.getElementById( 'birdVS' ).textContent,
					fragmentShader: document.getElementById( 'birdFS' ).textContent,
					depthTest: false,
					transparent: true
				});

				var particles = new THREE.Points( geometry, shaderMaterial );
				scene.add( particles );
			}

			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();
			}

			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 );

			}
!
999px

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