examples/webgl_buffergeometry_lines_indexed.html

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		<title>three.js webgl - buffergeometry - lines - indexed</title>
		<meta charset="utf-8">
		<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
		<link type="text/css" rel="stylesheet" href="main.css">
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		<div id="container"></div>
		<div id="info"><a href="https://threejs.org" target="_blank" rel="noopener">three.js</a> webgl - buffergeometry - lines - indexed</div>


		<script type="importmap">
			{
				"imports": {
					"three": "../build/three.module.js",
					"three/addons/": "./jsm/"
				}
			}
		</script>

		<script type="module">

			import * as THREE from 'three';

			import Stats from 'three/addons/libs/stats.module.js';

			let container, stats;

			let camera, scene, renderer;

			let parent_node;

			init();

			function init() {

				container = document.getElementById( 'container' );

				camera = new THREE.PerspectiveCamera( 27, window.innerWidth / window.innerHeight, 1, 10000 );
				camera.position.z = 9000;

				scene = new THREE.Scene();

				const geometry = new THREE.BufferGeometry();
				const material = new THREE.LineBasicMaterial( { vertexColors: true } );

				const indices = [];
				const positions = [];
				const colors = [];

				let next_positions_index = 0;

				//

				const iteration_count = 4;
				const rangle = 60 * Math.PI / 180.0;

				function add_vertex( v ) {

					positions.push( v.x, v.y, v.z );
					colors.push( Math.random() * 0.5 + 0.5, Math.random() * 0.5 + 0.5, 1 );

					return next_positions_index ++;

				}

				// simple Koch curve

				function snowflake_iteration( p0, p4, depth ) {

					if ( -- depth < 0 ) {

						const i = next_positions_index - 1; // p0 already there
						add_vertex( p4 );
						indices.push( i, i + 1 );

						return;

					}

					const v = p4.clone().sub( p0 );
					const v_tier = v.clone().multiplyScalar( 1 / 3 );
					const p1 = p0.clone().add( v_tier );

					const angle = Math.atan2( v.y, v.x ) + rangle;
					const length = v_tier.length();
					const p2 = p1.clone();
					p2.x += Math.cos( angle ) * length;
					p2.y += Math.sin( angle ) * length;

					const p3 = p0.clone().add( v_tier ).add( v_tier );

					snowflake_iteration( p0, p1, depth );
					snowflake_iteration( p1, p2, depth );
					snowflake_iteration( p2, p3, depth );
					snowflake_iteration( p3, p4, depth );

				}

				function snowflake( points, loop, x_offset ) {

					for ( let iteration = 0; iteration != iteration_count; iteration ++ ) {

						add_vertex( points[ 0 ] );

						for ( let p_index = 0, p_count = points.length - 1; p_index != p_count; p_index ++ ) {

							snowflake_iteration( points[ p_index ], points[ p_index + 1 ], iteration );

						}

						if ( loop ) snowflake_iteration( points[ points.length - 1 ], points[ 0 ], iteration );

						// translate input curve for next iteration

						for ( let p_index = 0, p_count = points.length; p_index != p_count; p_index ++ ) {

							points[ p_index ].x += x_offset;

						}

					}

				}

				let y = 0;

				snowflake(
					[
						new THREE.Vector3( 0, y, 0 ),
						new THREE.Vector3( 500, y, 0 )
					],
					false, 600
				);

				y += 600;
				snowflake(
					[
						new THREE.Vector3( 0, y, 0 ),
						new THREE.Vector3( 250, y + 400, 0 ),
						new THREE.Vector3( 500, y, 0 )
					],
					true, 600
				);

				y += 600;
				snowflake(
					[
						new THREE.Vector3( 0, y, 0 ),
						new THREE.Vector3( 500, y, 0 ),
						new THREE.Vector3( 500, y + 500, 0 ),
						new THREE.Vector3( 0, y + 500, 0 )
					],
					true, 600
				);

				y += 1000;
				snowflake(
					[
						new THREE.Vector3( 250, y, 0 ),
						new THREE.Vector3( 500, y, 0 ),
						new THREE.Vector3( 250, y, 0 ),
						new THREE.Vector3( 250, y + 250, 0 ),
						new THREE.Vector3( 250, y, 0 ),
						new THREE.Vector3( 0, y, 0 ),
						new THREE.Vector3( 250, y, 0 ),
						new THREE.Vector3( 250, y - 250, 0 ),
						new THREE.Vector3( 250, y, 0 )
					],
					false, 600
				);

				//

				geometry.setIndex( indices );
				geometry.setAttribute( 'position', new THREE.Float32BufferAttribute( positions, 3 ) );
				geometry.setAttribute( 'color', new THREE.Float32BufferAttribute( colors, 3 ) );
				geometry.computeBoundingSphere();

				const lineSegments = new THREE.LineSegments( geometry, material );
				lineSegments.position.x -= 1200;
				lineSegments.position.y -= 1200;

				parent_node = new THREE.Object3D();
				parent_node.add( lineSegments );

				scene.add( parent_node );

				renderer = new THREE.WebGLRenderer();
				renderer.setPixelRatio( window.devicePixelRatio );
				renderer.setSize( window.innerWidth, window.innerHeight );
				renderer.setAnimationLoop( animate );

				container.appendChild( renderer.domElement );

				//

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

				//

				window.addEventListener( 'resize', onWindowResize );

			}

			function onWindowResize() {

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

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

			}

			//

			function animate() {

				const time = Date.now() * 0.001;

				parent_node.rotation.z = time * 0.5;

				renderer.render( scene, camera );

				stats.update();

			}

		</script>

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