three.js/examples/js/lines/LineSegmentsGeometry.js

( function () {

	const _box = new THREE.Box3();

	const _vector = new THREE.Vector3();

	class LineSegmentsGeometry extends THREE.InstancedBufferGeometry {

		constructor() {

			super();
			this.isLineSegmentsGeometry = true;
			this.type = 'LineSegmentsGeometry';
			const positions = [ - 1, 2, 0, 1, 2, 0, - 1, 1, 0, 1, 1, 0, - 1, 0, 0, 1, 0, 0, - 1, - 1, 0, 1, - 1, 0 ];
			const uvs = [ - 1, 2, 1, 2, - 1, 1, 1, 1, - 1, - 1, 1, - 1, - 1, - 2, 1, - 2 ];
			const index = [ 0, 2, 1, 2, 3, 1, 2, 4, 3, 4, 5, 3, 4, 6, 5, 6, 7, 5 ];
			this.setIndex( index );
			this.setAttribute( 'position', new THREE.Float32BufferAttribute( positions, 3 ) );
			this.setAttribute( 'uv', new THREE.Float32BufferAttribute( uvs, 2 ) );

		}

		applyMatrix4( matrix ) {

			const start = this.attributes.instanceStart;
			const end = this.attributes.instanceEnd;

			if ( start !== undefined ) {

				start.applyMatrix4( matrix );
				end.applyMatrix4( matrix );
				start.needsUpdate = true;

			}

			if ( this.boundingBox !== null ) {

				this.computeBoundingBox();

			}

			if ( this.boundingSphere !== null ) {

				this.computeBoundingSphere();

			}

			return this;

		}

		setPositions( array ) {

			let lineSegments;

			if ( array instanceof Float32Array ) {

				lineSegments = array;

			} else if ( Array.isArray( array ) ) {

				lineSegments = new Float32Array( array );

			}

			const instanceBuffer = new THREE.InstancedInterleavedBuffer( lineSegments, 6, 1 ); // xyz, xyz

			this.setAttribute( 'instanceStart', new THREE.InterleavedBufferAttribute( instanceBuffer, 3, 0 ) ); // xyz

			this.setAttribute( 'instanceEnd', new THREE.InterleavedBufferAttribute( instanceBuffer, 3, 3 ) ); // xyz
			//

			this.computeBoundingBox();
			this.computeBoundingSphere();
			return this;

		}

		setColors( array ) {

			let colors;

			if ( array instanceof Float32Array ) {

				colors = array;

			} else if ( Array.isArray( array ) ) {

				colors = new Float32Array( array );

			}

			const instanceColorBuffer = new THREE.InstancedInterleavedBuffer( colors, 6, 1 ); // rgb, rgb

			this.setAttribute( 'instanceColorStart', new THREE.InterleavedBufferAttribute( instanceColorBuffer, 3, 0 ) ); // rgb

			this.setAttribute( 'instanceColorEnd', new THREE.InterleavedBufferAttribute( instanceColorBuffer, 3, 3 ) ); // rgb

			return this;

		}

		fromWireframeGeometry( geometry ) {

			this.setPositions( geometry.attributes.position.array );
			return this;

		}

		fromEdgesGeometry( geometry ) {

			this.setPositions( geometry.attributes.position.array );
			return this;

		}

		fromMesh( mesh ) {

			this.fromWireframeGeometry( new THREE.WireframeGeometry( mesh.geometry ) ); // set colors, maybe

			return this;

		}

		fromLineSegments( lineSegments ) {

			const geometry = lineSegments.geometry;
			this.setPositions( geometry.attributes.position.array ); // assumes non-indexed
			// set colors, maybe

			return this;

		}

		computeBoundingBox() {

			if ( this.boundingBox === null ) {

				this.boundingBox = new THREE.Box3();

			}

			const start = this.attributes.instanceStart;
			const end = this.attributes.instanceEnd;

			if ( start !== undefined && end !== undefined ) {

				this.boundingBox.setFromBufferAttribute( start );

				_box.setFromBufferAttribute( end );

				this.boundingBox.union( _box );

			}

		}

		computeBoundingSphere() {

			if ( this.boundingSphere === null ) {

				this.boundingSphere = new THREE.Sphere();

			}

			if ( this.boundingBox === null ) {

				this.computeBoundingBox();

			}

			const start = this.attributes.instanceStart;
			const end = this.attributes.instanceEnd;

			if ( start !== undefined && end !== undefined ) {

				const center = this.boundingSphere.center;
				this.boundingBox.getCenter( center );
				let maxRadiusSq = 0;

				for ( let i = 0, il = start.count; i < il; i ++ ) {

					_vector.fromBufferAttribute( start, i );

					maxRadiusSq = Math.max( maxRadiusSq, center.distanceToSquared( _vector ) );

					_vector.fromBufferAttribute( end, i );

					maxRadiusSq = Math.max( maxRadiusSq, center.distanceToSquared( _vector ) );

				}

				this.boundingSphere.radius = Math.sqrt( maxRadiusSq );

				if ( isNaN( this.boundingSphere.radius ) ) {

					console.error( 'THREE.LineSegmentsGeometry.computeBoundingSphere(): Computed radius is NaN. The instanced position data is likely to have NaN values.', this );

				}

			}

		}

		toJSON() { // todo
		}

		applyMatrix( matrix ) {

			console.warn( 'THREE.LineSegmentsGeometry: applyMatrix() has been renamed to applyMatrix4().' );
			return this.applyMatrix4( matrix );

		}

	}

	THREE.LineSegmentsGeometry = LineSegmentsGeometry;

} )();