three.js/src/math/Line3.js

/**
 * @author bhouston / http://exocortex.com
 */

THREE.Line3 = function ( start, end ) {

	this.start = ( start !== undefined ) ? start : new THREE.Vector3();
	this.end = ( end !== undefined ) ? end : new THREE.Vector3();

};

THREE.extend( THREE.Line3.prototype, {

	set: function ( start, end ) {

		this.start.copy( start );
		this.end.copy( end );

		return this;

	},

	copy: function ( line ) {

		this.start.copy( line.start );
		this.end.copy( line.end );

		return this;

	},

	center: function ( optionalTarget ) {

		var result = optionalTarget || new THREE.Vector3();
		return result.addVectors( this.start, this.end ).multiplyScalar( 0.5 );

	},

	delta: function ( optionalTarget ) {

		var result = optionalTarget || new THREE.Vector3();
		return result.subVectors( this.end, this.start );

	},

	distanceSq: function () {

		return this.start.distanceToSquared( this.end );

	},

	distance: function () {

		return this.start.distanceTo( this.end );

	},

	at: function ( t, optionalTarget ) {

		var result = optionalTarget || new THREE.Vector3();

		return this.delta( result ).multiplyScalar( t ).add( this.start );

	},

	closestPointToPointParameter: function() {

		var startP = new THREE.Vector3();
		var startEnd = new THREE.Vector3();

		return function ( point, clampToLine ) {
		
			startP.subVectors( point, this.start );
			startEnd.subVectors( this.end, this.start );

			var startEnd2 = startEnd.dot( startEnd );
			var startEnd_startP = startEnd.dot( startP );

			var t = startEnd_startP / startEnd2;

			if( clampToLine ) {
				
	        	t = THREE.Math.clamp( t, 0, 1 );

	        }

	        return t;

		};

	}(),

	closestPointToPoint: function ( point, clampToLine, optionalTarget ) {

		var t = this.closestPointToPointParameter( point, clampToLine );

		var result = optionalTarget || new THREE.Vector3();			

        return this.delta( result ).multiplyScalar( t ).add( this.start );

	},

	applyMatrix4: function ( matrix ) {

		this.start.applyMatrix4( matrix );
		this.end.applyMatrix4( matrix );

		return this;

	},

	equals: function ( line ) {

		return line.start.equals( this.start ) && line.end.equals( this.end );

	},

	clone: function () {

		return new THREE.Line3().copy( this );

	}

} );