IKRS.CubicBezierCurve.js~

/**
 * @author Ikaros Kappler
 * @date 2013-08-15
 * @version 1.0.0
 **/

IKRS.CubicBezierCurve = function ( p_startPoint,        // THREE.Vector2
				   p_endPoint,          // THREE.Vector2
				   p_startControlPoint, // THREE.Vector2
				   p_endControlPoint   // THREE.Vector2
				 ) {
    
    //window.alert( "[IKRS.CubicBezierCurve] constructor called." );
    
    // Call super constructor
    IKRS.Object.call( this );
        
    // p0: start of the curve
    // p3: end of the curve
    
    // p1: help-point of p0
    // p2: help-point of p3
    
    this.startPoint         = p_startPoint;
    this.startControlPoint  = p_startControlPoint;
    this.endPoint           = p_endPoint;
    this.endControlPoint    = p_endControlPoint;
    
    
    this.curveIntervals     = 30;
    
    this.segmentCache       = [];
    this.segmentLengths     = [];
    this.arcLength          = null;
	
    
    this.updateArcLengths();
};

IKRS.CubicBezierCurve.prototype = new IKRS.Object();
IKRS.CubicBezierCurve.prototype.constructor = IKRS.CubicBezierCurve; 
    
    
IKRS.CubicBezierCurve.prototype.updateArcLengths = function() {
    var 
    //x1 = this.startPoint.x, 
    //y1 = this.startPoint.y, 
    //x2, y2,
    pointA = new THREE.Vector2( this.startPoint.x,
				this.startPoint.y
			      ),
    pointB = new THREE.Vector2( 0, 0 ),
    curveStep = 1.0/this.curveIntervals;
    
    var   u = curveStep; 

    // Clear segment cache
    this.segmentCache = [];
    // Push start point into buffer
    this.segmentCache.push( this.startPoint );
    
    this.segmentLengths = [];
    
    this.arcLength = 0.0;

    //var point;
    for( var i = 0; i < this.curveIntervals; i++) {
	
	pointB = this.getPointAt( (i+1) * curveStep );  // parameter is 'u' (not 't')
	
	
	// Store point into cache
	this.segmentCache.push( pointB ); // new THREE.Vector2(x2,y2) );

	// Calculate segment length
	//var tmpLength = Math.sqrt( Math.pow(x1-x2,2) + Math.pow(y1-y2,2) );
	var tmpLength = Math.sqrt( Math.pow(pointA.x-pointB.x,2) + Math.pow(pointA.y-pointB.y,2) );
	this.segmentLengths.push( tmpLength );
	this.arcLength += tmpLength;
	
        //x1 = point.x; // x2;
        //y1 = point.y; // y2;
	pointA = pointB;
        u += curveStep;
    } // END for


    // Check if there are enough segments so the max segment length is not bigger than 20px.
    // Each time the curce gets too long add more segments
    /* There's something going wrong
    if( this.arcLength/this.curveIntervals > 20 ) {

	//window.alert( "rescaling ..." );
	
	this.curveIntervals = this.arcLength / 20; 
	// recalculate (will only happen once)
	this.updateArcLengths();

    } else if( this.arcLength/this.curveIntervals < 10 ) {

	// But there should not be too many segments if the curve gets shorter
	this.curveIntervals = this.arcLength / 9; 
	// recalculate (will only happen once)
	this.updateArcLengths();

    }
    */

    //window.alert( "segmentCache=" + this.segmentCache + ", segmentLengths=" + this.segmentLengths + ", arcLength=" + this.arcLength );

}; // END function


IKRS.CubicBezierCurve.prototype.getStartPoint = function() {
    return this.startPoint;
};

IKRS.CubicBezierCurve.prototype.getEndPoint = function() {
    return this.endPoint;
};

IKRS.CubicBezierCurve.prototype.getStartControlPoint = function() {
    return this.startControlPoint;
};

IKRS.CubicBezierCurve.prototype.getEndControlPoint = function() {
    return this.endControlPoint;
};

IKRS.CubicBezierCurve.prototype.getPointAt = function( u ) {
    
    // Perform some powerful math magic
    var x = this.startPoint.x * Math.pow(1.0-u,3) + this.startControlPoint.x*3*u*Math.pow(1.0-u,2)
	+ this.endControlPoint.x*3*Math.pow(u,2)*(1.0-u)+this.endPoint.x*Math.pow(u,3);
    
    var y = this.startPoint.y*Math.pow(1.0-u,3)+this.startControlPoint.y*3*u*Math.pow(1.0-u,2)
	+ this.endControlPoint.y*3*Math.pow(u,2)*(1.0-u)+this.endPoint.y*Math.pow(u,3);
    
    return new THREE.Vector2( x, y );
};

IKRS.CubicBezierCurve.prototype.getPoint = function( t ) {  
    
    return this.getPointAt( t * this.arcLength );
};





                                                   

//window.alert( "IKRS.CubicBezierCurve=" +IKRS.CubicBezierCurve );
//window.alert( "IKRS.CubicBezierCurve.prototype=" + IKRS.CubicBezierCurve.prototype );