/**
 * Flade - Flash Dynamics Engine
 * Release 0.4 alpha 
 * AngularConstraint class
 * Copyright 2004, 2005 Alec Cove
 * 
 * This file is part of Flade. The Flash Dynamics Engine. 
 *	
 * Flade is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * Flade is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Flade; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Flash is a registered trademark of Macromedia
 */
 
 
AngularConstraint = function(pA, pB, pC) {
	
	this.pA = pA.curr;
	this.pB = pB.curr;
	this.pC = pC.curr;
		
	this.lineA = new Line(pA, pB);
	this.lineB = new Line(pB, pC);
		
	// lineC is the reference line for getting the angle of the line segments
	this.pD = new Vector(this.pB.x + 0, this.pB.y - 1);
	this.lineC = new Line(this.pB, this.pD);
		
	// theta to constrain to -- domain is -Math.PI to Math.PI
	this.targetTheta = this.calcTheta(this.pA, this.pB, this.pC);
	
	// coefficient of stiffness
	this.coeffStiff = 1;
}


AngularConstraint.prototype.resolve = function() {
	
	var center = this.getCentroid();
	
	// make sure the reference line position gets updated
	this.lineC.p2.x = this.lineC.p1.x + 0;
	this.lineC.p2.y = this.lineC.p1.y - 1;
	
	var abRadius = this.pA.distance(this.pB);
	var bcRadius = this.pB.distance(this.pC);
			
	var thetaABC = this.calcTheta(this.pA, this.pB, this.pC);
	var thetaABD = this.calcTheta(this.pA, this.pB, this.pD);
	var thetaCBD = this.calcTheta(this.pC, this.pB, this.pD);
	
	var halfTheta = (this.targetTheta - thetaABC) / 2;
	var paTheta = thetaABD + halfTheta * this.coeffStiff;
	var pcTheta = thetaCBD - halfTheta * this.coeffStiff;
	
	this.pA.x = abRadius * Math.sin(paTheta) + this.pB.x;
	this.pA.y = abRadius * Math.cos(paTheta) + this.pB.y;
	this.pC.x = bcRadius * Math.sin(pcTheta) + this.pB.x;
	this.pC.y = bcRadius * Math.cos(pcTheta) + this.pB.y;
	
	// move corrected angle to pre corrected center
	var newCenter = this.getCentroid();
	var dfx = newCenter.x - center.x;
	var dfy = newCenter.y - center.y;
	
	this.pA.x -= dfx; 
	this.pA.y -= dfy;
	this.pB.x -= dfx;  
	this.pB.y -= dfy;
	this.pC.x -= dfx;  
	this.pC.y -= dfy; 
}


AngularConstraint.prototype.calcTheta = function(pa, pb, pc) {
	
	var AB = new Vector(pb.x - pa.x, pb.y - pa.y);
	var BC = new Vector(pc.x - pb.x, pc.y - pb.y);
		
	var dotProd = AB.dot(BC);
	var crossProd = AB.cross(BC);
	return Math.atan2(crossProd, dotProd);
}


AngularConstraint.prototype.setTheta = function(t) {
	this.targetTheta = t;
}


AngularConstraint.prototype.getTheta = function(t) {
	return this.targetTheta;
}


AngularConstraint.prototype.paint = function() {	
	// do nothing (except just maintain the constraint interface)
}


AngularConstraint.prototype.getCentroid = function() {
	var avgX = (this.pA.x + this.pB.x + this.pC.x) / 3;
	var avgY = (this.pA.y + this.pB.y + this.pC.y) / 3;
	return new Vector(avgX, avgY);
}

// Line helper object 
Line = function(p1, p2) {
	this.p1 = p1;
	this.p2 = p2;
}