/**
 * Flade - Flash Dynamics Engine
 * Release 0.4 alpha 
 * Surface 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
 */

Surface = function(p1, p2) {
	
	this.p1 = p1;
	this.p2 = p2;
	
	this.isOrientH = true;
	this.normal = new Vector(0,0);
	this.calcNormal();
	
	// some precalculations
	this.rise = this.p2.y - this.p1.y;
	this.run = this.p2.x - this.p1.x;
	
	this.invRun = 1 / this.run;
	this.slope = this.rise / this.run;
	this.invB = 1 / (this.run * this.run + this.rise * this.rise);
	
	var drawClipName = "surfdrawclip_" + this.depth;
	this.dmc = createEmptyMovieClip (drawClipName, this.depth);
	this.dmc.lineStyle(0, 0x222288, 100);

	Surface.prototype.depth++;
}
Surface.prototype.depth = 2000;


Surface.prototype.setIsOrientH = function(isOrientH) {
	this.isOrientH = isOrientH;
}


Surface.prototype.calcNormal = function() {
	
	// find normal
	var dx = this.p2.x - this.p1.x;
	var dy = this.p2.y - this.p1.y;
	this.normal.x = dy 
	this.normal.y = -dx;
	
	// normalize
	var mag = Math.sqrt (
			(this.normal.x * this.normal.x) + 
			(this.normal.y * this.normal.y));
	this.normal.x /= mag;
	this.normal.y /= mag;
}


Surface.prototype.paint = function() {	
	Graphics.prototype.paintLine(this.dmc, this.p1.x, this.p1.y, this.p2.x, this.p2.y);
}


Surface.prototype.resolveWheelCollision = function(w, sysObj) {

	if (this.bounds(w.wp.curr, w.contactRadius)) {
		
		// get the closest point on the surface
		this.getClosestPoint(w.wp.curr, w.closestPoint);

		// get the normal of the circle relative to the location of the closest point
		var circleNormal = w.closestPoint.minusNew(w.wp.curr);
		circleNormal.normalize();
		
		/*
		 * if the center of the wheel has broken the ground plane
		 * keep the normal from 'flipping' to the opposite direction.
		 * for small wheels, this prevents break-throughs
		 */
		if (this.inequality(w.wp.curr)) {
			var absCX = Math.abs(circleNormal.x);
			circleNormal.x = (this.normal.x < 0) ? absCX : -absCX
			circleNormal.y = Math.abs(circleNormal.y);
		}
		
		// get contact point on edge of circle
		var contactPoint = w.wp.curr.plusNew(circleNormal.mult(w.wr));

		if (this.segmentInequality(contactPoint)) {

			// project back
			var dx = contactPoint.x - w.closestPoint.x;
			var dy = contactPoint.y - w.closestPoint.y;

			w.wp.curr.x -= dx;
			w.wp.curr.y -= dy;

			w.resolve(this.normal);
		}
	}
}


Surface.prototype.resolveParticleCollision = function(p, sysObj) {
	
	if (this.boundedSegmentInequality(p.curr)) {
		
		var vel = p.curr.minusNew(p.prev);
		var sDotV = this.normal.dot(vel);

		if (sDotV < 0) {
			// compute momentum of particle perpendicular to normal
			var velProjection = vel.minusNew(this.normal.multNew(sDotV));
			var perpMomentum = velProjection.multNew(sysObj.coeffFric);

			// compute momentum of particle in direction of normal
			var normMomentum = this.normal.multNew(sDotV * sysObj.coeffRest);
			var totalMomentum = normMomentum.plusNew(perpMomentum);
	
			// set new velocity w/ total momentum
			var newVel = vel.minusNew(totalMomentum);
			
			// project out of collision
			var mirrorPos = this.normal.dot(p.curr.minusNew(this.p1)) * sysObj.coeffRest;
			p.curr.minus(this.normal.multNew(mirrorPos));

			// apply new velocity
			p.prev = p.curr.minusNew(newVel);
		}
	}
}


Surface.prototype.segmentInequality = function(toPoint) {
	var u = this.findU(toPoint);
	var isUnder = this.inequality(toPoint);
	return (u >= 0 && u <= 1 && isUnder);
}


Surface.prototype.boundedSegmentInequality = function(toPoint) {
	
	var isBound;
	if (this.isOrientH) {
		isBound = ((toPoint.x >= this.p1.x) && (toPoint.x <= this.p2.x));
	} else if (this.p1.y < this.p2.y) {
		isBound = ((toPoint.y >= this.p1.y) && (toPoint.y <= this.p2.y));
	} else {
		isBound = ((toPoint.y <= this.p1.y) && (toPoint.y >= this.p2.y));
	}
	
	if (isBound) {
		return isUnder = this.inequality(toPoint);
	}
	return false;	
}


Surface.prototype.inequality = function(toPoint) {	
	// equation of a line
	var line = this.slope * (toPoint.x - this.p1.x) + (this.p1.y - toPoint.y);
	return (line <= 0);
}


Surface.prototype.bounds = function(toPoint, r) {	
	return ((toPoint.x >= this.p1.x - r) && (toPoint.x <= this.p2.x + r));
}



Surface.prototype.getClosestPoint = function(toPoint, returnVect) {
	
	var u = this.findU(toPoint);
	if (u <= 0) return this.p1;
	if (u >= 1) return this.p2;
	
	var x = this.p1.x + u * (this.p2.x - this.p1.x);
	var y = this.p1.y + u * (this.p2.y - this.p1.y);
	
	returnVect.x = x;
	returnVect.y = y;
}


Surface.prototype.findU = function (p) {
	var a = (p.x - this.p1.x) * this.run + (p.y - this.p1.y) * this.rise;
	return a * this.invB;
}