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

Wheel = function (x, y, r) {
	
	this.wr = r;						// wheel radius
	this.wp = new Particle(x, y); 		// wheel particle
	this.rp = new RimParticle(r, 2); 	// rim particle (radius, max torque)
	
	this.contactRadius = r;				// contact radius - for checking if in bounds of surface
										// by default its the radius, but for smaller wheels
										// its a good idea to set this larger than the radius
										
	this.coeffSlip = 0.0;				// 1 = totally slippery, 0 = full friction		
		
	this.closestPoint = new Vector(0,0);
	
	var drawClipName = "wheeldrawclip_" + this.depth;
	this.dmc = _root.createEmptyMovieClip(drawClipName, this.depth);
	Wheel.prototype.depth++;
}
Wheel.prototype.depth = 6000;


Wheel.prototype.verlet = function(sysObj) {
	this.rp.verlet(sysObj);
	this.wp.verlet(sysObj);
}
	

Wheel.prototype.checkCollision = function(surface, sysObj) {
	surface.resolveWheelCollision(this);
}


Wheel.prototype.paint = function() {
		
	// draw wheel circle
	var px = this.wp.curr.x;
	var py = this.wp.curr.y;
	var rx = this.rp.curr.x;
	var ry = this.rp.curr.y;
	
	this.dmc.clear();
	this.dmc.lineStyle(1, 0x222288, 100);
	Graphics.prototype.paintCircle(this.dmc, px, py, this.wr);
		
	// draw rim cross
	this.dmc.lineStyle(0, 0x999999, 100);
	Graphics.prototype.paintLine(this.dmc, rx + px, ry + py, px, py);
	Graphics.prototype.paintLine(this.dmc, -rx + px, -ry + py, px, py);
	Graphics.prototype.paintLine(this.dmc, -ry + px, rx + py, px, py);
	Graphics.prototype.paintLine(this.dmc, ry + px, -rx + py, px, py);
}


/*
 * simulates torque/wheel-gound interaction
 * n is the surface normal
 */
Wheel.prototype.resolve = function(n) {
		
	var wp = this.wp;
	var rp = this.rp;
	
	// this is the tangent vector at the rim particle
	var rx = -rp.curr.y;
	var ry = rp.curr.x;
	
	// normalize so we can scale by the rotational speed
	var len = Math.sqrt(rx * rx + ry * ry);
	rx /= len;
	ry /= len;
	
	// sx,sy is the velocity of the wheel's surface relative to the wheel
	var sx = rx * rp.speed;
	var sy = ry * rp.speed;
	
	// tx,ty is the velocity of the wheel relative to the world
	var tx = wp.curr.x - wp.prev.x;
	var ty = wp.curr.y - wp.prev.y;
	
	// vx,vy is the velocity of the wheel's surface relative to the ground
	var vx = tx + sx;
	var vy = ty + sy;
	
	// dp is the the wheel's surfacevel projected onto the ground's tangent
	var dp = -n.y * vx + n.x * vy;
	
	// set the wheel's spinspeed to track the ground
	rp.prev.x = rp.curr.x - dp * rx;
	rp.prev.y = rp.curr.y - dp * ry;
	
	// some of the wheel's torque is removed and converted into linear displacement
	var w0 = 1 - this.coeffSlip;
	wp.curr.x += w0 * rp.speed * -n.y;
	wp.curr.y += w0 * rp.speed * n.x;
	rp.speed *= this.coeffSlip;
}