/*Math from "Making Thing Move!" by Keith Peters*/
public static function lineCircleIntersection(lineStart:Point, lineEnd:Point, entity:Entity):Boolean {
	var angle:Number = Math.atan2((lineEnd.y-lineStart.y), (lineEnd.x-lineStart.x));
	var dx:Number = entity.centerX-((lineStart.x+lineEnd.x) * 0.5);
	var dy:Number = entity.centerY-((lineStart.y+lineEnd.y) * 0.5);
	return (Math.abs(Math.cos(angle)*dy - Math.sin(angle)*dx) < entity.radius);
}

public static function distanceSq(lhs:Entity, rhs:Entity):Number{
	var dx:Number = lhs.centerX - rhs.centerX;
	var dy:Number = lhs.centerY - rhs.centerY;
	return (dx * dx + dy * dy);
}

public static function distance(lhs:Entity, rhs:Entity):Number{
	var dx:Number = lhs.centerX - rhs.centerX;
	var dy:Number = lhs.centerY - rhs.centerY;
	return Math.sqrt(dx * dx + dy * dy);
}

public static function intersectsAABB(lhs:core.Entity, rhs:core.Entity):Boolean {
	return !(lhs.right < rhs.left
			|| rhs.right < lhs.left
			|| lhs.bottom < rhs.top
			|| rhs.bottom < lhs.top);
}

//SAT intersection test. http://www.metanetsoftware.com/technique/tutorialA.html
//returns true on intersection, and sets the least intersecting axis in overlap
public static function getOverlap(lhs:Entity, rhs:Entity, overlap:Point):Boolean {
	overlap.setTo(0, 0);
	var centerDeltaX:Number = lhs.centerX - rhs.centerX;
	var halfWidths:Number = (lhs.width + rhs.width) * 0.5;

	if (Math.abs(centerDeltaX) > halfWidths) return false; //no overlap on x == no collision

	var centerDeltaY:Number = lhs.centerY - rhs.centerY;
	var halfHeights:Number = (lhs.height + rhs.height) * 0.5;

	if (Math.abs(centerDeltaY) > halfHeights) return false; //no overlap on y == no collision

	var dx:Number = halfWidths - Math.abs(centerDeltaX); //overlap on x
	var dy:Number = halfHeights - Math.abs(centerDeltaY); //overlap on y
	if (dy < dx) {
		overlap.y = (centerDeltaY < 0) ? -dy : dy;
	} else if (dy > dx) {
		overlap.x = (centerDeltaX < 0) ? -dx : dx;
	} else {
		overlap.x = (centerDeltaX < 0) ? -dx : dx;
		overlap.y = (centerDeltaY < 0) ? -dy : dy;
	}
	return true;
}