/src/org/flixel/flixOld/org/flixel/FlxObject.as

package org.flixel
{
	import flash.display.Graphics;
	import flash.display.Sprite;
	import flash.geom.Point;
	
	import org.flixel.FlxBasic;
	
	/**
	 * This is the base class for most of the display objects (<code>FlxSprite</code>, <code>FlxText</code>, etc).
	 * It includes some basic attributes about game objects, including retro-style flickering,
	 * basic state information, sizes, scrolling, and basic physics and motion.
	 * 
	 * @author	Adam Atomic
	 */
	public class FlxObject extends FlxBasic
	{
		/**
		 * Generic value for "left" Used by <code>facing</code>, <code>allowCollisions</code>, and <code>touching</code>.
		 */
		static public const LEFT:uint	= 0x0001;
		/**
		 * Generic value for "right" Used by <code>facing</code>, <code>allowCollisions</code>, and <code>touching</code>.
		 */
		static public const RIGHT:uint	= 0x0010;
		/**
		 * Generic value for "up" Used by <code>facing</code>, <code>allowCollisions</code>, and <code>touching</code>.
		 */
		static public const UP:uint		= 0x0100;
		/**
		 * Generic value for "down" Used by <code>facing</code>, <code>allowCollisions</code>, and <code>touching</code>.
		 */
		static public const DOWN:uint	= 0x1000;
		
		/**
		 * Special-case constant meaning no collisions, used mainly by <code>allowCollisions</code> and <code>touching</code>.
		 */
		static public const NONE:uint	= 0;
		/**
		 * Special-case constant meaning up, used mainly by <code>allowCollisions</code> and <code>touching</code>.
		 */
		static public const CEILING:uint= UP;
		/**
		 * Special-case constant meaning down, used mainly by <code>allowCollisions</code> and <code>touching</code>.
		 */
		static public const FLOOR:uint	= DOWN;
		/**
		 * Special-case constant meaning only the left and right sides, used mainly by <code>allowCollisions</code> and <code>touching</code>.
		 */
		static public const WALL:uint	= LEFT | RIGHT;
		/**
		 * Special-case constant meaning any direction, used mainly by <code>allowCollisions</code> and <code>touching</code>.
		 */
		static public const ANY:uint	= LEFT | RIGHT | UP | DOWN;
		
		/**
		 * Handy constant used during collision resolution (see <code>separateX()</code> and <code>separateY()</code>).
		 */
		static public const OVERLAP_BIAS:Number = 4;
		
		/**
		 * Path behavior controls: move from the start of the path to the end then stop.
		 */
		static public const PATH_FORWARD:uint			= 0x000000;
		/**
		 * Path behavior controls: move from the end of the path to the start then stop.
		 */
		static public const PATH_BACKWARD:uint			= 0x000001;
		/**
		 * Path behavior controls: move from the start of the path to the end then directly back to the start, and start over.
		 */
		static public const PATH_LOOP_FORWARD:uint		= 0x000010;
		/**
		 * Path behavior controls: move from the end of the path to the start then directly back to the end, and start over.
		 */
		static public const PATH_LOOP_BACKWARD:uint		= 0x000100;
		/**
		 * Path behavior controls: move from the start of the path to the end then turn around and go back to the start, over and over.
		 */
		static public const PATH_YOYO:uint				= 0x001000;
		/**
		 * Path behavior controls: ignores any vertical component to the path data, only follows side to side.
		 */
		static public const PATH_HORIZONTAL_ONLY:uint	= 0x010000;
		/**
		 * Path behavior controls: ignores any horizontal component to the path data, only follows up and down.
		 */
		static public const PATH_VERTICAL_ONLY:uint		= 0x100000;
		
		/**
		 * X position of the upper left corner of this object in world space.
		 */
		public var x:Number;
		/**
		 * Y position of the upper left corner of this object in world space.
		 */
		public var y:Number;
		/**
		 * The width of this object.
		 */
		public var width:Number;
		/**
		 * The height of this object.
		 */
		public var height:Number;

		/**
		 * Whether an object will move/alter position after a collision.
		 */
		public var immovable:Boolean;
		
		/**
		 * The basic speed of this object.
		 */
		public var velocity:FlxPoint;
		/**
		 * The virtual mass of the object. Default value is 1.
		 * Currently only used with <code>elasticity</code> during collision resolution.
		 * Change at your own risk; effects seem crazy unpredictable so far!
		 */
		public var mass:Number;
		/**
		 * The bounciness of this object.  Only affects collisions.  Default value is 0, or "not bouncy at all."
		 */
		public var elasticity:Number;
		/**
		 * How fast the speed of this object is changing.
		 * Useful for smooth movement and gravity.
		 */
		public var acceleration:FlxPoint;
		/**
		 * This isn't drag exactly, more like deceleration that is only applied
		 * when acceleration is not affecting the sprite.
		 */
		public var drag:FlxPoint;
		/**
		 * If you are using <code>acceleration</code>, you can use <code>maxVelocity</code> with it
		 * to cap the speed automatically (very useful!).
		 */
		public var maxVelocity:FlxPoint;
		/**
		 * Set the angle of a sprite to rotate it.
		 * WARNING: rotating sprites decreases rendering
		 * performance for this sprite by a factor of 10x!
		 */
		public var angle:Number;
		/**
		 * This is how fast you want this sprite to spin.
		 */
		public var angularVelocity:Number;
		/**
		 * How fast the spin speed should change.
		 */
		public var angularAcceleration:Number;
		/**
		 * Like <code>drag</code> but for spinning.
		 */
		public var angularDrag:Number;
		/**
		 * Use in conjunction with <code>angularAcceleration</code> for fluid spin speed control.
		 */
		public var maxAngular:Number;
		/**
		 * Should always represent (0,0) - useful for different things, for avoiding unnecessary <code>new</code> calls.
		 */
		static protected const _pZero:FlxPoint = new FlxPoint();
		
		/**
		 * A point that can store numbers from 0 to 1 (for X and Y independently)
		 * that governs how much this object is affected by the camera subsystem.
		 * 0 means it never moves, like a HUD element or far background graphic.
		 * 1 means it scrolls along a the same speed as the foreground layer.
		 * scrollFactor is initialized as (1,1) by default.
		 */
		public var scrollFactor:FlxPoint;
		/**
		 * Internal helper used for retro-style flickering.
		 */
		protected var _flicker:Boolean;
		/**
		 * Internal helper used for retro-style flickering.
		 */
		protected var _flickerTimer:Number;
		/**
		 * Handy for storing health percentage or armor points or whatever.
		 */
		public var health:Number;
		/**
		 * This is just a pre-allocated x-y point container to be used however you like
		 */
		protected var _point:FlxPoint;
		/**
		 * This is just a pre-allocated rectangle container to be used however you like
		 */
		protected var _rect:FlxRect;
		/**
		 * Set this to false if you want to skip the automatic motion/movement stuff (see <code>updateMotion()</code>).
		 * FlxObject and FlxSprite default to true.
		 * FlxText, FlxTileblock, FlxTilemap and FlxSound default to false.
		 */
		public var moves:Boolean;
		/**
		 * Bit field of flags (use with UP, DOWN, LEFT, RIGHT, etc) indicating surface contacts.
		 * Use bitwise operators to check the values stored here, or use touching(), justStartedTouching(), etc.
		 * You can even use them broadly as boolean values if you're feeling saucy!
		 */
		public var touching:uint;
		/**
		 * Bit field of flags (use with UP, DOWN, LEFT, RIGHT, etc) indicating surface contacts from the previous game loop step.
		 * Use bitwise operators to check the values stored here, or use touching(), justStartedTouching(), etc.
		 * You can even use them broadly as boolean values if you're feeling saucy!
		 */
		public var wasTouching:uint;
		/**
		 * Bit field of flags (use with UP, DOWN, LEFT, RIGHT, etc) indicating collision directions.
		 * Use bitwise operators to check the values stored here.
		 * Useful for things like one-way platforms (e.g. allowCollisions = UP;)
		 * The accessor "solid" just flips this variable between NONE and ANY.
		 */
		public var allowCollisions:uint;
		
		/**
		 * Important variable for collision processing.
		 * By default this value is set automatically during <code>preUpdate()</code>.
		 */
		public var last:FlxPoint;
		
		/**
		 * A reference to a path object.  Null by default, assigned by <code>followPath()</code>.
		 */
		public var path:FlxPath;
		/**
		 * The speed at which the object is moving on the path.
		 * When an object completes a non-looping path circuit,
		 * the pathSpeed will be zeroed out, but the <code>path</code> reference
		 * will NOT be nulled out.  So <code>pathSpeed</code> is a good way
		 * to check if this object is currently following a path or not.
		 */
		public var pathSpeed:Number;
		/**
		 * The angle in degrees between this object and the next node, where 0 is directly upward, and 90 is to the right.
		 */
		public var pathAngle:Number;
		/**
		 * Internal helper, tracks which node of the path this object is moving toward.
		 */
		protected var _pathNodeIndex:int;
		/**
		 * Internal tracker for path behavior flags (like looping, horizontal only, etc).
		 */
		protected var _pathMode:uint;
		/**
		 * Internal helper for node navigation, specifically yo-yo and backwards movement.
		 */
		protected var _pathInc:int;
		/**
		 * Internal flag for whether hte object's angle should be adjusted to the path angle during path follow behavior.
		 */
		protected var _pathRotate:Boolean;
		
		/**
		 * Instantiates a <code>FlxObject</code>.
		 * 
		 * @param	X		The X-coordinate of the point in space.
		 * @param	Y		The Y-coordinate of the point in space.
		 * @param	Width	Desired width of the rectangle.
		 * @param	Height	Desired height of the rectangle.
		 */
		public function FlxObject(X:Number=0,Y:Number=0,Width:Number=0,Height:Number=0)
		{
			x = X;
			y = Y;
			last = new FlxPoint(x,y);
			width = Width;
			height = Height;
			mass = 1.0;
			elasticity = 0.0;

			immovable = false;
			moves = true;
			
			touching = NONE;
			wasTouching = NONE;
			allowCollisions = ANY;
			
			velocity = new FlxPoint();
			acceleration = new FlxPoint();
			drag = new FlxPoint();
			maxVelocity = new FlxPoint(10000,10000);
			
			angle = 0;
			angularVelocity = 0;
			angularAcceleration = 0;
			angularDrag = 0;
			maxAngular = 10000;
			
			scrollFactor = new FlxPoint(1.0,1.0);
			_flicker = false;
			_flickerTimer = 0;
			
			_point = new FlxPoint();
			_rect = new FlxRect();
			
			path = null;
			pathSpeed = 0;
			pathAngle = 0;
		}
		
		/**
		 * Override this function to null out variables or
		 * manually call destroy() on class members if necessary.
		 * Don't forget to call super.destroy()!
		 */
		override public function destroy():void
		{
			velocity = null;
			acceleration = null;
			drag = null;
			maxVelocity = null;
			scrollFactor = null;
			_point = null;
			_rect = null;
			last = null;
			cameras = null;
			if(path != null)
				path.destroy();
			path = null;
		}
		
		/**
		 * Pre-update is called right before <code>update()</code> on each object in the game loop.
		 * In <code>FlxObject</code> it controls the flicker timer,
		 * tracking the last coordinates for collision purposes,
		 * and checking if the object is moving along a path or not.
		 */
		override public function preUpdate():void
		{
			_ACTIVECOUNT++;
			
			if(_flickerTimer != 0)
			{
				if(_flickerTimer > 0)
				{
					_flickerTimer = _flickerTimer - FlxG.elapsed;
					if(_flickerTimer <= 0)
					{
						_flickerTimer = 0;
						_flicker = false;
					}
				}
			}
			
			last.x = x;
			last.y = y;
			
			if((path != null) && (pathSpeed != 0) && (path.nodes[_pathNodeIndex] != null))
				updatePathMotion();
		}
		
		/**
		 * Post-update is called right after <code>update()</code> on each object in the game loop.
		 * In <code>FlxObject</code> this function handles integrating the objects motion
		 * based on the velocity and acceleration settings, and tracking/clearing the <code>touching</code> flags.
		 */
		override public function postUpdate():void
		{
			if(moves)
				updateMotion();
			
			wasTouching = touching;
			touching = NONE;
		}
		
		/**
		 * Internal function for updating the position and speed of this object.
		 * Useful for cases when you need to update this but are buried down in too many supers.
		 * Does a slightly fancier-than-normal integration to help with higher fidelity framerate-independenct motion.
		 */
		protected function updateMotion():void
		{
			var delta:Number;
			var velocityDelta:Number;

			velocityDelta = (FlxU.computeVelocity(angularVelocity,angularAcceleration,angularDrag,maxAngular) - angularVelocity)/2;
			angularVelocity += velocityDelta; 
			angle += angularVelocity*FlxG.elapsed;
			angularVelocity += velocityDelta;
			
			velocityDelta = (FlxU.computeVelocity(velocity.x,acceleration.x,drag.x,maxVelocity.x) - velocity.x)/2;
			velocity.x += velocityDelta;
			delta = velocity.x*FlxG.elapsed;
			velocity.x += velocityDelta;
			x += delta;
			
			velocityDelta = (FlxU.computeVelocity(velocity.y,acceleration.y,drag.y,maxVelocity.y) - velocity.y)/2;
			velocity.y += velocityDelta;
			delta = velocity.y*FlxG.elapsed;
			velocity.y += velocityDelta;
			y += delta;
		}
		
		/**
		 * Rarely called, and in this case just increments the visible objects count and calls <code>drawDebug()</code> if necessary.
		 */
		override public function draw():void
		{
			if(cameras == null)
				cameras = FlxG.cameras;
			var camera:FlxCamera;
			var i:uint = 0;
			var l:uint = cameras.length;
			while(i < l)
			{
				camera = cameras[i++];
				if(!onScreen(camera))
					continue;
				_VISIBLECOUNT++;
				if(FlxG.visualDebug && !ignoreDrawDebug)
					drawDebug(camera);
			}
		}
		
		/**
		 * Override this function to draw custom "debug mode" graphics to the
		 * specified camera while the debugger's visual mode is toggled on.
		 * 
		 * @param	Camera	Which camera to draw the debug visuals to.
		 */
		override public function drawDebug(Camera:FlxCamera=null):void
		{
			if(Camera == null)
				Camera = FlxG.camera;

			//get bounding box coordinates
			var boundingBoxX:Number = x - int(Camera.scroll.x*scrollFactor.x); //copied from getScreenXY()
			var boundingBoxY:Number = y - int(Camera.scroll.y*scrollFactor.y);
			boundingBoxX = int(boundingBoxX + ((boundingBoxX > 0)?0.0000001:-0.0000001));
			boundingBoxY = int(boundingBoxY + ((boundingBoxY > 0)?0.0000001:-0.0000001));
			var boundingBoxWidth:int = (width != int(width))?width:width-1;
			var boundingBoxHeight:int = (height != int(height))?height:height-1;

			//fill static graphics object with square shape
			var gfx:Graphics = FlxG.flashGfx;
			gfx.clear();
			gfx.moveTo(boundingBoxX,boundingBoxY);
			var boundingBoxColor:uint;
			if(allowCollisions)
			{
				if(allowCollisions != ANY)
					boundingBoxColor = FlxG.PINK;
				if(immovable)
					boundingBoxColor = FlxG.GREEN;
				else
					boundingBoxColor = FlxG.RED;
			}
			else
				boundingBoxColor = FlxG.BLUE;
			gfx.lineStyle(1,boundingBoxColor,0.5);
			gfx.lineTo(boundingBoxX+boundingBoxWidth,boundingBoxY);
			gfx.lineTo(boundingBoxX+boundingBoxWidth,boundingBoxY+boundingBoxHeight);
			gfx.lineTo(boundingBoxX,boundingBoxY+boundingBoxHeight);
			gfx.lineTo(boundingBoxX,boundingBoxY);
			
			//draw graphics shape to camera buffer
			Camera.buffer.draw(FlxG.flashGfxSprite);
		}
		
		/**
		 * Call this function to give this object a path to follow.
		 * If the path does not have at least one node in it, this function
		 * will log a warning message and return.
		 * 
		 * @param	Path		The <code>FlxPath</code> you want this object to follow.
		 * @param	Speed		How fast to travel along the path in pixels per second.
		 * @param	Mode		Optional, controls the behavior of the object following the path using the path behavior constants.  Can use multiple flags at once, for example PATH_YOYO|PATH_HORIZONTAL_ONLY will make an object move back and forth along the X axis of the path only.
		 * @param	AutoRotate	Automatically point the object toward the next node.  Assumes the graphic is pointing upward.  Default behavior is false, or no automatic rotation.
		 */
		public function followPath(Path:FlxPath,Speed:Number=100,Mode:uint=PATH_FORWARD,AutoRotate:Boolean=false):void
		{
			if(Path.nodes.length <= 0)
			{
				FlxG.log("WARNING: Paths need at least one node in them to be followed.");
				return;
			}
			
			path = Path;
			pathSpeed = FlxU.abs(Speed);
			_pathMode = Mode;
			_pathRotate = AutoRotate;
			
			//get starting node
			if((_pathMode == PATH_BACKWARD) || (_pathMode == PATH_LOOP_BACKWARD))
			{
				_pathNodeIndex = path.nodes.length-1;
				_pathInc = -1;
			}
			else
			{
				_pathNodeIndex = 0;
				_pathInc = 1;
			}
		}
		
		/**
		 * Tells this object to stop following the path its on.
		 * 
		 * @param	DestroyPath		Tells this function whether to call destroy on the path object.  Default value is false.
		 */
		public function stopFollowingPath(DestroyPath:Boolean=false):void
		{
			pathSpeed = 0;
			if(DestroyPath && (path != null))
			{
				path.destroy();
				path = null;
			}
		}
		
		/**
		 * Internal function that decides what node in the path to aim for next based on the behavior flags.
		 * 
		 * @return	The node (a <code>FlxPoint</code> object) we are aiming for next.
		 */
		protected function advancePath(Snap:Boolean=true):FlxPoint
		{
			if(Snap)
			{
				var oldNode:FlxPoint = path.nodes[_pathNodeIndex];
				if(oldNode != null)
				{
					if((_pathMode & PATH_VERTICAL_ONLY) == 0)
						x = oldNode.x - width*0.5;
					if((_pathMode & PATH_HORIZONTAL_ONLY) == 0)
						y = oldNode.y - height*0.5;
				}
			}
			
			_pathNodeIndex += _pathInc;
			
			if((_pathMode & PATH_BACKWARD) > 0)
			{
				if(_pathNodeIndex < 0)
				{
					_pathNodeIndex = 0;
					pathSpeed = 0;
				}
			}
			else if((_pathMode & PATH_LOOP_FORWARD) > 0)
			{
				if(_pathNodeIndex >= path.nodes.length)
					_pathNodeIndex = 0;
			}
			else if((_pathMode & PATH_LOOP_BACKWARD) > 0)
			{
				if(_pathNodeIndex < 0)
				{
					_pathNodeIndex = path.nodes.length-1;
					if(_pathNodeIndex < 0)
						_pathNodeIndex = 0;
				}
			}
			else if((_pathMode & PATH_YOYO) > 0)
			{
				if(_pathInc > 0)
				{
					if(_pathNodeIndex >= path.nodes.length)
					{
						_pathNodeIndex = path.nodes.length-2;
						if(_pathNodeIndex < 0)
							_pathNodeIndex = 0;
						_pathInc = -_pathInc;
					}
				}
				else if(_pathNodeIndex < 0)
				{
					_pathNodeIndex = 1;
					if(_pathNodeIndex >= path.nodes.length)
						_pathNodeIndex = path.nodes.length-1;
					if(_pathNodeIndex < 0)
						_pathNodeIndex = 0;
					_pathInc = -_pathInc;
				}
			}
			else
			{
				if(_pathNodeIndex >= path.nodes.length)
				{
					_pathNodeIndex = path.nodes.length-1;
					pathSpeed = 0;
				}
			}

			return path.nodes[_pathNodeIndex];
		}
		
		/**
		 * Internal function for moving the object along the path.
		 * Generally this function is called automatically by <code>preUpdate()</code>.
		 * The first half of the function decides if the object can advance to the next node in the path,
		 * while the second half handles actually picking a velocity toward the next node.
		 */
		protected function updatePathMotion():void
		{
			//first check if we need to be pointing at the next node yet
			_point.x = x + width*0.5;
			_point.y = y + height*0.5;
			var node:FlxPoint = path.nodes[_pathNodeIndex];
			var deltaX:Number = node.x - _point.x;
			var deltaY:Number = node.y - _point.y;
			
			var horizontalOnly:Boolean = (_pathMode & PATH_HORIZONTAL_ONLY) > 0;
			var verticalOnly:Boolean = (_pathMode & PATH_VERTICAL_ONLY) > 0;
			
			if(horizontalOnly)
			{
				if(((deltaX>0)?deltaX:-deltaX) < pathSpeed*FlxG.elapsed)
					node = advancePath();
			}
			else if(verticalOnly)
			{
				if(((deltaY>0)?deltaY:-deltaY) < pathSpeed*FlxG.elapsed)
					node = advancePath();
			}
			else
			{
				if(Math.sqrt(deltaX*deltaX + deltaY*deltaY) < pathSpeed*FlxG.elapsed)
					node = advancePath();
			}
			
			//then just move toward the current node at the requested speed
			if(pathSpeed != 0)
			{
				//set velocity based on path mode
				_point.x = x + width*0.5;
				_point.y = y + height*0.5;
				if(horizontalOnly || (_point.y == node.y))
				{
					velocity.x = (_point.x < node.x)?pathSpeed:-pathSpeed;
					if(velocity.x < 0)
						pathAngle = -90;
					else
						pathAngle = 90;
					if(!horizontalOnly)
						velocity.y = 0;
				}
				else if(verticalOnly || (_point.x == node.x))
				{
					velocity.y = (_point.y < node.y)?pathSpeed:-pathSpeed;
					if(velocity.y < 0)
						pathAngle = 0;
					else
						pathAngle = 180;
					if(!verticalOnly)
						velocity.x = 0;
				}
				else
				{
					pathAngle = FlxU.getAngle(_point,node);
					FlxU.rotatePoint(0,pathSpeed,0,0,pathAngle,velocity);
				}
				
				//then set object rotation if necessary
				if(_pathRotate)
				{
					angularVelocity = 0;
					angularAcceleration = 0;
					angle = pathAngle;
				}
			}			
		}
		
		/**
		 * Checks to see if some <code>FlxObject</code> overlaps this <code>FlxObject</code> or <code>FlxGroup</code>.
		 * If the group has a LOT of things in it, it might be faster to use <code>FlxG.overlaps()</code>.
		 * WARNING: Currently tilemaps do NOT support screen space overlap checks!
		 * 
		 * @param	ObjectOrGroup	The object or group being tested.
		 * @param	InScreenSpace	Whether to take scroll factors into account when checking for overlap.  Default is false, or "only compare in world space."
		 * @param	Camera			Specify which game camera you want.  If null getScreenXY() will just grab the first global camera.
		 * 
		 * @return	Whether or not the two objects overlap.
		 */
		public function overlaps(ObjectOrGroup:FlxBasic,InScreenSpace:Boolean=false,Camera:FlxCamera=null):Boolean
		{
			if(ObjectOrGroup is FlxGroup)
			{
				var results:Boolean = false;
				var i:uint = 0;
				var members:Array = (ObjectOrGroup as FlxGroup).members;
				while(i < length)
				{
					if(overlaps(members[i++],InScreenSpace,Camera))
						results = true;
				}
				return results;
			}
			
			if(ObjectOrGroup is FlxTilemap)
			{
				//Since tilemap's have to be the caller, not the target, to do proper tile-based collisions,
				// we redirect the call to the tilemap overlap here.
				return (ObjectOrGroup as FlxTilemap).overlaps(this,InScreenSpace,Camera);
			}
			
			var object:FlxObject = ObjectOrGroup as FlxObject;
			if(!InScreenSpace)
			{
				return	(object.x + object.width > x) && (object.x < x + width) &&
						(object.y + object.height > y) && (object.y < y + height);
			}

			if(Camera == null)
				Camera = FlxG.camera;
			var objectScreenPos:FlxPoint = object.getScreenXY(null,Camera);
			getScreenXY(_point,Camera);
			return	(objectScreenPos.x + object.width > _point.x) && (objectScreenPos.x < _point.x + width) &&
					(objectScreenPos.y + object.height > _point.y) && (objectScreenPos.y < _point.y + height);
		}
		
		/**
		 * Checks to see if this <code>FlxObject</code> were located at the given position, would it overlap the <code>FlxObject</code> or <code>FlxGroup</code>?
		 * This is distinct from overlapsPoint(), which just checks that point, rather than taking the object's size into account.
		 * WARNING: Currently tilemaps do NOT support screen space overlap checks!
		 * 
		 * @param	X				The X position you want to check.  Pretends this object (the caller, not the parameter) is located here.
		 * @param	Y				The Y position you want to check.  Pretends this object (the caller, not the parameter) is located here.
		 * @param	ObjectOrGroup	The object or group being tested.
		 * @param	InScreenSpace	Whether to take scroll factors into account when checking for overlap.  Default is false, or "only compare in world space."
		 * @param	Camera			Specify which game camera you want.  If null getScreenXY() will just grab the first global camera.
		 * 
		 * @return	Whether or not the two objects overlap.
		 */
		public function overlapsAt(X:Number,Y:Number,ObjectOrGroup:FlxBasic,InScreenSpace:Boolean=false,Camera:FlxCamera=null):Boolean
		{
			if(ObjectOrGroup is FlxGroup)
			{
				var results:Boolean = false;
				var basic:FlxBasic;
				var i:uint = 0;
				var members:Array = (ObjectOrGroup as FlxGroup).members;
				while(i < length)
				{
					if(overlapsAt(X,Y,members[i++],InScreenSpace,Camera))
						results = true;
				}
				return results;
			}
			
			if(ObjectOrGroup is FlxTilemap)
			{
				//Since tilemap's have to be the caller, not the target, to do proper tile-based collisions,
				// we redirect the call to the tilemap overlap here.
				//However, since this is overlapsAt(), we also have to invent the appropriate position for the tilemap.
				//So we calculate the offset between the player and the requested position, and subtract that from the tilemap.
				var tilemap:FlxTilemap = ObjectOrGroup as FlxTilemap;
				return tilemap.overlapsAt(tilemap.x - (X - x),tilemap.y - (Y - y),this,InScreenSpace,Camera);
			}
			
			var object:FlxObject = ObjectOrGroup as FlxObject;
			if(!InScreenSpace)
			{
				return	(object.x + object.width > X) && (object.x < X + width) &&
						(object.y + object.height > Y) && (object.y < Y + height);
			}
			
			if(Camera == null)
				Camera = FlxG.camera;
			var objectScreenPos:FlxPoint = object.getScreenXY(null,Camera);
			_point.x = X - int(Camera.scroll.x*scrollFactor.x); //copied from getScreenXY()
			_point.y = Y - int(Camera.scroll.y*scrollFactor.y);
			_point.x += (_point.x > 0)?0.0000001:-0.0000001;
			_point.y += (_point.y > 0)?0.0000001:-0.0000001;
			return	(objectScreenPos.x + object.width > _point.x) && (objectScreenPos.x < _point.x + width) &&
				(objectScreenPos.y + object.height > _point.y) && (objectScreenPos.y < _point.y + height);
		}
		
		/**
		 * Checks to see if a point in 2D world space overlaps this <code>FlxObject</code> object.
		 * 
		 * @param	Point			The point in world space you want to check.
		 * @param	InScreenSpace	Whether to take scroll factors into account when checking for overlap.
		 * @param	Camera			Specify which game camera you want.  If null getScreenXY() will just grab the first global camera.
		 * 
		 * @return	Whether or not the point overlaps this object.
		 */
		public function overlapsPoint(Point:FlxPoint,InScreenSpace:Boolean=false,Camera:FlxCamera=null):Boolean
		{
			if(!InScreenSpace)
				return (Point.x > x) && (Point.x < x + width) && (Point.y > y) && (Point.y < y + height);

			if(Camera == null)
				Camera = FlxG.camera;
			var X:Number = Point.x - Camera.scroll.x;
			var Y:Number = Point.y - Camera.scroll.y;
			getScreenXY(_point,Camera);
			return (X > _point.x) && (X < _point.x+width) && (Y > _point.y) && (Y < _point.y+height);
		}
		
		/**
		 * Check and see if this object is currently on screen.
		 * 
		 * @param	Camera		Specify which game camera you want.  If null getScreenXY() will just grab the first global camera.
		 * 
		 * @return	Whether the object is on screen or not.
		 */
		public function onScreen(Camera:FlxCamera=null):Boolean
		{
			if(Camera == null)
				Camera = FlxG.camera;
			getScreenXY(_point,Camera);
			return (_point.x + width > 0) && (_point.x < Camera.width) && (_point.y + height > 0) && (_point.y < Camera.height);
		}
		
		/**
		 * Call this function to figure out the on-screen position of the object.
		 * 
		 * @param	Camera		Specify which game camera you want.  If null getScreenXY() will just grab the first global camera.
		 * @param	Point		Takes a <code>FlxPoint</code> object and assigns the post-scrolled X and Y values of this object to it.
		 * 
		 * @return	The <code>Point</code> you passed in, or a new <code>Point</code> if you didn't pass one, containing the screen X and Y position of this object.
		 */
		public function getScreenXY(Point:FlxPoint=null,Camera:FlxCamera=null):FlxPoint
		{
			if(Point == null)
				Point = new FlxPoint();
			if(Camera == null)
				Camera = FlxG.camera;
			Point.x = x - int(Camera.scroll.x*scrollFactor.x);
			Point.y = y - int(Camera.scroll.y*scrollFactor.y);
			Point.x += (Point.x > 0)?0.0000001:-0.0000001;
			Point.y += (Point.y > 0)?0.0000001:-0.0000001;
			return Point;
		}
		
		/**
		 * Tells this object to flicker, retro-style.
		 * Pass a negative value to flicker forever.
		 * 
		 * @param	Duration	How many seconds to flicker for.
		 */
		public function flicker(Duration:Number=1):void
		{
			_flickerTimer = Duration;
			if(_flickerTimer == 0)
				_flicker = false;
		}
		
		/**
		 * Check to see if the object is still flickering.
		 * 
		 * @return	Whether the object is flickering or not.
		 */
		public function get flickering():Boolean
		{
			return _flickerTimer != 0;
		}
		
		/**
		 * Whether the object collides or not.  For more control over what directions
		 * the object will collide from, use collision constants (like LEFT, FLOOR, etc)
		 * to set the value of allowCollisions directly.
		 */
		public function get solid():Boolean
		{
			return (allowCollisions & ANY) > NONE;
		}
		
		/**
		 * @private
		 */
		public function set solid(Solid:Boolean):void
		{
			if(Solid)
				allowCollisions = ANY;
			else
				allowCollisions = NONE;
		}
		
		/**
		 * Retrieve the midpoint of this object in world coordinates.
		 * 
		 * @Point	Allows you to pass in an existing <code>FlxPoint</code> object if you're so inclined.  Otherwise a new one is created.
		 * 
		 * @return	A <code>FlxPoint</code> object containing the midpoint of this object in world coordinates.
		 */
		public function getMidpoint(Point:FlxPoint=null):FlxPoint
		{
			if(Point == null)
				Point = new FlxPoint();
			Point.x = x + width*0.5;
			Point.y = y + height*0.5;
			return Point;
		}
		
		/**
		 * Handy function for reviving game objects.
		 * Resets their existence flags and position.
		 * 
		 * @param	X	The new X position of this object.
		 * @param	Y	The new Y position of this object.
		 */
		public function reset(X:Number,Y:Number):void
		{
			revive();
			touching = NONE;
			wasTouching = NONE;
			x = X;
			y = Y;
			last.x = x;
			last.y = y;
			velocity.x = 0;
			velocity.y = 0;
		}
		
		/**
		 * Handy function for checking if this object is touching a particular surface.
		 * For slightly better performance you can just &amp; the value directly into <code>touching</code>.
		 * However, this method is good for readability and accessibility.
		 * 
		 * @param	Direction	Any of the collision flags (e.g. LEFT, FLOOR, etc).
		 * 
		 * @return	Whether the object is touching an object in (any of) the specified direction(s) this frame.
		 */
		public function isTouching(Direction:uint):Boolean
		{
			return (touching & Direction) > NONE;
		}
		
		/**
		 * Handy function for checking if this object is just landed on a particular surface.
		 * 
		 * @param	Direction	Any of the collision flags (e.g. LEFT, FLOOR, etc).
		 * 
		 * @return	Whether the object just landed on (any of) the specified surface(s) this frame.
		 */
		public function justTouched(Direction:uint):Boolean
		{
			return ((touching & Direction) > NONE) && ((wasTouching & Direction) <= NONE);
		}
		
		/**
		 * Reduces the "health" variable of this sprite by the amount specified in Damage.
		 * Calls kill() if health drops to or below zero.
		 * 
		 * @param	Damage		How much health to take away (use a negative number to give a health bonus).
		 */
		public function hurt(Damage:Number):void
		{
			health = health - Damage;
			if(health <= 0)
				kill();
		}
		
		/**
		 * The main collision resolution function in flixel.
		 * 
		 * @param	Object1 	Any <code>FlxObject</code>.
		 * @param	Object2		Any other <code>FlxObject</code>.
		 * 
		 * @return	Whether the objects in fact touched and were separated.
		 */
		static public function separate(Object1:FlxObject, Object2:FlxObject):Boolean
		{
			var separatedX:Boolean = separateX(Object1,Object2);
			var separatedY:Boolean = separateY(Object1,Object2);
			return separatedX || separatedY;
		}
		
		/**
		 * The X-axis component of the object separation process.
		 * 
		 * @param	Object1 	Any <code>FlxObject</code>.
		 * @param	Object2		Any other <code>FlxObject</code>.
		 * 
		 * @return	Whether the objects in fact touched and were separated along the X axis.
		 */
		static public function separateX(Object1:FlxObject, Object2:FlxObject):Boolean
		{
			//can't separate two immovable objects
			var obj1immovable:Boolean = Object1.immovable;
			var obj2immovable:Boolean = Object2.immovable;
			if(obj1immovable && obj2immovable)
				return false;
			
			//If one of the objects is a tilemap, just pass it off.
			if(Object1 is FlxTilemap)
				return (Object1 as FlxTilemap).overlapsWithCallback(Object2,separateX);
			if(Object2 is FlxTilemap)
				return (Object2 as FlxTilemap).overlapsWithCallback(Object1,separateX,true);
			
			//First, get the two object deltas
			var overlap:Number = 0;
			var obj1delta:Number = Object1.x - Object1.last.x;
			var obj2delta:Number = Object2.x - Object2.last.x;
			if(obj1delta != obj2delta)
			{
				//Check if the X hulls actually overlap
				var obj1deltaAbs:Number = (obj1delta > 0)?obj1delta:-obj1delta;
				var obj2deltaAbs:Number = (obj2delta > 0)?obj2delta:-obj2delta;
				var obj1rect:FlxRect = new FlxRect(Object1.x-((obj1delta > 0)?obj1delta:0),Object1.last.y,Object1.width+((obj1delta > 0)?obj1delta:-obj1delta),Object1.height);
				var obj2rect:FlxRect = new FlxRect(Object2.x-((obj2delta > 0)?obj2delta:0),Object2.last.y,Object2.width+((obj2delta > 0)?obj2delta:-obj2delta),Object2.height);
				if((obj1rect.x + obj1rect.width > obj2rect.x) && (obj1rect.x < obj2rect.x + obj2rect.width) && (obj1rect.y + obj1rect.height > obj2rect.y) && (obj1rect.y < obj2rect.y + obj2rect.height))
				{
					var maxOverlap:Number = obj1deltaAbs + obj2deltaAbs + OVERLAP_BIAS;
					
					//If they did overlap (and can), figure out by how much and flip the corresponding flags
					if(obj1delta > obj2delta)
					{
						overlap = Object1.x + Object1.width - Object2.x;
						if((overlap > maxOverlap) || !(Object1.allowCollisions & RIGHT) || !(Object2.allowCollisions & LEFT))
							overlap = 0;
						else
						{
							Object1.touching |= RIGHT;
							Object2.touching |= LEFT;
						}
					}
					else if(obj1delta < obj2delta)
					{
						overlap = Object1.x - Object2.width - Object2.x;
						if((-overlap > maxOverlap) || !(Object1.allowCollisions & LEFT) || !(Object2.allowCollisions & RIGHT))
							overlap = 0;
						else
						{
							Object1.touching |= LEFT;
							Object2.touching |= RIGHT;
						}
					}
				}
			}
			
			//Then adjust their positions and velocities accordingly (if there was any overlap)
			if(overlap != 0)
			{
				var obj1v:Number = Object1.velocity.x;
				var obj2v:Number = Object2.velocity.x;
				
				if(!obj1immovable && !obj2immovable)
				{
					overlap *= 0.5;
					Object1.x = Object1.x - overlap;
					Object2.x += overlap;

					var obj1velocity:Number = Math.sqrt((obj2v * obj2v * Object2.mass)/Object1.mass) * ((obj2v > 0)?1:-1);
					var obj2velocity:Number = Math.sqrt((obj1v * obj1v * Object1.mass)/Object2.mass) * ((obj1v > 0)?1:-1);
					var average:Number = (obj1velocity + obj2velocity)*0.5;
					obj1velocity -= average;
					obj2velocity -= average;
					Object1.velocity.x = average + obj1velocity * Object1.elasticity;
					Object2.velocity.x = average + obj2velocity * Object2.elasticity;
				}
				else if(!obj1immovable)
				{
					Object1.x = Object1.x - overlap;
					Object1.velocity.x = obj2v - obj1v*Object1.elasticity;
				}
				else if(!obj2immovable)
				{
					Object2.x += overlap;
					Object2.velocity.x = obj1v - obj2v*Object2.elasticity;
				}
				return true;
			}
			else
				return false;
		}
		
		/**
		 * The Y-axis component of the object separation process.
		 * 
		 * @param	Object1 	Any <code>FlxObject</code>.
		 * @param	Object2		Any other <code>FlxObject</code>.
		 * 
		 * @return	Whether the objects in fact touched and were separated along the Y axis.
		 */
		static public function separateY(Object1:FlxObject, Object2:FlxObject):Boolean
		{
			//can't separate two immovable objects
			var obj1immovable:Boolean = Object1.immovable;
			var obj2immovable:Boolean = Object2.immovable;
			if(obj1immovable && obj2immovable)
				return false;
			
			//If one of the objects is a tilemap, just pass it off.
			if(Object1 is FlxTilemap)
				return (Object1 as FlxTilemap).overlapsWithCallback(Object2,separateY);
			if(Object2 is FlxTilemap)
				return (Object2 as FlxTilemap).overlapsWithCallback(Object1,separateY,true);

			//First, get the two object deltas
			var overlap:Number = 0;
			var obj1delta:Number = Object1.y - Object1.last.y;
			var obj2delta:Number = Object2.y - Object2.last.y;
			if(obj1delta != obj2delta)
			{
				//Check if the Y hulls actually overlap
				var obj1deltaAbs:Number = (obj1delta > 0)?obj1delta:-obj1delta;
				var obj2deltaAbs:Number = (obj2delta > 0)?obj2delta:-obj2delta;
				var obj1rect:FlxRect = new FlxRect(Object1.x,Object1.y-((obj1delta > 0)?obj1delta:0),Object1.width,Object1.height+obj1deltaAbs);
				var obj2rect:FlxRect = new FlxRect(Object2.x,Object2.y-((obj2delta > 0)?obj2delta:0),Object2.width,Object2.height+obj2deltaAbs);
				if((obj1rect.x + obj1rect.width > obj2rect.x) && (obj1rect.x < obj2rect.x + obj2rect.width) && (obj1rect.y + obj1rect.height > obj2rect.y) && (obj1rect.y < obj2rect.y + obj2rect.height))
				{
					var maxOverlap:Number = obj1deltaAbs + obj2deltaAbs + OVERLAP_BIAS;
					
					//If they did overlap (and can), figure out by how much and flip the corresponding flags
					if(obj1delta > obj2delta)
					{
						overlap = Object1.y + Object1.height - Object2.y;
						if((overlap > maxOverlap) || !(Object1.allowCollisions & DOWN) || !(Object2.allowCollisions & UP))
							overlap = 0;
						else
						{
							Object1.touching |= DOWN;
							Object2.touching |= UP;
						}
					}
					else if(obj1delta < obj2delta)
					{
						overlap = Object1.y - Object2.height - Object2.y;
						if((-overlap > maxOverlap) || !(Object1.allowCollisions & UP) || !(Object2.allowCollisions & DOWN))
							overlap = 0;
						else
						{
							Object1.touching |= UP;
							Object2.touching |= DOWN;
						}
					}
				}
			}
			
			//Then adjust their positions and velocities accordingly (if there was any overlap)
			if(overlap != 0)
			{
				var obj1v:Number = Object1.velocity.y;
				var obj2v:Number = Object2.velocity.y;
				
				if(!obj1immovable && !obj2immovable)
				{
					overlap *= 0.5;
					Object1.y = Object1.y - overlap;
					Object2.y += overlap;

					var obj1velocity:Number = Math.sqrt((obj2v * obj2v * Object2.mass)/Object1.mass) * ((obj2v > 0)?1:-1);
					var obj2velocity:Number = Math.sqrt((obj1v * obj1v * Object1.mass)/Object2.mass) * ((obj1v > 0)?1:-1);
					var average:Number = (obj1velocity + obj2velocity)*0.5;
					obj1velocity -= average;
					obj2velocity -= average;
					Object1.velocity.y = average + obj1velocity * Object1.elasticity;
					Object2.velocity.y = average + obj2velocity * Object2.elasticity;
				}
				else if(!obj1immovable)
				{
					Object1.y = Object1.y - overlap;
					Object1.velocity.y = obj2v - obj1v*Object1.elasticity;
					//This is special case code that handles cases like horizontal moving platforms you can ride
					if(Object2.active && Object2.moves && (obj1delta > obj2delta))
						Object1.x += Object2.x - Object2.last.x;
				}
				else if(!obj2immovable)
				{
					Object2.y += overlap;
					Object2.velocity.y = obj1v - obj2v*Object2.elasticity;
					//This is special case code that handles cases like horizontal moving platforms you can ride
					if(Object1.active && Object1.moves && (obj1delta < obj2delta))
						Object2.x += Object1.x - Object1.last.x;
				}
				return true;
			}
			else
				return false;
		}
	}
}