Gravity Simulation & Collision detection

1

Hi there folks…

i have a small problem, i have to simulate gravity on a character with collision detection, now every thing works fine, just a little problem occurs when i character has gravity and it hit the top object when key is not pressed , the character passes right through the top hurdle…

here is the image of swf file…

The code which moves the character is here, but first i would like to thank SENOCULAR for his KeyObject Class which makes life easier …

package 
{
	import flash.display.MovieClip;
	import flash.display.Stage;
	import com.senocular.utils.KeyObject;
	import flash.ui.Keyboard;
	import flash.events.Event;
	import flash.geom.Rectangle;

	public class Character extends MovieClip
	{
		private var stageRef:Stage;
		private var key:KeyObject;
		public var speed:Number = 0.5;
		public var vx:Number = 0;
		public var vy:Number = 0;
		public var friction:Number = 0.9;
		public var maxSpeed:Number = 8;
		public var gravity:Number = 0.98;
		public var bounds:Rectangle;
		public var xCollide:Boolean;
		public var yCollide:Boolean;

		public function Character ()
		{
			addEventListener (Event.ADDED_TO_STAGE, addedToStage);

		}
		// when added to stage.....
		private function addedToStage (eve:Event):void
		{
			stageRef =this.stage;
			//get key input on stage..
			key = new KeyObject(stageRef);
			//define the boundries of the character;
			bounds = new Rectangle(0,0,stageRef.stageWidth,stageRef.stageHeight);
			//event listener to move character...
			addEventListener (Event.ENTER_FRAME, moveChar, false, 0, true);
		}
		private function moveChar (eve:Event):void
		{
			//accelerate the character when key is pressed...
			if (key.isDown(Keyboard.LEFT))
			{
				vx -= speed;
			}
			else if (key.isDown(Keyboard.RIGHT))
			{
				vx += speed;
			}
			else
			{
				// reduce the speed when key is up...
				vx *= friction;
			}
			if (key.isDown(Keyboard.UP))
			{
				gravity = 0;
				vy -= speed;
			}
			else if (key.isDown(Keyboard.DOWN))
			{
				gravity = 0;
				vy += speed;
			}
			else
			{
				gravity = 0.98;
				//reduce the speed when key is up...
				vy *= friction;
			}
			//determine the max speed of character so it should not exceed that..

			if (vx > maxSpeed)
			{
				vx = maxSpeed;
			}
			else if (vx < -maxSpeed)
			{
				vx = -maxSpeed;
			}
			if (vy > maxSpeed)
			{
				vy = maxSpeed;
			}
			else if (vy < -maxSpeed)
			{
				vy = -maxSpeed;
			}
			//determin the boundries of our character 
			if (this.x > bounds.width)
			{
				this.x = bounds.width;
			}
			else if (this.x < bounds.x)
			{
				this.x = bounds.x;
			}
			if (this.y > bounds.height)
			{
				this.y = bounds.height;
			}
			else if (this.y < bounds.y)
			{
				this.y = bounds.y;
			}
			//check for collisions to bounce back the character.
			if (xCollide)
			{
				vx = -vx;
				xCollide = false;
			}
			if (yCollide)
			{
				if (gravity != 0)
				{
					vy = -2;
				}
				else
				{
					vy = -vy;
				}
				yCollide = false;
			}
			// update the position of character on stage...
			this.x += vx;
			this.y += vy;

			//rotate the object on stage
			this.rotation = vx*2 ;
			
			this.y += gravity;

		}
	}
}

and here is the document class for main movie

package
{
	import flash.display.*;
	import flash.events.*;
	import com.dataflat.HitTestObj;
	
	
	public class CollisionTest extends Sprite
	{
		public function CollisionTest():void
		{
			init();
		}
		
		private function init():void
		{
			addEventListener(Event.ENTER_FRAME, doEnterFrame);
		}
		
		private function doEnterFrame(eve:Event):void
		{
			var hitTest = HitTestObj.checkCollisions(circle_mc, hurdle_mc);
			
			if (hitTest)
			{
				circle_mc.xCollide = true;
				circle_mc.yCollide = true;
				trace ("got collision.....");
			}
		}
	}
}

if some one can please help me out with this, i will be dearly thankful…:smiley: