# Collision detection help?

**URL:** <https://forum.kirupa.com/t/collision-detection-help/246993>\
**Category:** flash\
**Created:** [December 17, 2007, 4:41pm UTC](https://forum.kirupa.com/t/collision-detection-help/246993 "2007-12-17T16:41:38Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Awesome\_O\_4000](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Awesome\_O\_4000](https://forum.kirupa.com/u/Awesome_O_4000)\
**Post date:** [December 17, 2007, 4:41pm UTC](https://forum.kirupa.com/t/collision-detection-help/246993/1 "2007-12-17T16:41:38Z")

</div>

Hi everyone. I was wondering if anyone could help me with a little collision detection. Basically, I have a grid set up. The grid’s tiles have a gravity variable, so they all fall. However, I don’t want them to. I want them to check to see if there are tiles beneath them, so they stop falling when they hit.

Some sample code:

```php

var tileClasses:Array = [Blue, Green, Black, Yellow, Red];
var grid:Array = new Array( 9 );
var i:int = -1;
var spacing:Number = 3;
var gravity:Number = .025;
var vy:Number = 0;
while ( ++i < 9 ) {
    var column:Array = new Array( 9 );
    grid[i] = column;
    var j:int = -1;
    while ( ++j < 9 ) {
        var randomClass:Class = tileClasses[Math.floor( Math.random() * tileClasses.length )];
        var tile:DisplayObject = addChild( new randomClass() );
        MovieClip( tile ).markedForRemoval = false;

        //all of your positioning/event listening as was
        tile.x = (i*((tile.width)+spacing)+50);
        tile.y = (j*((tile.height)+spacing)+50);
        this.addChild(tile);
        tile.alpha = .35;
        tile.addEventListener(MouseEvent.MOUSE_OVER, overHandler);
        tile.addEventListener(MouseEvent.MOUSE_OUT, outHandler);
        tile.addEventListener(MouseEvent.CLICK, clickHandler);
        tile.addEventListener(Event.ENTER_FRAME, enterHandler);

        column[j] = tile;
    }
}

```

Here is my enterHandler method:

```php

function enterHandler(event:Event):void {
    var tile:Object = event.target;
    vy += gravity;
    event.target.y += vy;
        
        if (event.target.y + event.target.height / 2 > stage.stageHeight) {
            event.target.y = stage.stageHeight - event.target.height / 2;

            trace("hit the ground");
        }
    }
}

```

Right now I have them falling and they hit the bottom of the stage perfectly. I was more just using that to test my gravity. What I really want is, like I said, to have the tiles stop falling when they hit the tiles below. I’ve tried using a hitTestObject, and I’m sure that’s what I need to do, but I couldn’t get it to work properly.

Can anyone lend a hand?