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Collision Detection with Flash MX

Article Description

Collision detection is all about detecting objects and boundaries on the stage. Matthew David illustrates how to use collision detection in an arcade-style game.

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Hitting the Blocks

The blocks across the screen are controlled programmatically. Each block is an instance of the same block. A color effect is applied to each to change the color of the blocks. In addition, the following script is applied to each block:

onClipEvent (load) {
   startX = this._x
}

This script is used to tell the block to hide if it is crossed by the ball movie clip. The only difference between each block is the instance name; each block has a different name that starts with the word Tile and is followed by a number between 1 and 35.

At the top of the script, you tell the game how many blocks are on the stage:

TileNum = 36;

You then tell Flash how to calculate that the object just hit is a block:

function maketargetList (numOfTiles) {
   for (i=0; i<numOfTiles; i++) {
     TargetList[i] = String("tile"+(i+1));
   }
}

The final step is to add the script that will do something when a block when it is hit:

   //check if ball hits a tile
   var theTileNum = TargetList.length;
   for (i=0; i<theTileNum; i++) {
     var thisTile = TargetList[i];
     if (this.MovieClip.hitTest(_root[thisTile])) {
        this.increaseSpeed();
   Total += (10 * CurrentBallNum);
   _root[thisTile]._x += -1000;
        TargetList.splice(i, 1);
        this.flipY();
   if (TargetList.length == 0) {
          resetGame();
        }break;
     }
   }

Here the script verifies that a target is hit and then increases the games score by 10 points after the collision. The complete game can be seen in Figure 3.

Figure 3Figure 3 The final game.


BreakOut demonstrates collision with a boundary and with a static object.

6. Colliding Onwards | Next Section Previous Section