Collision Detection in Actionscript 3

In Actionscript 3.0 there are two methods to detect collisions which are: the hitTestObject and the hitTestPoint. Firstly, the hitTestObject detects whether two display objects have collided or overlapped. I have previously made a tutorial on the hitTestObject which can be found here. The hitTestPoint detects whether a display object has intersected with a specified x & y point.

This tutorial will show you how to detect collisions using the hitTestPoint method which will detect whether the mouse’s x and y position has collide with an object. I have used a simple circle for the object in this tutorial, but any object can be created.


Collision Detection in Actionscript 3

Step 1

Open a new Flash AS3 file.
Select the oval tool and draw a simple circle shape on the stage like below. I have used #0000FF colour, but you can use whatever colour you wish.




Step 2

Select your circle shape and convert it into movie clip (F8). Then give it the instance name: ‘ball_mc’ as shown below.




Step 3

Select the text tool with dynamic text and drag a textbox below your circle like below:



Now give the dynamic text box the instance name: “hitText_txt”.


Step 4

On the timeline create a new layer called “Actions”. Select the first frame and hit F9 to open up the actions panel and enter the following code:

//1.
stage.addEventListener(Event.ENTER_FRAME, detectCollision);

//2.
function detectCollision(event:Event) {
if (ball_mc.hitTestPoint(mouseX,mouseY,true)) {
hitText_txt.text="Ball hit";
} else {
hitText_txt.text="No hit";
}
}

Code:
1. This adds an event listener to the stage with the enter frame event and the detectCollision parameter.
2. This function checks whether the mouse’s x & y position has collide with the ball object. The third parameter for the hitTestPoint method is the shapeflag which checks for the actual pixel of an object (true) or the bounding box (false).


Step 5

Test your collision detection Ctrl + Enter. Now move your mouse over the ball and you should see a different message.



You should now be able to perform collision detection in Actionscript 3.0.