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Site Graphics and Multimedia Design Forum

Collision Detection
for a landscape in Flash...

 1:42 pm on Mar 13, 2002 (gmt 0)

I want to create some complex collision detection for a landscape environment where the good old bounding boxes of Movie Clips and hitTest() probably isn't going to be suitable.

Imagine a Lander type game - what would be the best way to do such collision detection?




 9:00 pm on Mar 14, 2002 (gmt 0)

Think I've cracked it...

By having the 'landscape' as a Movie Clip with transparent background you can use landscape.hitTest(object._x, object._y, true). This takes an explicit x-y coord and returns true if it falls on a part of the landscape that isn't transparent. Ideal for Lander;)



 9:09 pm on Mar 14, 2002 (gmt 0)

Interesting! You'd utterly lost me on your original post, but please sticky me with a URL when you get it working... I'd love to get a look at the effect.


 9:45 am on Mar 15, 2002 (gmt 0)

There probably won't be a URL as I'm just learning Flash and going through the motions - every time I find something I might want to do, I want to learn the best way of doing it - fussy like that;)

If you want to try the effect it's pretty easy to set it up.

- Create a movie clip and draw some abstract shape leaving the background 'empty' (transparent). Place this on the root timeline. Name the instance of this movie clip something eg: 'landscape'.

- If you were making a game you'd probably have some sprite that you wanted to test for collisions with the background, but for brevity we'll just use the mouse. Principle's the same.

- To add some output (so you can see when there is a collision) add a dynamic textbox called 'outputField' to the root timeline.

- In the ActionScript Panel for your landscape movie clip instance insert the following script:

if (this.hitTest(_root._xmouse, _root._ymouse, true))
_root.outputField = 'hit';
_root.outputField = '';

- Test your movie - you should see that when the mouse pointer is over a populated part of your movie clip your dynamic text box shows 'hit' and when it's not it should be blank.

A useful effect for anyone wanting to create 2D games etc

- To use this type of collision detection you have to specify an exact x-y coord in the hitTest function. However this throws up a question... What if my 'sprite' is bigger than a single pixel (which it's likely to be). Easy - in your if (hitTest statement here) test you need to add more hitTests as part of the if statement (OR) where each x-y coord represents a different corner of your 'sprite'. You'd use the getBounds(_root) method to let flash work this out for you - check the ActionScript dictionary for a full explanation of that method.

- also, if there's an error in the above let me know as I'm writing from memory - my copy of Flash is at home!

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