Collision_detection
Last week I was playing around with a little EaselJS experiment which required me to do collision detection against all items on the screen. This worked fine with a small number of items, but of course, the more items I added, the slower everything became.
I knew that I needed to optimize the code, and pare down the number of collision checks. I have done this before with a grid (even held a contest for it) and was going to port that AS3 code to JavaScript.
If you have read my blog any this week, you have probably noticed that I have been doing some basic research on collision detection within the Flash Player. As part of this, I have put together a simple test suite, showing the performance of a couple of different techniques for checking for collision. This is by no means meant to be exhaustive (and currently tilts towards boundary collision). However, I wanted to post the results as the current information is useful (if nothing more than to confirm existing assumptions), and perhaps generate more tests an ideas around collision detection.
Yesterday I blogged about how you can use the BitmapData.hitTest API to do collision detection between the visible parts of multiple DisplayObject instances. This works very well, but as some of the BitmapData apis can be cpu intensive (particularly new BitmapData and BitmapData.draw) you have to take care to make sure that performance does not get out of hand.
This post will discuss a number of approaches for optimizing collision detection when using BitmapData.
The Flash Player contains a number of APIs for handling collision detection within Flash content. The DisplayObject class contains hitTest and hitTestPoint which can be useful if you need to detect bounding box collisions, or detect collisions between an individual point and bounding boxes or shapes.
However, BitmapData also contains a hitTest API, which can check collisions on BitmapData. Where the API really shines, is when you need to detect collisions between the visible areas of DisplayObjects (and not just of their bounding boxes).
