Dealing with the FlxU.overlap kill in Flixel 2

FlxU.overlap in Flixel 2 uses the new FlxQuadTree to handle collisions. It allows you to pass in either a single object (say an FlxSprite), a group of objects (FlxGroup), or even a group of groups! To be honest the more you give it, the more useful it proves to be.

However it’s got one annoying side-effect: if you don’t specify a custom function to deal with the collision, it will kill() your objects. This is often a far from ideal end result. For example if you had a bullet and an enemy being compared – you may want the bullet to be killed instantly, but the enemy to be only “hurt” by this, reducing it’s health.

The only way I’ve found to do this so far is to override the “kill” method of FlxSprite (in my Enemy class) and then perform the logic in there. Reduce health, update animation, health < 0, then kill it for real.

This isn’t ideal, but it certainly works – so if you’re stuck in a similar bind with FlxU.overlap, this may help.

Also it’s worth mentioning (as this caught me out too) – if you do specify a custom function for overlap, make sure it returns a Boolean. False will ignore the overlap, true will say you’ve dealt with it. If you don’t return this value it appears to default to killing your objects again.

Posted on March 22nd 2010 at 10:47 pm by .
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  • October 21st 2010 at 11:39 pm

    Ah yes, overlap has been giving me a headache for hours! Still haven’t managed to get my bullets to destroy when they collide with a Tilemap… :S

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