Error with Quad Tree when making shotgun.

[FlixelCommunityBot]

Issue #196 by: test84

Hi,

If you want to create something like a shotgun where multiple small bullets move together, if any of them collides, the adjacent ones will get collided. In order to fix it I temporarily increased world divisions to 64: FlxG.worldDivisions = 64; but that doesn't help when you stand next to a tile and shoot, it will have bullets go through them.

Let me know if you need an example and I'll mail you my game.

-test84

[Dovyski]

Right now increasing FlxG.worldDivisions directly impacts Flixel performance because a new QuadTree is created for every call to overlap(). There is a fix for that creation problem.

Since there was no response by the author in the original issue, I think it's safe to close this issue.

[greysondn]

It'd be nice if the original user had responded. I'm not wholly aware but can confirm a similar issue that can be reproduced.

Basically, if you create a square flxSprite and place a decent sized group of them with no space together (we did 10x10 for a total of 100), set them to collide with one another, then collide with a given one - wow! Behavior is occasionally erratic, but for the better part - especially with any amount of physics applied - it can take several seconds to several minutes for the code's execution to come back to a normal pace.

This is partly a bad design choice on the developer's part (setting up for expensive collisions)... But there may be something worth examining here.

I agree that to some extent closing this issue if we don't have a user to query is a good idea, as @Dovyski has suggested. I'm not wholly aware whether the user has indicated the same issue I'm able to confirm and only offer it as a supplementing point.

[Dovyski]

What @greysondn described is related to the original issue to some extent, as I see things. @moly already suggested we give some thoughts about how other engines process the collision, so we can borrow some ideas and improve Flixel.

Fixing the QuedTree creation for every frame greatly improves performance, but it's not a silver bullet to solve all collision problems. We definitely need to investigate that further for the next "featue release".

[Dovyski]

Since the original author did not respond to this issue and @greysondn created a pull request with @moly fixes improving the quadtree creation per update, I'm closing this issue.

If we face that same problem in the future, let's approach it using the improved quadtree code.