Efficient way to check collision with potentially hundreds of objects

Question

I am trying to make a top down shooter that could potentially have hundreds of objects at once at one point. I need to check collision with projectiles, walls, and enemies. I am currently using ArrayLists which probably won't suffice later on and was wondering if someone had a good method or knows a good method for checking all of those objects at once. This is going to be a game for smartphones and is built in java. Any ideas would be great or if you could point me in some direction that would be fantastic.

Thanks in advance!

Is there a java port of Box2D? otherwise, time to go read up on spatial partitioning schemes. — Matt D, Mar 10 '14 at 03:35
Im using the built in Circle and Rectangle classes that come with libgdx. — G3tinmybelly, Mar 10 '14 at 03:43
And yes there is a java port of box2d but I don't think there is a way to implement that in my game. — G3tinmybelly, Mar 10 '14 at 03:47
Did you read about uniform grids? They are easy to implement. — AturSams, Mar 10 '14 at 07:55
Many other space partitioning options exist. This answer lists some others. http://gamedev.stackexchange.com/questions/21607/documentation-on-2d-space-partitioning/21608#21608 — Seth Battin, Mar 11 '14 at 03:30

score 1 · Answer 1 · answered Mar 10 '14 at 10:00

When I've got huge worlds where enemies can move freely, I tend to create and 2D-array representing e. g. 8x8 tile chunks (I've you're not using tiles, than just take the base unit) and whenever enything is moving, I put a pointer to that object into the specific part of the array the moving thing has been moved into. When doing collusion, I simply do the collusion for object A, I just check intersection with all the other objects in the specific cell of the array and eventually the adjected ones, too.

That's called a uniform grid as mentioned in the comments. – AturSams Mar 10 '14 at 10:03 — AturSams, Mar 10 '14 at 10:03

score 0 · Answer 2 · answered Mar 10 '14 at 10:57

Using chunks like user2241553 suggested is a valid approach. But when you have some algorithm skill, you might want to store any immovable objects in a 2d-tree. A 2d-tree is a binary tree where nodes with even depth are sorted by x-coordinate and nodes with odd depth by y-coordinate. Searching for objects in such a tree which are inside a specific area takes only logarithmic time.

2d trees don't perform that well for objects which move, because whenever an object changes its position it needs to be removed and re-inserted.

Yes, it's logarithmic but unless there are very populations of objects (which is unlikely in a game) then a uniform grid is O(1) — AturSams, Mar 10 '14 at 11:34

Efficient way to check collision with potentially hundreds of objects

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