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# 2D platformer. Find nearest two objects for collision.

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2 replies to this topic

### #1treiguts  Members

Posted 17 October 2012 - 11:22 AM

HI!
I'm working at my very first game, 2D platformer, and I came across collision problem.

Given some random object in map ( object A ), how to find object B for collision check? I attached an image. At bottom, there is blue platform. That specific platform should be checked for collision with 3 objects: player, right and left rock. All other objects doesn't matter. Question: how do I keep link between those objects?

And player, should I brute-check with all objects in map, whether they collide? That seems ineffective.
I wouldn't want to keep two-dimensional array for tile positions, because I have moving objects besides player.

http://i.imgur.com/JnBbz.png

Edited by treiguts, 17 October 2012 - 11:24 AM.

### #2BeerNutts  Members

Posted 17 October 2012 - 12:35 PM

My initial thought is the rocks (or the moving platforms, I assume) should have a set path they follow, so it doesn't worry about colliding with anything. In theory, you should only be checking the controlled objects for collision: The player, the enemies, and the bullets.

So, the player should be checking if he hits any "physical" object (ie, the ground, platforms, wall, etc.), an enemy bullet, a power upgrade, or an enemy.

The enemy should only be checking if he hits the players bullet, or a physical object. He doesn't have to check if he hits the player since the player will handle that check.

The bullet should only be checking for hitting a physical object (wall), since this will destroy it.

So, I would suggest doing this method "brute force" to begin with (have the player check EVERY object) as you probably won't see an issue with your first game.

Later, if you want, you can start to add some smarts by adding a spatial hash (look it up) to your game, and only check other objects within each grid space.

While I think it's a good idea to get a grasp on how objects move and collide within a 2d world, you should really look at 2d physics libraries. They make movement and collision in your 2d world a breeze. My personal favorite is chipmunk-physics, but others like box2d as well.

Good luck, and have fun!

Edited by BeerNutts, 17 October 2012 - 12:38 PM.

My Gamedev Journal: 2D Game Making, the Easy Way

---(Old Blog, still has good info): 2dGameMaking
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"No one ever posts on that message board; it's too crowded." - Yoga Berra (sorta)

### #3treiguts  Members

Posted 17 October 2012 - 12:54 PM

Having read about spatial hashing - that is exactly what I need.

"My initial thought is the rocks (or the moving platforms, I assume) should have a set path they follow, so it doesn't worry about colliding with anything."
I guess it depends - is moving object between static objects? In image, I have 2 moving platforms side by side.

Thanks

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