Best way to implement collision detection

Troubleshooting physics
1

Hello,



i implemented collision detection between a box and a node of spheres in my game, but the app become very slow (10-15 FPS) when profiling i saw that there was a lot of memory allocation of Vector3f, here is the code that i use :



[java]Geometry g; // My Box

CollisionResults results = new CollisionResults();

BoundingVolume bv = g.getWorldBound();

node.collideWith(bv, results);

if (results.size() > 0) // Collision

else // No Collision[/java]



What is the best way to optimize the collision detection ?



Thank you for your help

2
  1. You can use jBullet for it. Is faster
  2. Show more code. Show your update function. Memory allocation rising means you create a lot of Vector3f’s just to throw them away.
3
@Dodikles said:
1. You can use jBullet for it. Is faster
2. Show more code. Show your update function. Memory allocation rising means you create a lot of Vector3f's just to throw them away.


I'll try jBullet.
Thank's for your answer, here is more code :

[java]
@Override
public void simpleUpdate(float tpf) {

movePlayer();
moveObstacle(tpf);

camNode.lookAt(geom1.getLocalTranslation(), Vector3f.UNIT_Y);
camNode.setLocalTranslation(camtranslation.setX(geom1.getLocalTranslation().x));
}


private void moveObstacle(float tpf) {
sphereGroup.getNode().rotate(0, 1f*tpf, 0);
sphereGroup2.getNode().rotate(0, -1f*tpf, 0);


CollisionResults results1 = new CollisionResults();
BoundingVolume bv = geom1.getWorldBound();
sphereGroup.getNode().collideWith(bv, results1);

if (results1.size() > 0) {
player.setPhysicsLocation(new Vector3f(0, 5f, 0));
player.setLinearVelocity(new Vector3f(0,0,0));
}

sphereGroup2.getNode().collideWith(bv, results1);
if (results1.size() > 0) {
player.setPhysicsLocation(new Vector3f(0, 5f, 0));
player.setLinearVelocity(new Vector3f(0,0,0));
}

}

private void movePlayer() {
speed = player.getLinearVelocity();
player.setAngularVelocity(Vector3f.ZERO);
if (geom1.getLocalTranslation().y >=-8.95f) {
// speed = new Vector3f(0,0,0); //geom1.getLocalTranslation();
if (left) { if(speed.x > -4f) speed.x -= 0.4f; }
if (right) { if(speed.x < 4f) speed.x += 0.4f; }
if (up) { if(speed.z > -4f) speed.z -= 0.4f; }
if (down) { if(speed.z < 4f) speed.z += 0.4f; }
if( left || right || up || down){
//player.setWalkDirection(new Vector3f(v.x,v.y,v.z));
//geom1.setLocalTranslation(v);

player.setLinearVelocity(speed);
}
}

}
[/java]
4

Here are the profiling for the CPU :



http://imageshack.us/photo/my-images/812/cpuq.png/



And for the memory :



http://imageshack.us/photo/my-images/40/memoryil.png/

5

Well, I cannot say if this is the culprit since I don’t know the amount of calls, but it could be: You create new Vector3f’s everytime you encounter collisions. If this happens a lot ( I mean a lot) then you create a bunch of useless objects on every update. Just define those two vectors outside somewhere and reference them instead of "new"ing…

1 Like
6

Collision creates a lot of vectors but thats not exactly whats resource intense about it. You collide a bounding volume with geometry, if you need to do that often you should probably reside to kinematic rigidbodies and physics raytests and sweeptests.

1 Like
7

Thank’s normen and Dodikles, Kinematic is working like a charm :slight_smile: