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steg

Collision detection on minecraft type landscape - i.e. Voxels

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steg    390

Hi,

 

I've generated a 'world' made up of voxels - think minecraft.  I'm using AABB for collision.  My issue is, what to do when collision occurs, so if moving forwards and collision, stop forward movement, if collision occurred while strafing left, stop left movement.  I kind of did this but if I am moving forwards and collision occurs and then I turn the player around say 90 degrees and then move forward, I still can't as still thinks there is a collision...How can I sort this out, do I need some form of plane intersection or normal vector?

 

Any help is much appreciated.  Link to video of issue below:

 

https://www.youtube.com/watch?v=bbxRRBDBWRQ

 

Thanks,

Steve

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slicer4ever    6769

Push or slide?

I'd take the center point of the voxel, and the center point of the colliding object, get the plane of the face you are closest colliding to, then slide against that plane. I simplify the concept, but from watching the video, and the problem you describe, it sounds like your object is "inside" the voxel, so it's constantly colliding. when you detect collision, you need to resolve it such that you are no longer actually colliding with the voxel.

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steg    390

Thanks for that.

 

So, when there is a collision, you need to resolve so there isn't one?  Is this what the slide would do?

 

Thanks again.

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slicer4ever    6769

Thanks for that.
 
So, when there is a collision, you need to resolve so there isn't one?  Is this what the slide would do?
 
Thanks again.

Basically. You add the velocity to your object, figure out the plane of the voxel your closest to, then you figure out the closest point to that plane that does not cause an intersection with the plane. this has the added benefit of producing a sliding effect if done correctly.

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If you're moving each axis individually you may as well just do a check for each of them (easier to code, though I'm not sure how much it affects performance). You'd still have slide behavior since each axis is affected separately. Depends on how you're handling this, though.

 

If you happen to know how to handle collision against tiles in 2D you can apply the same logic here. Voxels are pretty much 3D tiles.

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steg    390
public class CollisionLibrary {
	public static boolean testAABBAABB(final AABB box1, final AABB box2) {
		   if (Math.abs(box1.center.x - box2.center.x) > (box1.r[0] + box2.r[0])) return false;
		   if (Math.abs(box1.center.y - box2.center.y) > (box1.r[1] + box2.r[1])) return false;
		   if (Math.abs(box1.center.z - box2.center.z) > (box1.r[2] + box2.r[2])) return false;
		   return true;
		}
	
	public static float sqDistPointAABB(final Vector p, final AABB aabb) {
		   float sqDist = 0.0f;
		   float v;
		   float minX, minY, minZ, maxX, maxY, maxZ;
		      
		   // get the minX, maxX, minY, maxY and minZ, maxZ points of the AABB
		   minX = aabb.center.x - aabb.r[0];
		   maxX = aabb.center.x + aabb.r[0];
		      
		   minY = aabb.center.y - aabb.r[1];
		   maxY = aabb.center.y + aabb.r[1];
		      
		   minZ = aabb.center.z - aabb.r[2];
		   maxZ = aabb.center.z + aabb.r[2];
		      
		   // test the bounds against the points X axis
		   v = p.x;
		      
		   if (v < minX) sqDist += (minX - v) * (minX - v);
		   if (v > maxX) sqDist += (v - maxX) * (v - maxX);
		      
		   // test the bounds against the points Y axis
		   v = p.y;
		      
		   if (v < minY) sqDist += (minY - v) * (minY - v);
		   if (v > maxY) sqDist += (v - maxY) * (v - maxY);
		      
		   // test the bounds against the points Z axis
		   v = p.z;
		      
		   if (v < minZ) sqDist += (minZ - v) * (minZ - v);
		   if (v > maxZ) sqDist += (v - maxZ) * (v - maxZ);
		      
		   return sqDist;
		}
	
		public static boolean testCircleAABB(final Circle circle, final AABB box) {
		   // get the squared distance between circle center and the AABB
		   float sqDist = sqDistPointAABB(circle.center, box);
		   float r = circle.radius;
		      
		   return sqDist <= r * r;
		}
	
}
 

 

Thanks,
 
I'm using a bog standard sphere to AABB collision detection as shown in the code.  The issue I'm having is what to do when a collision occurs, for instance, if I move forwards and there is a collision, I then cannot move forwards which is correct, but if I turn around say 90 degrees and then move forward, I should be able to move, but cannot.  I think you need to check the surface normals or something...

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That sounds like you're checking for the collision before moving (which means that as soon as you collide with something you can't move anymore as you're always colliding). I'm not sure, but just guessing out of the behavior.

 

I'm really suspicious about how you do the sphere/box check though... It's like you're trying to turn the box into a sphere o_O Is that correct?

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steg    390

Hi,

 

The sphere/AABB is working fine, no issue with that.  I'm checking for collision before moving, could that be part of the problem? The code

is shown:

 


CollisionType coll = this.isCollision(0);

if (Keyboard.isKeyDown(Keyboard.KEY_W))// move forwards
			{
				direction = 0;

				if (coll != CollisionType.FRONT) {
					camera.walkBackwards(.1f);
				}

			}

 

I am really surprised how difficult this is proving to me!

 

This is the isCollision method:

 

private CollisionType isCollision(int dir) {

		Vector3f v = this.camera.getCameraPosition();

		float tempx = (v.x) / BLOCKWIDTH * BLOCKHEIGHT;
		int tempX = (int) tempx;

		float tempz = (v.z) / BLOCKWIDTH * BLOCKHEIGHT;
		int tempZ = (int) tempz;

		float tempy = (v.y) / BLOCKWIDTH * BLOCKHEIGHT;
		int tempY = (int) tempy;

		int bx = (int) tempX;
		int by = (int) tempY;
		int bz = (int) tempZ;

		bx = bx % BLOCKWIDTH;
		bz = bz % BLOCKHEIGHT;
		by = by % BLOCKHEIGHT;

		int zchunk = Math.abs(tempZ / Chunk.CHUNK_SIZE) * WORLDWIDTH;
		int xchunk = Math.abs(tempX / Chunk.CHUNK_SIZE);
		int chunktoget = zchunk + xchunk;

		CollisionType collisionType = CollisionType.NONE;

		Block b = null;
		b = ChunkManager.getInstance().getBlockInChunk(chunktoget,
				Math.abs(bx), (int) Math.abs(by), Math.abs(bz));

		// Check ground
		if (b != null && b.IsActive()) {
			// playerSphere radius is 1
			Vector playerPosition = new Vector();
			playerPosition.x = Math.abs(v.x);
			playerPosition.y = Math.abs(v.y);
			playerPosition.z = Math.abs(v.z);
			playerSphere.update(playerPosition, 1.0f);

			AABB voxel = new AABB(1f, 1f, 1f); // width, height, depth
			Vector voxelPosition = new Vector();
			voxelPosition.x = Math.abs(bx);
			voxelPosition.y = Math.abs(by);
			voxelPosition.z = Math.abs(bz);
			voxel.update(voxelPosition);

			if (CollisionLibrary.testCircleAABB(playerSphere, voxel)) {
				collisionType = CollisionType.GROUND;
				System.out.println("GROUND COLLISION");
				groundLevel = (int) voxelPosition.y;
			}
		}

		// Check chunk for any collisions - should have early bail out
		for (int x = 0; x < Chunk.CHUNK_SIZE; x++) {
			for (int y = this.ground; y < Chunk.CHUNK_SIZE; y++) {
				for (int z = 0; z < Chunk.CHUNK_SIZE; z++) {
					b = ChunkManager.getInstance().getBlockInChunk(chunktoget,
							x, y, z);

					if (b != null && b.IsActive()) {

						Vector playerPosition = new Vector();
						playerPosition.x = Math.abs(v.x);
						playerPosition.y = Math.abs(v.y);
						playerPosition.z = Math.abs(v.z);
						playerSphere.update(playerPosition, .8f);

						AABB voxel = new AABB(1f, 1f, 1f); // width, height,
															// depth
						Vector voxelPosition = new Vector();
						voxelPosition.x = x;
						voxelPosition.y = y;
						voxelPosition.z = z;
						voxel.update(voxelPosition);

						if (CollisionLibrary
								.testCircleAABB(playerSphere, voxel)) {
							System.out.println("COLLISION on Direction:"
									+ direction);
							if (direction == 0) {
								collisionType = CollisionType.FRONT;
							}
							if (direction == 1) {
								collisionType = CollisionType.BACK;
							}
							if (direction == 2) {
								collisionType = CollisionType.LEFT;
							}
							if (direction == 3) {
								collisionType = CollisionType.RIGHT;
							}
							return collisionType;
						}
					}
				}
			}
		}

		return collisionType;
	}

 

 

Thanks for your input and advice, I really appreciate it.

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steg    390

Maybe I need to do a dot product on the surface I've collided with?

Edited by steg

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