Home
Blogs
Forums
News
Portfolios
Projects
Tutorials
46 users logged in
New? Learn about game development.
Before posting, review our community guidelines.
Follow Us
Chat in the GameDev.net Discord!
Mastodon
Back to Graphics and GPU Programming

bounding box collision detection not working right....

Started by
3 comments, last by steg 11 years ago

As you can tell from the title, bounding box collision detection is not working out for me....*sigh* Here's my problem:


bool EntityManager::checkCollision(Entity* ent1, Entity* ent2)
{
	bool cholided = false;
	AABB* box1 = ent1->getBoundingBox();
	AABB* box2 = ent2->getBoundingBox();
	
	if(box1->getMin().getX() > box2->getMax().getX()) return cholided;
	if(box1->getMax().getX() < box2->getMin().getX()) return cholided;
	if(box1->getMin().getY() > box2->getMax().getY()) return cholided;
	if(box1->getMax().getY() < box2->getMin().getY()) return cholided;
	if(box1->getMin().getZ() > box2->getMax().getZ()) return cholided;
	if(box1->getMax().getZ() < box2->getMin().getZ()) return cholided;

	
	return (cholided == true);
}

this code seems to be OK since I got this from a programming math book. link: http://gamemath.com/ now I'm not sure if there's a problem with my code in the bounding box, but i don't think so since it renders fine. Maybe I'm doing something weird? anyways, the book also talked about checking a box against a moving box (a player for instance) and gave this code.


double EntityManager::checkCollisionAgainstMovingEnt(Entity* movingEnt, Entity* staticEnt, Vector3 & d)
{
	// large number to return if no intersection
	const double noIntesection = 1e30f;
	AABB* otherAABB = staticEnt->getBoundingBox();
	AABB* movingBox = movingEnt->getBoundingBox();
	// interval for time consideration
	double dEnter = 0.0;
	double dLeave = 1.0;

	if(d.getX() == 0.0f)
	{
		if((otherAABB->getMin().getX() >= movingBox->getMax().getX()) || 
			(otherAABB->getMax().getX() <= movingBox->getMax().getX()))
		{
			return noIntesection;
		}
		else
		{
			// divide once

			bool divByZero = (d.getX() != 0);

			double oneOverD = 1.0 / d.getX();

			double xEnter = (otherAABB->getMin().getX() - movingBox->getMin().getX()) * oneOverD;
			double xLeave = (otherAABB->getMax().getX() - movingBox->getMax().getX()) * oneOverD;

			if(xEnter > xLeave)
				swap(xEnter,xLeave);

			if(xEnter > dEnter) dEnter = xEnter;
			if(xLeave < dLeave) dLeave = xLeave;

			if(dEnter > dLeave)
				return noIntesection;
		}


	}
	// check y
	if(d.getY() == 0.0f)
	{
		if((otherAABB->getMin().getY() >= movingBox->getMax().getY()) ||
			otherAABB->getMax().getY() <= movingBox->getMin().getY())
		{
			return noIntesection;
		}
		else 
		{
			// divide by one on the y axis.
			double oneOverD = 1.0 / d.getY();

			double yEnter = (otherAABB->getMin().getY() - movingBox->getMax().getY()) * oneOverD;
			double yLeave = (otherAABB->getMax().getY() - movingBox->getMin().getY()) * oneOverD;

			if(yEnter > yLeave)
				swap(yEnter,yLeave);

			if(yEnter > dEnter) dEnter = yEnter;
			if(yLeave < dLeave) dLeave = yLeave;

			if(dEnter > dLeave)
				return noIntesection;
		}
	}

	// check z-axis
	if(d.getZ() == 0.0f)
	{
		if((otherAABB->getMin().getZ() >= movingBox->getMax().getZ()) ||
			otherAABB->getMax().getZ() <= movingBox->getMin().getZ())
		{
			return noIntesection;
		}
		else 
		{
			// divide by one on the y axis.
			double oneOverD = 1.0 / d.getZ();

			double zEnter = (otherAABB->getMin().getZ() - movingBox->getMax().getZ()) * oneOverD;
			double zLeave = (otherAABB->getMax().getZ() - movingBox->getMin().getZ()) * oneOverD;

			if(zEnter > zLeave)
				swap(zEnter,zLeave);

			if(zEnter > dEnter) dEnter = zEnter;
			if(zLeave < dLeave) dLeave = zLeave;

			if(dEnter > dLeave)
				return noIntesection;
		}


	}
	return dEnter;
}

here's a screen shot also: http://puu.sh/2zKM0

I'm not really sure why collision detection doesn't work for me....here's how i'm using it:


	for(int i = 0; i < 10; i++) {
		
		
	//	if(pack->getPosition().getX() > pallets->getPosition().getX())
	//	{
	//		pallets->setColor(0.5,1,0,1);
	//		pallets->draw();

	//		pack->setColor(1,1,0,1);
	//		pack->setDebugColor(1,0.5,1,0.5);
	//		pack->draw();
	//	}
		
	//	if(pack->getPosition().getY() > pallets->getPosition().getY())
	//	{
	//		pallets->draw();
	//		pack->draw();
	//	}
		bool collide = entMgr->checkCollision(pack,wall);
		char buffer3[256];
		sprintf_s(buffer3,256,"Collision: %d",collide);
		Vector3 d;
		d.setVector(2,1,2);
		
		double interval = entMgr->checkCollisionAgainstMovingEnt(pack,wall,d);
		char buffer4[256];
		interval += 0.04;
		sprintf_s(buffer4,256,"interval: %.2f",interval);
		if(interval <= d.getX() && interval <= d.getY() && interval <= d.getZ())
		{
			pack->setColor(interval,1,0,1);
		}
		output(0,300,buffer4);
		output(0,500,buffer3);
		if(collide)
		{
			pack->setColor(1,0,0,0.5);
			AABB* pbox = pack->getBoundingBox();
			AABB* wbox = wall->getBoundingBox();

			bool contains = pbox->containsPoint(0,0,0);
			bool contains2 = wbox->containsPoint(-100,100,0);
			char buffer[256];
			sprintf_s(buffer,256,"collision: %d",collide);
			output(100,100,buffer);
		}
	}

I don't know maybe I need to think this through. this is for a school project keep in mine I'm not asking for you to do it for me and the collision detection is all me, the teacher just wanted a simple pack man.

Advertisement

In the function


bool EntityManager::checkCollision(Entity* ent1, Entity* ent2)

In the case they intersect, you return




return (cholided == true);

bt what you're doing is comparing cholided to true, and return the result of that.

Cholided is always set to false, so that comparison will always return false, since chomparison is not true.

Use




return true;

instead.

Also, you wouldn't need the variable cholided. Just return false in every case except the last.

that still didn't do anything. shouldn't the collision detection work whether an AABB is static or moving? this is getting annoying for me.....

Hi,

Don't know if this will help, this is java AABB I use, should be simple to port to C++.


package com.voxby.game;

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;
		}
	
}

package com.voxby.game;

public class AABB {
	public Vector center;
	public float r[];

	public AABB(final float width, final float height, final float depth) {
		center = new Vector();
		r = new float[3];
		r[0] = width * 0.5f;
		r[1] = height * 0.5f;
		r[2] = depth * 0.5f;
	}

	public void update(final Vector position) {
		center.x = position.x;
		center.y = position.y;
		center.z = position.z;
	}
}

package com.voxby.game;

public class Vector {
	public float x;
	public float y;
	public float z;

	public Vector() {
		x = 0.0f;
		y = 0.0f;
		z = 0.0f;
	}

	// returns the (squared) distance between this Vector and another
	public float distSQ(final Vector vec) {
		float distX = x - vec.x;
		float distY = y - vec.y;
		float distZ = z - vec.z;
		return distX * distX + distY * distY + distZ * distZ;
	}
}

If it isn't working, take a bath, have a think and try again...

Oh and to use:


Vector playerPosition = new Vector();
			playerPosition.x = Math.abs(v.x);  // get player X,Y,Z
			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);  // get object X,Y,Z
			voxelPosition.y = Math.abs(by);
			voxelPosition.z = Math.abs(bz);
			voxel.update(voxelPosition);

			if (CollisionLibrary.testCircleAABB(playerSphere, voxel)) {
// do whatever 
                        }

If it isn't working, take a bath, have a think and try again...

This topic is closed to new replies.

Advertisement

Popular Topics

Aybe One
How do you manage yourself and your time as years pass on? GDNet Lounge
Jikoob
Too many managers? General and Gameplay Programming
aigan
The promise of freedom in story games Game Design and Theory
robertrobert
Facebook Ads for sales on steam, does it work? Games Business and Law
gjl
New Generated Constructor & JIT Issue AngelCode
MrK45
Inheriting from application registered class AngelCode
Advertisement

Recommended Tutorials

Hairein
Indie Device Anxiety Syndrome (IDAS) Career Development
Myopic Rhino
The Art of Modeling Lens Flares Graphics and GPU Programming
Myopic Rhino
Programming 3D Sound With OpenAL in Windows General and Gameplay Programming
Myopic Rhino
Open Source and the Gaming Industry Business and Law
Gaiiden
GameDev.net Posting Guidelines Archive

Reticulating splines

About GameDev.net
Community Guidelines
Terms of Service
Privacy Policy
Contact Us
Copyright (c) 1999-2024 GameDev.net, LLC
Back to Top