Pool collision detection

quote:

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Original post by OmniBrain
As I remember that article they consider one sphere being stationary, so the effective speed of object 2 just is v2-v1.
in your case if sphere 1 is moveing left with 1 m/s and the other is moving left with 2 m/s, the effective speed would be 1m/s toward left.

now you also have to put in where your spheres are located, but the right sphere moving with 2m/s (effective 1m/s) will move toward the one on left side...

hope this will answer your question

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quote:

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Original post by SpaceDude
I haven''t read the article... but it sounds like what they are saying is, if you have balls A and B with velocity Va and Vb at positions Pa and Pb.

if (DotProduct(Pb-Pa, Va-Vb) < 0)
{
// No collision
}

This means if the balls are moving away from each other (relatively), then don''t collide. Otherwise you may get your balls stuck into each other, if for example the balls come in to collision and you reflect the velocities. Then on the next frame if the balls haven''t had time to move apart yet, you may detect another colision and reflect the velocities again. And so your balls will just stick together and vibrate, reflecting velocity each frame.

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		// First, find the normalized vector n from the center of 

		// circle1 to the center of circle2

		Vector *player1pos = player1->turnPositionIntoVector();
		Vector *cometpos = comet->turnPositionIntoVector();

		Vector *n = vectorBetweenTwoPoints(player1pos, cometpos);
		//source of possible errors if this is in the wrong order


		normalize(n);


		// Find the length of the component of each of the movement

		// vectors along n. 

		// a1 = v1 . n

		// a2 = v2 . n


		//get v1 and v2

		Vector *v1 = new Vector();
		v1->x = player1->getDirection()->x;
		v1->y = player1->getDirection()->y;

		Vector *v2 = new Vector();
		v2->x = comet->getDirection()->x;
		v2->y = comet->getDirection()->y;

		GLdouble a1 = dot(v1, n);
		GLdouble a2 = dot(v2, n);

		// Using the optimized version, 

		// optimizedP =  2(a1 - a2)

		//              -----------

		//                m1 + m2

		GLdouble optimizedP = (2.0 * (a1 - a2)) / (player1->getMass() + comet->getMass());

		// Calculate v1'', the new movement vector of circle1

		// v1'' = v1 - optimizedP * m2 * n

		Vector *v1prime = new Vector(); 
		v1prime->x = v1->x - optimizedP * comet->getMass() * n->x;
		v1prime->y = v1->y - optimizedP * comet->getMass() * n->y;

		// Calculate v1'', the new movement vector of circle1

		// v2'' = v2 + optimizedP * m1 * n

		Vector *v2prime = new Vector();
		v2prime->x = v2->x + optimizedP * player1->getMass() * n->x;
		v2prime->y = v2->y + optimizedP * player1->getMass() * n->y;

                //this is where i set the player''s resultant

//direction.  This keeps on pushing me across the comet

//if i hit the comet from "behind"


		xPushBack = v1prime->x * player1->getSpeed();
		yPushBack = v1prime->y * player1->getSpeed();

		//this is where i set the comet''s resultant

//direction

		comet->setDirection(*v2prime);

quote:

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Original post by grekster
Not all collisions result in a change of direction for both balls. Say ball A and ball B are both moving in the same direction and ball A collides with B, ball A could continue in the same direction but just be travelling slower.

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Vector Vel = pObj2->Vel() - pObj1->Vel();
float m1 = pObj1->InverseMass();
float m2 = pObj2->InverseMass();
float m  = m1+m2;

const float restitution = 0.3f;

Vector dV = Normal * -((1.0f + restitution) * Vel.Dot(Normal));

pObj1->Vel() -= dV * (m1 / m);
pObj2->Vel() += dV * (m2 / m);