Game Development Reference
In-Depth Information
n.z = 1;
Vr = vel1;
Vrn = Vr * n;
if(fabs(Vrn) <= VELOCITYTOLERANCE) // at rest
{
// Check the relative acceleration:
Ar = Bodies[body1].vAcceleration +
(Bodies[body1].vAngularVelocityGlobal ^
(Bodies[body1].vAngularVelocityGlobal^pt1)) +
(Bodies[body1].vAngularAccelerationGlobal ^ pt1);
Arn = Ar * n;
if(Arn <= 0.0f)
{
// We have a contact so fill the data structure
assert(NumCollisions < (NUMBODIES*8));
if(NumCollisions < (NUMBODIES*8))
{
CollisionData->body1 = body1;
CollisionData->body2 = −1;
CollisionData->vCollisionNormal = n;
CollisionData->vCollisionPoint = tmp;
CollisionData->vRelativeVelocity = Vr;
CollisionData->vRelativeAcceleration = Ar;
CollisionData->vCollisionTangent = (n^Vr)^n;
CollisionData->vCollisionTangent.Reverse();
CollisionData->vCollisionTangent.Normalize();
CollisionData++;
NumCollisions++;
status = CONTACT;
}
}
}
}
return status;
}
That's all there is to this billiards example. As you can see, we used substantially the
same methods shown in other examples throughout this topic to implement this ex‐
ample. About the only new information we've shown here is how to compute rolling
resistance. With a little effort, you can combine the material presented in this example
with the projectile motion material presented in Chapter 6 to model all sorts of sports
balls. Whether you're modeling a billiard ball bouncing off a table or a basketball
bouncing off a backboard, the methods are the same. The only things that will change
are the empirical coefficients you use to model each ball and surface. Have fun.
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