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usb2killer

Jumping instead Sliding

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I'm programming a physics engine for a racing game. I'm using sphere terrain intersection. I trying to test it by using spheres over a terrain. The result is that the spheres are jumping instead of sliding along the terrain. What to do? checking collision...
for (int i=1;i<physicsComponents.size();i++) {

iCollisionObject sphere=physicsComponents.get(i).GetNextCollisionObject(fps/30);
//iCollisionObject sphere=physicsComponents.get(i).getCollisionObject();

Float3D normal = cground.IsTouchingN(sphere);

if (normal != null) {
physicsComponents.get(i).Collision(normal);
}
}

Collision(normal):
public void Collision(Float3D normal) {
movementForce.AddToThis(normal.Multiply(-1f * movementForce.Length()));
}

Updating the physicsComponents:
if (mass!=0) {
setPosition(position.Add(movementForce.Multiply(1f / fps)));
movementForce.AddToThis(acc.Multiply(1f / fps));

rotation = rotation.Add(rotationForce);

acc = gravity.Clone();
}

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Don't really get what your doing at the moment, detecting a collision then just pushing them apart?

This explains how to do collisions with sliding:
http://www.peroxide.dk/download/tutorials/tut10/pxdtut10.html

it uses ellipsoid space but if your only using spheres then it will be much easier. If you don't want to use sweep tests for all your collisions then you could do:

Store current position
move object
check collisions
if no collisions, done
else move object back to previous position
preform sweep test + sliding

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its been over a year since I read it so I'm not entirly sure myself now. If you check his original paper http://www.peroxide.dk/papers/collision/collision.pdf he has the code int he appendix at the end.

As for using spheres, instead of putting seperate values for the Ellipsoids (x, y, z) just do (radius, radius, radius). Once you get it working for a single triangle its simple to loop through all your faces (cull as needed) to find the closest collision.

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