Thanks for the great book!
I've completed the first one but I couldn't really grasp this part 100%.
I was wondering if you could point to any resources where I could see, in particularly, where 'r = w x I.w' comes from?

Probably it's derived from the other equations in the book but I couldn't figure it out.

Hi,

Love the book and it's really helped me get some physics into my in development game engine.

I wanted to share that I think there is an issue in the angular velocity and friction example. My sphere never rotated whenever it impacted the ground and first I thought it was some mistake in my code with the calculation of angular velocity and the impulses but then I noticed you have the ground have its m_friction set to 0.0f. This makes total friction 0.

In my readings elsewhere, I believe that any contact where there is no friction for a sphere with its center of mass equal to that of its position would result in no rotations at all. Correct me if I am wrong here please as I am very new to game physics.

I had to set the ground friction to something other than 0.0f (I set it 1.0f) in order to achieve a result which looks realistic (at least to my eyes).

P.S - I could not find any contact information and anywhere else to share feedback or issues found in the book so posted it here. If this is not the right place, let me know.

When I use the following code, everything works normally:

// Dynamic Bodies
for (int x = 0; x < 6; x++) {
for (int y = 0; y < 6; y++) {
float radius = 0.5f;
float xx = float(x - 1) * radius * 2;
float yy = float(y - 1) * radius * 2;
body.m_position = Vec3(xx, yy, 10.0f);
body.m_orientation = Quat(0, 0, 0, 1);
body.m_linearVelocity.Zero();
body.m_invMass = 1.0f;
body.m_elasticity = 0.5f;
body.m_friction = 0.5f;
body.m_shape = new ShapeSphere(radius);
m_bodies.push_back(body);
}
}

But if I change the limits from 6 to 15, it will happen:

If I move the mouse, strange things happen ... What could be wrong?

Thank you for the excellent book!

In page 56, I think the code for solving quadratic equation in function RaySphere is wrong.

const float delta = b * b - a * c;

However, I think the correct one should be:

const float delta = b * b - 4 * a *c;