Fix ccd enabled by default on Bullet bodies

[pouleyKetchoupp]

Fix based on #42643 (comment)

It was due to main_shape_changed being called two times for each added body. The first time it disables ccd, which sets the internal ccd threshold to be 10000. The second time, it enables ccd again because the internal threshold is > 0.

Bodies are now consistently created with disabled ccd by default.

This was causing crashing asserts in Bullet when adding bodies in some scenarios, in btVector3::normalize():
btAssert(!fuzzyZero());

[madmiraal]

I think the problem is that when CCD is disabled, Bullet's ccdMotionThreshold should be set to 0. not 10000.0:

godot/modules/bullet/rigid_body_bullet.cpp

Line 747 in c545146

btBody->setCcdMotionThreshold(10000.0);

First, it defaults to 0.:

godot/thirdparty/bullet/BulletCollision/CollisionDispatch/btCollisionObject.cpp

Line 49 in c545146

m_ccdMotionThreshold(btScalar(0.)),

Second, if it's 0, CCD is not used:

godot/thirdparty/bullet/BulletDynamics/Dynamics/btDiscreteDynamicsWorld.cpp

Line 863 in c545146

if (getDispatchInfo().m_useContinuous && body->getCcdSquareMotionThreshold() && body->getCcdSquareMotionThreshold() < squareMotion)

[madmiraal]

This was causing crashing asserts in Bullet when adding bodies in some scenarios, in btVector3::normalize():
btAssert(!fuzzyZero());

Crashing asserts will still happen with CCD enabled. A separate issue should be raised, because there is a problem with the way that Godot is configuring Bullet CCD.

[pouleyKetchoupp]

This was causing crashing asserts in Bullet when adding bodies in some scenarios, in btVector3::normalize():
btAssert(!fuzzyZero());

Crashing asserts will still happen with CCD enabled. A separate issue should be raised, because there is a problem with the way that Godot is configuring Bullet CCD.

Good point, I'll open a ticket for the CCD issue.

Edit: Opened #43868

[pouleyKetchoupp]

Concerning the way CCD is currently set (threshold of 10000 when disabled) I've decided to keep it this way for now, because this PR is about fixing the crashes that happen without CCD, with minimal changes to current settings.

Edit:
Nevermind this, I had seen some parts of Bullet code that use the threshold without checking if it's 0, but after checking again it looks like it's only in special configurations for CCD, so I might as well simplify things and set it to 0 as you're proposing.

[pouleyKetchoupp]

@AndreaCatania Do you remember why you set the CCD threshold to 10000 instead of 0 when CCD is disabled in PR #28595?

For now, I'm going to set it to 0 to make things more consistent, but let us know if it was solving a specific issue. Looking at Bullet code it shouldn't make a difference in behavior.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.5.