PhysicsDirectSpaceState.intersect_ray returns a different result with Bullet and GodotPhysics

[QazPolma]

Godot version:
3.3.2.stable

OS/device including version:
Linux Mint 20.1(Ubuntu 20.04 LTS)

Issue description:
When raycasting from the center of a KinematicBody to another KinematicBody with "get_world().direct_space_state.intersect_ray", I get different results depending on PhysicsEngine.
With "Bullet" I get the second body and with "GodotPhysics" I get the first body.

Steps to reproduce:
1.Make 2 KinematicBody objects.
2.Raycast between the 2 bodies.
3.Change "Project settings->Physics->3D->Physics Engine"

Minimal reproduction project:

RaycastBug_v2.zip

Edit: Removed the exclusion lists issue, since it was because of incorrect setup.

[pouleyKetchoupp]

I can confirm the inconsistency between Bullet and Godot Physics.

Exclusion lists should work though. In your project, you're setting self in the exclusion list for the raycast, and because the script is on the root node, it doesn't affect the raycast. You would need to set the kinematic body itself in the exclude list to make it work properly.

[QazPolma]

Thank you for the explanation. I have updated the case accordingly.

[rburing]

The behavior of raycasts with Bullet in this case is due to the following code:

godot/thirdparty/bullet/BulletCollision/NarrowPhaseCollision/btSubSimplexConvexCast.cpp

Lines 135 to 137 in c08e753

	//don't report time of impact for motion away from the contact normal (or causes minor penetration)
	if (result.m_normal.dot(r) >= -result.m_allowedPenetration)
	return false;

Even if that weren't there, there would still be this check:

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

Lines 638 to 639 in c08e753

	//add hit
	if (castResult.m_normal.length2() > btScalar(0.0001))

There are no settings in Bullet to change this behavior, so besides documenting this there is not much we can do (unless someone changes Bullet upstream).

In GodotPhysics in master there is a hit_from_inside parameter that can be passed in to intersect_ray.

[prominentdetail]

This may be related, but I found that having a collisionShape that has its Z extents set below 0.5 will cause GodotPhysics to fail to hit it (in this case the intersect_ray is traveling along the X axis straight through the object). It works fine in Bullet physics, but not in GodotPhysics.