PhysicsServer error with rigid BodySetSpace() GodotPhysics

[starwolfy]

Godot version:

3.2.3 mono official stable.

OS/device including version:

Windows 10 64 bit

Issue description:

When setting the space of a rigid body from a PhysicsServer a stream of a repetitive error occurs with GodotPhysics enabled:
ERROR: The axis Vector3 must be normalized. At: core/math/basis.cpp:980

Steps to reproduce in:

1. Create a space
2. Set space to active
3. Create a body
4. Set body space to space we created earlier.
5. Enable GodotPhysics
6. Watch "The axis Vector3 must be normalized" spam.

Minimal reproduction project:

godotBug.zip

[starwolfy]

This also happens with GDScript

var defaultSpaceState : RID

func _ready():
	
	defaultSpaceState = PhysicsServer.space_create()
	PhysicsServer.space_set_active(defaultSpaceState, true)
	
	var bodyRID : RID = PhysicsServer.body_create(PhysicsServer.BODY_MODE_RIGID,false)
	
	PhysicsServer.body_set_space(bodyRID, defaultSpaceState)
	

[pouleyKetchoupp]

This also occurs with any Rigidbody node with all CollisionShape nodes disabled, or no CollisionShape at all.
It's not a common use case (the body doesn't collide with anything and just falls), but it can be supported by the physics simulation and can be useful for special cases (particles with advanced physics or joint attachments).

Note for junior job:
This is due to how inertia is calculated for a body with no valid shape in Body3DSW::update_inertias():

godot/servers/physics_3d/body_3d_sw.cpp

Lines 79 to 103 in 9b853d7

	// Recompute the inertia tensor
	Basis inertia_tensor;
	inertia_tensor.set_zero();
	for (int i = 0; i < get_shape_count(); i++) {
	if (is_shape_disabled(i)) {
	continue;
	}
	const Shape3DSW *shape = get_shape(i);
	real_t area = get_shape_area(i);
	real_t mass = area * this->mass / total_area;
	Basis shape_inertia_tensor = shape->get_moment_of_inertia(mass).to_diagonal_matrix();
	Transform shape_transform = get_shape_transform(i);
	Basis shape_basis = shape_transform.basis.orthonormalized();
	// NOTE: we don't take the scale of collision shapes into account when computing the inertia tensor!
	shape_inertia_tensor = shape_basis * shape_inertia_tensor * shape_basis.transposed();
	Vector3 shape_origin = shape_transform.origin - center_of_mass_local;
	inertia_tensor += shape_inertia_tensor + (Basis() * shape_origin.dot(shape_origin) - shape_origin.outer(shape_origin)) * mass;
	}

inertia_tensor is initialized to zero and inertias are added from valid shapes (this is correct), but in case there's no valid shape at all it should be set to a valid default inertia with inertia_tensor.set_diagonal(Vector3(1.0, 1.0, 1.0)); to avoid divisions by zero during the simulation.

[Bhu1-V]

hlo Current master branch has some changes in the PhysicsServer so the above code need some changes to run

var defaultSpaceState : RID

func _ready():
	
	defaultSpaceState = PhysicsServer3D.space_create()
	PhysicsServer3D.space_set_active(defaultSpaceState, true)
	
	var bodyRID : RID = PhysicsServer3D.body_create()
	
	PhysicsServer3D.body_set_space(bodyRID, defaultSpaceState)

as u can see body_create() got different syntax and also this code is no longer going to update_inertia(). atleast thats what I'm thinking . and I really don't known what went wrong.

[pouleyKetchoupp]

@Bhu1-V Your sample code works for me on master, I'm able to reproduce the issue. It calls update_inertias() on the next physics step with this callstack:

 	godot.windows.tools.64.exe!Body3DSW::update_inertias() Line 107	C++
 	godot.windows.tools.64.exe!Space3DSW::setup() Line 1165	C++
 	godot.windows.tools.64.exe!Step3DSW::step(Space3DSW * p_space, float p_delta, int p_iterations) Line 147	C++
 	godot.windows.tools.64.exe!PhysicsServer3DSW::step(float p_step) Line 1354	C++
 	godot.windows.tools.64.exe!PhysicsServer3DWrapMT::step(float p_step) Line 76	C++
 	godot.windows.tools.64.exe!Main::iteration() Line 2472	C++
 	godot.windows.tools.64.exe!OS_Windows::run() Line 622	C++

The only difference is body_create creates a body with BODY_MODE_RIGID by default, and body_set_mode needs to be called separately for making it static or kinematic.