body_test_motion not available in gdscript on PhysicsServer

[rminderhoud]

Godot version:
master

Issue description:
body_test_motion() is available on Physics2DServer but not in the 3D server (PhysicsServer). It would be quite useful to have in 3D physics to implement custom physical motions.

[MrModez]

Can we please fix that? I don't think it's too much work :c

[notverymoe]

Just ran into this myself. I don't imagine this should be too difficult, would it be fine for me to take a crack at it?

[RevenantX]

you can use this https://docs.godotengine.org/en/3.2/classes/class_physicsdirectspacestate.html instead (and for some things this is better choice)

[notverymoe]

That's a significant amount of code required to work around an asymmetrically exposed method, imo, it'd be easier to just manually expose it unless you've got a need for some more unique work cases (which godotengine/godot-proposals#710 helps with in a lot of cases)

[Calinou]

The way the source code is organized seems to make this nontrivial. PhysicsServer3D doesn't have body_test_motion, but PhysicsServer3DSW does. yet, we want to expose it in PhysicsServer3D to be consistent with 2D. Any ideas?

[notverymoe]

body_test_motion exists on PhysicsServer3D as a pure virtual method (line 494 in the header) implemented by both backends.

So, exposing it only requires the same setup as the 2D version, namely a wrapper around MotionResult, and a proxy method. Did have a crack at it before and got it working, but ran into some issues (segfault) with passing it certain Rigidbodies - which were, from memory, any non-kinematic bodies.

[pouleyKetchoupp]

Closed by #50102 (4.0) & #50103 (3.4)