[Bullet] KinematicBody slides on collision box, but doesn't on a plane

[Zylann]

Godot 3.1 beta10

After being confused about what #17893 became, I decided to recreate an issue about the initial point:
If you move a KinematicBody with move_and_slide(), and make it move towards a box, it will slide on it.
However, if you move towards a plane, it will get stuck in it and doesn't slide. This is unexpected, it should slide just like with the box.

I want to emphazise that in my project I use Rigidbodies and they slide just fine on planes, which I use for the floor of the world. I don't see any reason why Planes would be some sort of exception when using KinematicBodies, besides being inconsistent. The fact they are infinite surely prevents making holes or doors, but that's the normal behavior of planes, you may actually want that.

This project demonstrates the problem:
KinematicBodyOnPlane.zip

I see several other issues where the bottom line always ends up as "it's not meant to be walkable", or "it's infinite". Those are not explanatory enough to me.
The Plane shape exists and is different from a huge quad because it doesn't need to specify a size and doesn't seem to suffer from tunnelling. Also, it's there, and working in every other case.

So I see two options:

• Either this particular move_and_slide case with KinematicBodies must be fixed for good
• Or we explicitely make it not collidable, show a warning, and state in the doc that shape is only meant for Areas (even though I still don't understand what technical limitation would push us to do that). But if that other choice is taken, that's removing a feature and then breaking compatibility.

[abhinavsagar]

I dont think that is a bug as plane shape is infinite in Godot. To see its effect use some navmesh like covering structured over it .

[Zylann]

I dont think that is a bug as plane shape is infinite in Godot

How is that related to the fact a rigidbody slides on it but a kinematic doesn't?

[pouleyKetchoupp]

Can be still reproduced in 3.2.4 beta 5, but occurs only when using Bullet Physics (default settings). Switching to Godot Physics 3D fixes the issue.

[akien-mga]

This seems still reproducible in 3.5 RC 1.