Supporting top-down mode for 2D

[idanarye]

While most of Tnua's benefits lie in its handling of the vertical axis, one may desire to use it for top-down 2D games. In this mode the floating capsule model is meaningless, of course, and one cannot crouch or jump - but regular movement and dashing should still be useful, and so should be, maybe, other actions that may be added in the future..

[idanarye]

I've tried to implement it in the feature/89/top-down branch by detecting zero gravity when in 2D and setting it to the Z axis (which does not exist in 2D). This works for movement - but it does cause an issue with rotation.

Tnua assumes that Y+ is the up direction and Z- is the fowrard direction. For top-down, we want to switch this.

Instead of a flag for switching, I think it would be best to let the user pass a quaternion which freely defines the directions. Maybe this can be an optional component (TnuaModelOrientation?)

[esmevane]

@idanarye - Hi! I arrived here because I was seeing whether tnua fit top-down control styles.

From a dev ergonomics perspective, an optional Component that controls config like this sounds really nice. It seems like you'd get a bunch of complex stuff (like swapping modes for different levels or w/e) for free because you'd have to design for insertion/removal.