Rotate a KinematicBody according to floor slope

Calebunga

I am trying to make a 3D game in Godot with physics similar to a sonic game in that there should be smooth movement up and down ramps, slopes, etc., and I'm finding that having the player be able to handle slopes is getting to be quite the challenge. I want the character (I'm using a KinematicBody) to rotate according to the slope of the current floor, now matter what angle it may be. I also want the gravity to be in the direction of the floor the player is standing on to make loops possible.

I'm using a Raycast to get the floor normal and have found a way to nearly do it with transform.basis = basis (with basis using the Raycast's normal, as well as up and right vectors: both calculated using normal). The biggest problem right now is that it is setting the character's rotation on all axis, including it's local y-axis, witch is what I need to use for movement rotation.

I've checked many places online and have used a number of different methods, but I think I'm stuck. Guess it could come down to my lack of experience but that's all the more reason for me to ask for help.

TwistedTwigleg

I’ve tried this myself on a platformer prototype and I unfortunately never found a solution that worked, not well at any rate. The hard part I found was keeping the player from “jumping” off rounded surfaces because the player’s forward movement was not curved.

I remember seeing on Twitter, somewhat recently, where someone posted a working sphereical gravity, but I cannot find it now. I did find this tweet from 2017, but there is no code linked, though it might not hurt to ask the user if you are curious.

There is this post on the Godot QnA, which is similar to how I handled it in my prototype. There is also this post on Reddit that might help. Both posts provide example code, which may be helpful in finding a solution.

Also: welcome to the forums!

Calebunga

Thanks! Glad to be here!

That QnA post was exactly what I used to get the variables I needed for my Raycast. I currently have 2 methods that I find can actually rotate the player correctly, but both have some problems:

1: transform.basis = new_basis; new_basis is a variable that I made by rearranging the right, up, and normal vectors that are returned using the script on the QnA post (new_basis = Basis(up, normal, right)). Like I said in my original post, the biggest problem with this is that it is setting the character's rotation on all axis, including it's local y-axis, witch is what I need to use for movement rotation.

2: transform.basis.y = normal; this is actually enough to be able to get most of the rotations I need and none of the ones I don't... BUT... now whenever the Kinematic Body rotates it gets scaled as well, resulting in it getting "flattened".

Not to mention I still don't know what to do with the movement rotation.

Also, out of curiosity, if you are able and willing, could you send me the source code for that prototype of yours? I have a feeling that it could help.

TwistedTwigleg

@Calebunga said: That QnA post was exactly what I used to get the variables I needed for my Raycast. I currently have 2 methods that I find can actually rotate the player correctly, but both have some problems:

1: transform.basis = new_basis; new_basis is a variable that I made by rearranging the right, up, and normal vectors that are returned using the script on the QnA post (new_basis = Basis(up, normal, right)). Like I said in my original post, the biggest problem with this is that it is setting the character's rotation on all axis, including it's local y-axis, witch is what I need to use for movement rotation.

Yeah, I'm not sure on the solution on this. It might be possible to store the rotation offset on the local Y axis, and then after constructing the new basis, reapply that local rotation. That said, from my experiments and projects using rotation (local and global), it is definitely easier said than done.

2: transform.basis.y = normal; this is actually enough to be able to get most of the rotations I need and none of the ones I don't... BUT... now whenever the Kinematic Body rotates it gets scaled as well, resulting in it getting "flattened".

I have not tested it, but if I remember correctly, you can work around this issue doing something like this:

var stored_scale = self.scale
# One way:
global_transform.basis.y = new_basis_vector.normalized() * stored_scale.y
# Another way:
global_transform.basis = new_basis_vector.normalized()
self.scale = stored_scale

Also, out of curiosity, if you are able and willing, could you send me the source code for that prototype of yours? I have a feeling that it could help.

Sure! I sent you a PM with a link to the project.