Relative 3D rotation

[placid relic]

Rotation is relative to the parent by default. You must use "global_rotation" to make it non-relative.

[frank jasper]

The problem with that is I don't set the parent of the picked up object to the camera, so I can't just use the relativity of the parent as a solution

[solemn gust]

Do you mean you want to rotate the object as though its up and right axes perfectly point up and right on the screen?

[frank jasper]

Yep, that's it

[solemn gust]

IIRC there are ways to rotate a vector by passing in an arbitrary up and right vectors, so presumably passing in the camera's up and right vectors would achieve that. I think it involves quaternions... I'll see it I can quickly find it

[frank jasper]

Oh no, quaternions

[solemn gust]

I just woke up so I could well be wrong about this 😂 But I think if you use the vector representing the camera's rotation and the vector representing the object's rotation as as parameters for Quaternion(arc_from, arc_to), you could then multiply your camera-relative rotation by that resulting quaternion to get the equivalent rotation in object-space

Oh, or if that doesn't work, you could maybe figure out the axis of the rotation you want in camera-space, transform that into object-space using Quaternion(arc_from, arc_to), and then use Quaternion(axis, angle) to get the rotation

This is where I'd start tinkering if I were trying to do this myself anyway

[frank jasper]

Alright, give me a moment to try that out

[frank jasper]

I am now realizing that I have no idea how to try and use this

[solemn gust]

You can multiply Vector3 by Quaternion. I think in Godot the vector needs to be on the right (according to the doc), so for example Rotation = Quaternion * Rotation should rotate the vector by the quaternion

I haven't worked with Quaternion in Godot though, only in other frameworks, so there may be quirks about implementation

[frank jasper]

👍

[frank jasper]

Quaternions don't seem to work

Or I'm just too dum to understand them

But I made a drawing, hopefully explain how I want the rotation to work if anyone else wants to try helping:
https://cdn.discordapp.com/attachments/1260592101758996550/1260598440434339850/image.png?ex=668fe748&is=668e95c8&hm=2314d39d5e67abe1d69d766e3d702f97d5d0444d7680f15db097f98706b057ac&

Basically like skewering the object

[solemn gust]

Darn; hopefully someone else has a better idea. Without digging into it myself I don't think I can offer further advice; this is the kind of thing I'd spend a while googling and testing out

[frank jasper]

UPDATE: I figured it out.

var prev_mouse_pos: Vector2
func _process(delta):
   var new_mouse_pos = get_viewport().get_mouse_position()
   var pos = new_mouse_pos - prev_mouse_pos
   var angle = pos * 0.01
   currentGrab.global_rotate(global_transform.basis.x,angle.y)
   currentGrab.global_rotate(global_transform.basis.y,angle.x)
   prev_mouse_pos = new_mouse_pos