How is the rotate tool implemented?

Unity Engine
1

I’d like to replicate the rotation tool in the editor in-game and can’t seem to derive how the 2D mouse motions are mapped to positive & negative rotations. Depending on the orientation of the object there seems to be a direction where you can drag the mouse and have no rotation and, perpendicular to that, a direction that maximizes the rotation (see attached gifs).

8511293--1134170--NoRotation.gif 8511293--1134176--MaxRotation.gif

Could some one help me understand how the mapping of 2D mouse motion to positive/negative rotation happens?

EDIT: I believe the directions are the tangent line at the point clicked and the radial projected into screen space?

2

Looks like it takes the angle from origin to mouse in that plane of rotation, then observes changes in that angle and applies them.

I did that in the enclosed package with 2D rotation… see the second (righthand) one.

Relevant codelet:

    void PerformCircularRotation()
    {
        // where is our center on screen?
        Vector3 center = Camera.main.WorldToScreenPoint(transform.position);

        // angle to previous finger
        float anglePrevious = Mathf.Atan2(center.x - lastPosition.x, lastPosition.y - center.y);

        Vector3 currPosition = Input.mousePosition;

        // angle to current finger
        float angleNow = Mathf.Atan2(center.x - currPosition.x, currPosition.y - center.y);

        lastPosition = currPosition;

        // how different are those angles?
        float angleDelta = angleNow - anglePrevious;

        // rotate by that much
        transform.Rotate(new Vector3(0, 0, angleDelta * Mathf.Rad2Deg));
    }

6201992–680924–RotateZViaDrag.unitypackage (20 KB)