TrackballCamera

<csharp>

using UnityEngine; using System.Collections;

public class TrackballCamera : MonoBehaviour {

public float distance = 15f;

public float virtualTrackballDistance = 0.25f; // distance of the virtual trackball.

public GameObject target; private Vector3? lastMousePosition; // Use this for initialization void Start () { var startPosn= (this.transform.position - target.transform.position).normalized *distance; var position = startPosn + target.transform.position; transform.position = position; transform.LookAt (target.transform.position); }

// Update is called once per frame void LateUpdate () { var mousePosn = Input.mousePosition;

var mouseBtn = Input.GetMouseButton (0); if (mouseBtn) { if (lastMousePosition.HasValue) { // we are moving from here var lastPosn = this.transform.position; var targetPosn = target.transform.position;

// we have traced out this distance on a sphere from lastPosn /* var rotation = TrackBall( lastMousePosition.Value.x, lastMousePosition.Value.y, mousePosn.x, mousePosn.y ); */ var rotation = FigureOutAxisAngleRotation(lastMousePosition.Value, mousePosn);

var vecPos = (targetPosn - lastPosn).normalized * -distance;

this.transform.position = rotation * vecPos + targetPosn; this.transform.LookAt(targetPosn);

lastMousePosition = mousePosn; } else { lastMousePosition = mousePosn; } } else { lastMousePosition = null; }

}

Quaternion FigureOutAxisAngleRotation (Vector3 lastMousePosn, Vector3 mousePosn) { if(lastMousePosn.x == mousePosn.x && lastMousePosn.y == mousePosn.y) return Quaternion.identity;

Vector3 near = new Vector3(0,0,Camera.mainCamera.nearClipPlane);

Vector3 p1 = Camera.mainCamera.ScreenToWorldPoint( lastMousePosn + near ); Vector3 p2 = Camera.mainCamera.ScreenToWorldPoint( mousePosn + near);

//WriteLine("## {0} {1}", p1,p2); var axisOfRotation = Vector3.Cross(p2,p1);

var twist = (p2-p1).magnitude / (2.0f * virtualTrackballDistance);

if(twist > 1.0f) twist = 1.0f; if(twist < -1.0f) twist = -1.0f;

var phi = (2.0f * Mathf.Asin(twist)) * 180/Mathf.PI ;

WriteLine("AA: {0} angle: {1}",axisOfRotation, phi);

return Quaternion.AngleAxis(phi, axisOfRotation); }

Quaternion TrackBall(float p1x, float p1y, float p2x, float p2y, float radius) { // if there has been no drag, then return "no rotation" if(p1x == p2x && p1y == p2y) { return Quaternion.identity; } var p1 = ProjectToSphere( radius, p1x,p1y ); var p2 = ProjectToSphere( radius, p2x,p2y );

var a = Vector3.Cross(p2,p1); // axis of rotation // how much to rotate around above axis var d = p1 - p2; var t = d.magnitude / (2.0f * radius); // clamp values to stop things going out of control. if(t > 1.0f) t = 1.0f; if(t < -1.0f) t = -1.0f; var phi = 2.0f * Mathf.Asin(t); phi = phi * 180/Mathf.PI; // to degrees

return Quaternion.AngleAxis(phi, a); }

/// <summary> /// Projects an x,y pair onto a sphere of radius distance. /// OR onto a hyperbolic sheet if we are away from the center /// of the sphere /// </summary> /// <returns> /// The point on the sphere. /// </returns> /// <param name='distance'> /// Distance. /// </param> /// <param name='x'> /// X. /// </param> /// <param name='y'> /// Y. /// </param> Vector3 ProjectToSphere(float distance, float x, float y) { float z; float d = Mathf.Sqrt(x*x + y*y); if(d < distance * 0.707f) { // inside sphere z= Mathf.Sqrt(distance*distance - d*d); } else { // on hyperbola var t = distance / 1.4142f; z = t*t /d; }

return new Vector3(x,y,z); } }

</csharp>