private void RotateTrackball(Point p1, Point p2, Vector3 rotateAround)
{
// http://viewport3d.com/trackball.htm
// http://www.codeplex.com/3DTools/Thread/View.aspx?ThreadId=22310
Vector3 v1, v2;
if (ConstrainAxis.HasValue)
{
// preparing to compute the ratio to the screen
var diag = Math.Sqrt(
viewport.ActualWidth * viewport.ActualWidth +
viewport.ActualHeight * viewport.ActualHeight
);
// can we project the constraintAxis onto the view?
var t3 = Vector3.TransformCoordinate(ConstrainAxis.Value, camera.CameraInternal.GetViewMatrix());
var dir = new Vector2(t3.X, t3.Y); // axis of Constraint in view coordinates
var pp1 = p1.ToVector2(); // computing distance perpendicular to axis in view coordinates
var r1 = pp1 - (pp1 * dir);
var pp2 = p2.ToVector2(); // computing distance perpendicular to axis in view coordinates
var r2 = pp2 - (pp2 * dir);
var angle = (r2.Length() - r1.Length()) / diag * 4;
// Create the transform
currentRotation *= Matrix.RotationAxis(Vector3.Normalize(ConstrainAxis.Value), (float)(angle * this.RotationSensitivity * 5));
UpdateTransform();
}
else
{
v1 = ProjectToTrackball(p1, viewport.ActualWidth, viewport.ActualHeight);
v2 = ProjectToTrackball(p2, viewport.ActualWidth, viewport.ActualHeight);
// transform the trackball coordinates to view space
var viewZ = camera.CameraInternal.LookDirection;
var viewX = Vector3.Cross(camera.CameraInternal.UpDirection, viewZ);
var viewY = Vector3.Cross(viewX, viewZ);
viewX.Normalize();
viewY.Normalize();
viewZ.Normalize();
var u1 = (viewZ * v1.Z) + (viewX * v1.X) + (viewY * v1.Y);
var u2 = (viewZ * v2.Z) + (viewX * v2.X) + (viewY * v2.Y);
// Could also use the Camera ViewMatrix
// var vm = Viewport3DHelper.GetViewMatrix(this.ActualCamera);
// vm.Invert();
// var ct = new MatrixTransform3D(vm);
// var u1 = ct.Transform(v1);
// var u2 = ct.Transform(v2);
// Find the rotation axis and angle
var axis = Vector3.Cross(u1, u2);
if (axis.LengthSquared() < 1e-8)
{
return;
}
var angle = u1.AngleBetween(u2);
// Create the transform
currentRotation *= Matrix.RotationAxis(Vector3.Normalize(axis), (float)(angle * this.RotationSensitivity * 5));
UpdateTransform();
}
}
