Rotate graphic towards mouse in WPF (like an analog dial)

Question

In WPF/C# how would I rotate a \"graphic\" to face the current mouse position?

Basically what I want is a \"wheel\" UI Control (like an analog volume dial

Answer 1

In my case i have dynamically created shapes which shall rotated toward mouse direction. To solve this I used a lightweight function. All I need is following:

• The centerpoint of the current selected shape
• The point from the last mouseover step
• And the point from the current mouseover step

It is not necessary to use methods from the Math library. I calculate the angle which depends on the difference of the current mouse over point and the previous mouse over point and the position in relation o the center point. Finally I add the angle on the exisitng angle of the current object.

private void HandleLeftMouseDown(MouseButtonEventArgs eventargs)
{
    //Calculate the center point of selected object
    //...
    //assuming Point1 is the top left point
    var xCenter = (_selectedObject.Point2.X - _selectedObject.Point1.X) / 2 + _selectedObject.Point1.X
    var yCenter = (_selectedObject.Point2.Y - _selectedObject.Point1.Y) / 2 + _selectedObject.Point1.Y
    _selectedObjectCenterPoint = new Point((double) xCenter, (double) yCenter);

    //init set of last mouse over step with the mouse click point
     var clickPoint = eventargs.GetPosition(source);
    _lastMouseOverPoint = new Point(clickPoint.X,clickPoint.Y);
}

private void HandleMouseMove(MouseEventArgs eventArgs)
{
    Point pointMouseOver = eventArgs.GetPosition(_source);                            

    //Get the difference to the last mouse over point
    var xd = pointMouseOver.X - _lastMouseOverPoint.X;
    var yd = pointMouseOver.Y - _lastMouseOverPoint.Y;

    // the direction depends on the current mouse over position in relation to the center point of the shape
    if (pointMouseOver.X < _selectedObjectCenterPoint.X)
        yd *= -1;
    if (pointMouseOver.Y > _selectedObjectCenterPoint.Y)
        xd *= -1;

    //add to the existing Angle   
    //not necessary to calculate the degree measure
    _selectedObject.Angle += (xd + yd);

    //save mouse over point            
    _lastMouseOverPoint = new Point(pointMouseOver.X, pointMouseOver.Y);
}