Zoom In at mouse location and Zoom out at center of Canvas (Not using ScaleTransform)

Hi

I am writing a small drawing app in WPF. I am using DrawingVisual class to render shapes on Canvas.

I want to implement zoom In/Out for the Canvas control.

1) When I zoom in, zoom focus should be the mouse location.

2) When I zoom out, zoom focus should be the center of Canvas.

Below is the current code that I am trying but results are not satisfactory.                           

When I zoom out all shapes are moving towards the scaled/zoomed center location and not to the Canvas's actual center location.

So please guide me how should I compute the offset X and Y so that shapes will move towards center of canvas.

double zoomFactor = 1.1;
double offsetX = 0;
double offsetY = 0;
protected override void OnMouseWheel(MouseWheelEventArgs e)
{                
        double absoluteMouseX;
        double absoluteMouseY;               
        double centerX = this.ActualWidth / 2; //Canvas center X
        double centerY = this.ActualHeight / 2; // Canvas center Y

        Point relativeMouseToCanvas = e.GetPosition(this);                          

        if (e.Delta > 0)
        {
                absoluteMouseX = relativeMouseToCanvas.X * this.Zoom + offsetX;
                absoluteMouseY = relativeMouseToCanvas.Y * this.Zoom + offsetY;
                this.Zoom *= zoomFactor;
                offsetX = absoluteMouseX - relativeMouseToCanvas.X * this.Zoom;
                offsetY = absoluteMouseY - relativeMouseToCanvas.Y * this.Zoom;
        }

        if (e.Delta < 0)
        {
                absoluteMouseX = centerX * this.Zoom + offsetX;
                absoluteMouseY = centerY * this.Zoom + offsetY;
                this.Zoom /= zoomFactor;

                offsetX = absoluteMouseX - centerX * this.Zoom;
                offsetY = absoluteMouseY - centerY * this.Zoom;
         }

          // Refresh/Repaint shapes on canvas          
}