In TX Text Control .NET for WPF 16.0, we implemented a new property that returns the mouse position in device independent units relative to the client area.

This property is very useful when you need to get the current mouse position without using events such as MouseUp or MouseDown. The following code can be used to set the current input position to the current mouse position:

Graphics g = Graphics.FromHwnd(IntPtr.Zero);
float resX = 1440 / g.DpiX;

textControl1.InputPosition = new TXTextControl.InputPosition(
    new System.Drawing.Point(
        (int)(textControl1.MousePosition.X * resX + textControl1.ScrollLocation.X),
        (int)(textControl1.MousePosition.Y * resX + textControl1.ScrollLocation.Y)));