view independent graphics on the window

Hello-

We are using openCascade in our application with great results and are finding it very easy to use. However, I have one view related problem that I can't seem to figure out.

We would like to place a trihedron in the lower left corner of the screen, always at the same screen coordinates, as a sort of visual indication of the view direction. That is, the trihedron always appears M pixels from the left edge, and N pixels from the bottom edge of the view window, and always has a fixed size of P pixels, regardless of the view direction, mapping, or limits. (This is similar to the functionality of the UCS icon in AutoCAD.)

Is this possible, and if so, where can I find some sample code or what classes/functions should I look at?

Thanks in advance,
Eric.