One of the challenges with GPU drawings is the selectors used to resize an object. In this case I have drawn 3 rectangles and have the selectors as part of the rectangle drawing using a different ZIndex. Sadly the ZIndex only work on the locat drawing, so as the middle is selected it’s selectors are hidden behind the object in front of it. The 2nd challenge is that selectors are zoomed as the diagram is zoomed, meaning they can get very small.
One possibility is to have a 3rd diagram for selectors. The grid is on a separate diagram that is in background. I can do the same for diagram UI which in that case would include more advanced UI controls for rotation, in-line edit etc. That will work since the ZIndex on the new diagram is in front of the two others – just keep the background Transparent.