Sleeps make the script lose focus.

Why don't you just use the built-in dragging functions the Graal has for GUIs? You can set canmove=false and the drag functions will still be triggered when dragging, just the GUI wouldn't move.

I think you can figure out what to do with that data, right?

I've always had problems with this... for instance, it looses focus and stops triggering when the mouse is moved outside of the GUI. I don't think anyone moves their mouse slow enough to allow the client to keep up. At least, this was one of my problems. I also had problems with focus and such... it was just a pain that I gave up. Perhaps there are fixes for this, however.