To handle the Delete All button, we need to empty various data structures that are local to our main loop (that is, not accessible from the mouse event callback function), so we change to the Delete All mode and then we can delete everything from inside the main loop. We also must deal with the user clicking the main window (that is, not a button). If they clicked on one of the people on the right-hand side, then we want to select that person and change to Collection mode. Or if they
clicked in the main window while in Collection mode, then we want to change to Training mode. This is done as follows: