Try using the WaitCursor:
// activate the wait cursor
SetWaitCursor (1);
// do your calculation and display results
// deactivate the wait cursor
SetWaitCursor (0);
Note that with the wait cursor active, mouse clicks are stored for processing after wait cursor is set inactive. If you want to disable all clicks, use InstallPopup() to display your graph panel with a disabled (dimmed) OK button. When your calculation is done, enable (undim) the OK button and RemovePopup(0) when user clicks on OK.