From Xojo Documentation
Immediately repaints only the region of the RectControl specified by the X, Y, Width, and Height parameters. If the optional parameter EraseBackground is True, the background will be erased prior to redrawing the area. The default is True.
Calling this frequently can cause the code executing to slow down. It is often preferable to call RectControl.Invalidate instead.
The following refreshes the specified region of the control.