necessary due to the more accurate mouse move events that are useful for sculpting and painting (at least on Linux/X11, not sure about other platforms). If the update function takes a while to run, this in turn causes more mouse move events to be accumulated, making things even slower, .. going into a spiral of slower and slower redraws. As a solution I've added a INBETWEEN_MOUSEMOVE event next to MOUSEMOVE. A MOUSEMOVE event is automatically changed to INBETWEEN_MOUSEMOVE when a MOUSEMOVE event is added after it. This new event type is only handled by painting/sculpting operators, everything else can happily ignore it.