rws@EXPO.LCS.MIT.EDU (Bob Scheifler) (11/16/88)
If you do graphics in the viewport and then scroll around, you lose the graphics that have been done. You also can't do graphics off of the displayed viewport (almost a necessity). If you want the graphics to be retained, you need to enable backing-store for the widget (and any inferiors, sorry) that you place inside the viewport that you want the graphics retained for. Alternatively, you can try enabling save-unders on just the viewport window, but some implementations of save-unders may discard graphics to save-undered regions. You also need to have a server (like those in R3) that support backing-store or save-unders.