bitdemo.icn: Program to demonstrate bitplanes

   bitdemo illustrates some of the techniques made available by the
bitplane package in the program library.

   The upper rectangle is drawn using three bitplanes, reserving
one plane for each of the primary colors.  After clicking one of
the "draw" or "erase" buttons, you can draw or erase any one of
the bitplanes independently of the others.  Notice what happens
when the colors overlap.

   Drawing is not constrained to the rectangle so that you can see
some of the possible consequences of using the bitplane routines
improperly.

   The lower rectangle is drawn using four other bitplanes, one each
for the four types of objects.  Click once on a button to bring the
objects of that type to the front.  Click a second time to make them
invisible.