# of overlay planes

[thant at horus.sgi.com]

Howdy,

Yeah, people have been telling me about a lot of machines that have eight 
overlays.

If you are only doing greyscale stuff, you could use colormap mode with
writemask.  The colormap is twelve bits big, so the bottom eight would
contain the picture and the top four could be overlay.  This is separate
from the overlay planes proper so you only get twice the colors, not n 
squared.

Another thing you might think about is keeping a copy of the image in the
z-buffer, and go ahead and draw right on top of the image in the display
planes, and any time you wanted to "erase" or "move" the overlay, just
copy portions or the whole picture back from the z-buffer using rectcopy.

This would allow your overlays to be double-buffered.

thant at sgi.com