Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!horus.sgi.com!thant From: thant@horus.sgi.com Newsgroups: comp.sys.sgi Subject: Re: # of overlay planes Message-ID: <8908162116.AA29747@horus.sgi.com> Date: 16 Aug 89 21:16:22 GMT References: <8908161833.AA12079@castor.wustl.edu> Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 20 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@sgi.com