Path: utzoo!attcan!uunet!husc6!purdue!decwrl!nsc!jon
From: jon@nsc.nsc.com (Jon Ryshpan)
Newsgroups: comp.windows.x
Subject: Re: inverting areas
Message-ID: <5081@nsc.nsc.com>
Date: 23 May 88 05:00:05 GMT
References: <324@piring.cwi.nl> <15077@sgi.SGI.COM>
Reply-To: jon@nsc.UUCP (Jon Ryshpan)
Organization: National Semiconductor
Lines: 21

In article <15077@sgi.SGI.COM> mtoy@xman.SGI.COM
			       (Michael Toy -- The S.G.I. XMAN) writes:
>XOR is not my idea of a good way to highlight (or "invert" an area).
>Consider a not-at-all-hypothetical machine which has a lot of horsepower
>dedicated to graphics operations.  Almost any graphics operations happens
>"instantly", text, lines, rects, fills, you can draw these things 10,000's
>of times a second.  In order to get this performance, this machine is designed
>so that the frame buffer memory is not on the CPU memory bus, making the
>READ/XOR/WRITE time quite slow (in comparison to the time to draw things).
>On this architecture, it is much faster to invert an object by drawing
>again with the "foreground" and "background" colors switched than it is
>to do an XOR.

This will be the situation with systems using many of the graphics
display chips which have been introduced in the last few years.  Both
the NSC and the TI chips lend themselves to systems like this.  Their
performance will drive out systems which use the same processor for
computation and graphics.  Their prices are appropriate for systems as
low as the upper end of the AT range.  So we are not talking about high
end systems like Silicon Graphics.  Therefor beware the very dangerous
XOR.