Path: utzoo!attcan!uunet!mcvax!guido
From: guido@cwi.nl (Guido van Rossum)
Newsgroups: comp.windows.x
Subject: Re: inverting areas
Message-ID: <331@piring.cwi.nl>
Date: 21 May 88 19:15:34 GMT
References: <324@piring.cwi.nl> <15077@sgi.SGI.COM>
Reply-To: guido@cwi.nl (Guido van Rossum)
Organization: The Royal Society for Prevention of Cruelty to Amoebae
Lines: 27

Michael Toy -- The S.G.I. XMAN writes:
>XOR is not my idea of a good way to highlight (or "invert" an area).
>...
>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.

Yes.  But redrawing with changed background is also not a good way to
highlight or "invert" an area.  On some architectures redrawing with
different fg/bg colors is slower than XOR-ing some bit planes, on other
architectures it is slower.  What have we learned?  It depends.  It is
unavoidable that some programs will perform sub-optimal on some
architectures (although most programs perform sub-optimal on all
architectures :-).

Is your SGI architecture also slow at copying pixmaps around on the
screen?  This is another operation where the source is already in the
frame buffer.  I believe it is quite an essential assumption of the X
design (in fact of any window system's design) that such operations are
fast, so moving windows around is fast.

Returning to XOR, maybe this can be recognized as an important graphics
operation and the primitives for XOR-ing bit planes in-place built in
the hardware...
--
Guido van Rossum, Centre for Mathematics and Computer Science (CWI), Amsterdam
guido@piring.cwi.nl or mcvax!piring!guido or guido%piring.cwi.nl@uunet.uu.net