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From: singer@spar.SPAR.SLB.COM (David Singer)
Newsgroups: comp.windows.news
Subject: Re: fast bitmaps
Message-ID: <1606@spar.SPAR.SLB.COM>
Date: Wed, 21-Oct-87 12:08:13 EDT
Article-I.D.: spar.1606
Posted: Wed Oct 21 12:08:13 1987
Date-Received: Sat, 24-Oct-87 06:35:32 EDT
References: <172@PT.CS.CMU.EDU>
Reply-To: singer@spar.UUCP (David Singer)
Organization: Schlumberger Palo Alto Research - CASLAB
Lines: 12
Summary: Use BuildImage

I've achieved better bitmap drawing/re-drawing by using buildimage and
then imagecanvas/imagemaskcanvas as appropriate, using the canvas as
a cache for the application bitmap.  Of course this is only useful if
you expect to display the same bitmap many times.  Also you may have
to cope with a bitmap editor (I do) and other events that should
invalidate your cache.  Finally you have to decide when to use
imagemask (typically when your source is 1-bit deep, and you want to
draw in the window's default colours), and when to use image (when your
source has true colours in it all by itself).  You should be aware that
1.0 has at least one and possibly several polarity bugs in imagemask and
imagemaskcanvas (i.e. pushing paint through the 1 bits instead of 0), and
for me this varied if the destination was mapped or not ...