Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!oliveb!amiga!jimm
From: jimm@amiga.UUCP (Jim Mackraz)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga mentality
Message-ID: <5544@amiga.UUCP>
Date: 11 Apr 90 22:00:26 GMT
References: <16296@snow-white.udel.EDU> <11059@bsu-cs.bsu.edu> <6647@wehi.dn.mu.oz> <3452@newton.physics.purdue.edu>
Reply-To: jimm@superman.UUCP (Jim Mackraz)
Organization: Commodore-Amiga Inc, Los Gatos CA
Lines: 34

In article (Sho Kuwamoto) writes:
)Heh?  I agree, the blitter is probably the reason.  However, the mac
)does *not* refresh the entire screen when a window is uncovered.  It
)updates only the portions of the window which were uncovered, even
)if that portion is oddly shaped (semi-circular, say).

Likewise, the Amiga window refresh, when required, is done through
the "damage region."

)When windows are obscured on the Amiga, does the OS keep around a
)bitmap of the covered area, or is the program responsible for
)remembering what was there?  The mac uses the latter technique which
)saves on memory, but loses on speed.

Amiga lets the programmer pick the refresh method that best suits
the application:  application refresh, offscreen bitmaps for just
the obscured portions ("Pike-style layers"), or contiguous offscreen
full-window buffering (which also supports bitmap scrolling and
optimizes the rendering to onscreen/offscreen pixels).

Apart from the blitter, I don't know exactly why Amiga windows look faster,
if they do.  Saved offscreen bitmaps certainly help, and the Amiga
layers are optimized for front-back operations.  The processor runs a
little faster in typical modes than Macs used to when going to the
memory-mapped display buffer.  Of course, that has changed in recent
Macs ...

	jimm

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