Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!eecae!tank!ra_robert@gsbacd.uchicago.edu
From: ra_robert@gsbacd.uchicago.edu
Newsgroups: comp.sys.mac.programmer
Subject: Role of VisRgn Clipping when drawing to Offscreen BitMaps
Message-ID: <2450@tank.uchicago.edu>
Date: 25 Mar 89 03:06:20 GMT
Sender: news@tank.uchicago.edu
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Organization: University of Chicago Graduate School of Business
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I have another offScreen BitMap question.  I want to draw directly to the
offscreen bitmap (OSBM) in a position whose coordinates in the  OSBM's
coordinate system are greater, horiz and/or vert, than the bounds of my
FrontWindow's portRect.  I use SetPortBits to stick my OSBM into my current
window for drawing.  It took me awhile to figure this out, but my drawing there
is being clipped (as far as I can tell) to my FrontWindow's visRgn, which is
also the portRect.  

OK, so I set up another GrafPort  simply for drawing into my OSBM, SetPort to
that, and then SetPortBits my OSBM into this new port.  According to IM 1,
p.149, "the visRgn has no effect on images that aren't displayed on the
screen".  But my drawing in the OSBM still seems to be clipped to my new port's
visRgn, which is now screenBits.bounds (e.g. I need to access vert coordinates
up to 720, and my screenBits.bounds.bottom is 480).  Should I just change the
visRgn?  If I'm drawing offscreen, why doesn't it ignore the visRgn, like IM 1
says?  I suppose I'm missing something, and this is really simple, but...

Any info -- posted or e-mailed -- much appreciated.

Thanks, 
Robert
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ra_robert@gsbacd.uchicago.edu
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generic disclaimer: all my opinions are mine