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From: shanega@athena.mit.edu (Shane G. Artis)
Newsgroups: comp.sys.next
Subject: Software Development
Summary: BitmapImageRep can't capture off screen
Message-ID: <1991May22.224125.25693@athena.mit.edu>
Date: 22 May 91 22:41:25 GMT
Sender: shanega@athena.mit.edu
Distribution: comp.sys.next
Organization: Massachusetts Institute of Technology
Lines: 41


Hi.  I am having some appkit programming difficulties.  Does anyone
have a good answer for this one?

I am having a problem using a NXBitmapImageRep object to capture portions
of an already drawn View.  What I do is use a code fragment such as:

        tempbm = [[NXBitmapImageRep alloc] initData:tempdata fromRect:&aRect];

        tempimage = [[NXImage alloc] initSize:&aRect.size];

        [tempimage useRepresentation:tempbm];

to capture a rectangle from inside a window into a NXBitmapImageRep object,
and hence to an NXImage object.  Later in the code I redraw this
image using:

        [tempimage composite:NX_COPY toPoint:&aPoint];

This procedure worked fine.  Unfortunately, eventually I had the
window that contained the View partially off-screen, and when I went
to capture an image that was completely off-screen I got a message
from the window server:

        Inconsistent set of values to create NXBitmapImageRep

This was all that was printed, and when the code went to redraw the image
no image was drawn.

If the captured image is partially on-screen then the image appears to get
redrawn to the wrong location.  I need to study this a little more to 
find out the correlation between partially off-screen image capture and
incorrect redrawing.

Does anyone know of a reasonable solution to this problem?  It doesn't
seem to me that when using a Buffered window that NXBitmapImageRep should
care whether I am drawing partially off-screen or not.

Thanks,

Shane