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From: pepke@loligo.cc.fsu.edu (Eric Pepke)
Newsgroups: comp.sys.mac.programmer,comp.sys.mac
Subject: Re: CopyBits in MPW C 3.0
Keywords: CopyBits , MPW C
Message-ID: <580@loligo.cc.fsu.edu>
Date: 13 Apr 89 14:30:44 GMT
References: <225@uw-apl.UUCP> <98709@sun.Eng.Sun.COM>
Reply-To: pepke@loligo.UUCP (Eric Pepke)
Distribution: na
Organization: Supercomputer Computations Research Institute
Lines: 42

In article <98709@sun.Eng.Sun.COM> wert@sun.UUCP (Robert Scott Comer) writes:
>Here is how you fix that: Look for the definition of CopyBits. See that first
>parameter? See its type? Determine what that type is, exactly, then make sure
>you pass that type in to CopyBits.
>
>For example, if CopyBits wants a pointer to a BitMap or PixMap, then what you
>have looks like it might work, if it wants a handle to one of those you will
>have to remove the * from your first argument.

If you are going to condescend, at least make sure you know what you're
talking about.

OF COURSE CopyBits wants a pointer.  The problem is that the C prototype
wants a pointer to a BitMap, not to a PixMap.  There are a number of ways
of constructing the type cast which can seem to a novice as if they should 
work, but not all of them do.

This code fragment compiles fine under my MPW 3.0 C:

	WindowPtr wind;
	PixMapHandle mypixhandle;

	HLock((Handle) mypixhandle);
	CopyBits(*(BitMap **) mypixhandle, &(wind->portBits),
            &((*mypixhandle)->bounds),&((*mypixhandle)->bounds),
            srcCopy, 0L);
	HUnlock((Handle) mypixhandle);

Notice that the casting of the window to type GrafPtr is not needed.  As 
explained in IM, a WindowPtr is the same as a GrafPtr, and to look in the 
extra fields in a window record, use a WindowPeek type cast.  This is not 
the case for BitMaps and PixMaps, so the cast to BitMap ** is needed.

C and Pascal are becoming more and more alike as time goes on.  :-(

Eric Pepke                                     ARPA:   pepke@gw.scri.fsu.edu
Supercomputer Computations Research Institute  MFENET: pepke@fsu
Florida State University                       SPAN:   pepke@scri
Tallahassee, FL 32306-4052                     BITNET: pepke@fsu

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