Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!intercon!amanda@mermaid.intercon.com
From: amanda@mermaid.intercon.com (Amanda Walker)
Newsgroups: comp.sys.mac.programmer
Subject: Re: List Bummers Revisited
Message-ID: <1622@intercon.com>
Date: 13 Dec 89 16:28:00 GMT
References: <cZVSJ9i00WB2Q63mcX@andrew.cmu.edu>
Sender: news@intercon.com
Reply-To: amanda@mermaid.intercon.com (Amanda Walker)
Lines: 79

In article <cZVSJ9i00WB2Q63mcX@andrew.cmu.edu>, es2q+@andrew.cmu.edu (Erik
Warren Selberg) writes:
> Is there any way to access
> variables in the main program from an LDEF, and if so, how??!

Well, they way I do it is to have a baby LDEF that, by default, just
draws a string they way LDEF 0 does, but if the list's refCon is non-zero,
treats it as a pointer to a function and calls it to do the drawing.
All you have to do is make sure A5 is set correctly.

Here's the source for the LDEF in MPW C 3.0, taken in its entirety
from known working code.  It does contain "the cast from Hell," but hey :-).

----------------------
/*
    Simple Custom LDEF

    Amanda Walker, InterCon Corporation
    6 October 1988

    This is a very simple custom LDEF.  It acts just like LDEF 0 if the refCon
    field of the list is 0.  If it is non-zero, the LDEF treats it as the
    address of a routine to call to actually draw a list element.

*/

#include <Quickdraw.h>
#include <Lists.h>
#include <OSUtils.h>

#define nil ((void *) 0L)

pascal void STUBLDEF(lMessage, lSelect, lRect, lCell, lDataOffset, lDataLen,
		     lHandle)
short lMessage;
Boolean lSelect;
Rect *lRect;
Cell *lCell;
short lDataOffset, lDataLen;
ListHandle lHandle;
{
    char *p;
    long savedA5;
	
    /* Make sure A5 is valid so the draw code can use its globals. */
    savedA5 = SetCurrentA5();

    p = (char *) 0x938;		/* HiliteMode for color QD */
    lMessage--;			/* no initialization */
    if (!lMessage--) {		/* draw the cell */
	if ((**lHandle).refCon)
	    (*((pascal void (*)(Rect *, Cell *, short, short, ListHandle))
		(**lHandle).refCon))(lRect, lCell, lDataOffset, lDataLen,
				     lHandle);
	else {
	    MoveTo(lRect->left + 5, lRect->top + 12);
	    HLock((**lHandle).cells);
	    DrawText(*((**lHandle).cells), lDataOffset, lDataLen);
	    HUnlock((**lHandle).cells);
	}
	if (lSelect) {
	    *p = *p & 0x7f;
	    InvertRect(lRect);
	}
    } else if (!lMessage--) {	/* toggle highlighting */
	*p = *p & 0x7f;
	InvertRect(lRect);
    }
    SetA5(savedA5);		/* no closing code */
}
----------------------
If you don't know how to build code resources with MPW C, take a look
at the examples in the CExamples directory.

Hope this helps,

Amanda Walker
InterCon Systems Corporation
--