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From: aw@jello.bae.bellcore.com (Andrew Wason)
Newsgroups: comp.windows.x
Subject: Re: Resource Cvt*To* reoutine problem
Message-ID: <1991Apr17.181741.7865@bellcore.bellcore.com>
Date: 17 Apr 91 18:17:41 GMT
References: <9104162110.AA25496@gothamcity.jsc.nasa.gov>
Sender: usenet@bellcore.bellcore.com (Poster of News)
Reply-To: aw@bae.bellcore.com
Organization: Bell Communications Research
Lines: 44

In article <9104162110.AA25496@gothamcity.jsc.nasa.gov>, bill@gothamcity.jsc.nasa.GOV (Bill Shirley [CSC]) writes:
> 
>  Q: I am writing a resource conversion routine.  How can I call an Xt 
>  conversion routine from my converter?  There are, basically, two functions
>  to call converters with: XtCallConverter (XtDirectConvert in R3), and 
>  XtConvertAndStore (XtConvert in R3).
> 
>   XtCallConverter needs the pointer to the function.  The Xt Cvt functions,
>  in Convert.c, are defined statically and thus their pointers aren't 
>  available.

You mean Converters.c.

>   XtConvertAndStore takes a Widget as a parameter.  There is not a Widget to
>  use in my conversion routine.  I tried passing a pointer to the core.self
>  field as a parameter and then casting this into a Widget (it is the first
>  field of the instance structure of all Widgets).  This gave my the lovely 
>  result of a 'Bus error'.

I'm not sure what the correct solution is, but take a look at
XmuCvtStringToCursor() in lib/Xmu/StrToCurs.c.  It needs to invoke
the StringToFont converter.
It does the following (old style interface):

        WidgetRec widgetRec;

        [...]

        /* widgetRec is stupid; we should just use XtDirectConvert,
         * but the names in Xt/Converters aren't public. */
        widgetRec.core.screen = screen;
        fromString.addr = source_name;
        fromString.size = strlen(source_name);
        XtConvert(&widgetRec, XtRString, &fromString, XtRFont, &toFont);

This seems dangerous, but off hand I can't think of another way.

Andrew

_______________________________________________________________________________

Andrew Wason                                       Bell Communications Research
aw@bae.bellcore.com                                Piscataway, NJ
bellcore!bae!aw