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From: jg@max.crl.dec.com (Jim Gettys)
Newsgroups: comp.windows.x
Subject: Re: X region and its data structure
Message-ID: <298@crltrx.crl.dec.com>
Date: 3 Aug 89 02:49:01 GMT
References: <7133@kuhub.cc.ukans.edu>
Sender: news@crltrx.crl.dec.com
Organization: Cambridge Research Lab, Digital Equipment Corporation
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>1. What is the data structure for X region? 

It is deliberately opaque; i.e. you aren't allowed to find out; it is private
to the library.

>2. I can create a rectangle or polygon region. How can I creat an ellipse
>   region? Do I have to find the edge points for the ellipsefirst and then
>   use XPlolygonRegion?

Unfortunately yes; we didn't have time to implement such a routine before X11R1,
so left it out.

>3. Once a region is set, can I get the region pointer? I mean that I don't
>   know the clipregion and I don't care, but I want to set a new clipmask
>   region by intersecting the current clipmask region with a third region.

Nope.  But you can certainly remember your regions and do the intersection
in the client program with the Xlib routines.  You wouldn't want to query
the server anyway; as usual, never rely on the server for information you could
have remembered in the first place, as it saves round trips.


>4. It is possible to create an arbitrary region by creating a bitmap first
>   But when I set this region, the old clipmask region will be destroyed.
>   Is there a way to keep the old region for later use? ( it is similar to 3)

Again, if you've computed your region in the first place, you should have it
around for later use when you need it.

You could be complaining that there should be an Xlib routine which takes and XImage
structure containing a bitmap and turns it into a region for other Xlib use, and I
wouldn't necessarily disagree with you, and for cleanlyness's sake, there should
probably be such a routine for arcs.  If this is what you need, I suspect you could
get support for it to be added in a future release.  What is in Xlib now is sort
of the least we could get away with in region code, given the initial time pressure of
the first release.  It was nip and tuck getting the original specification implemented
at the time.
				- Jim Gettys