[10026] in The GTK GIMP ToolKit mailing list archive
[gtk-list] Re: Gdk, X11, and backing store
daemon@ATHENA.MIT.EDU (Jeff Garzik)
Wed Nov 11 17:21:13 1998
To: dov@imagic.weizmann.ac.il
Date: Wed, 11 Nov 1998 17:20:18 -0500 (EST)
Cc: gtk-list@redhat.com
Reply-To: jgarzik@pobox.com
In-Reply-To: <199811112207.AAA02146@imagic.weizmann.ac.il> from "Dov Grobgeld" at Nov 12, 98 00:07:11 am
From: Jeff Garzik <jgarzik@pobox.com>
Resent-From: gtk-list@redhat.com
Dov Grobgeld wrote:
>
> I have a question concerned with the lack of backing store in Gdk. I'm
> not a big expert on X, but one of the things that I have picked up is
> that if when you create a window do:
>
> unsigned long valuemask;
> XSetWindowAttributes attributes;
>
> :
> valuemask = CWBackingStore;
> attributes.backing_store = WhenMapped;
> :
>
> win = XCreateWindow(... , valuemask, &attributes);
> XMapWindow(dpy, win);
>
> you no longer get any exposure events for the window, but the X server
> is taking care of the exposure events on its own by using backing_store.
>
> For some reason not totally clear to me, it is much faster to use
> backing store than to do the exposure handling yourself by drawing in
> a pixmap and just copying it when you get the exposure event. I
> suspect that the X-server is using video-memory than is not visible on
> the screen, whereas such memory is not available for a user process,
> but I might be wrong.
I believe that the X server uses server-side resources for the backing
store, as you suspect. If you want to do your own backing store-type
functionality, use XImage*() calls. An XImage is a server-side
resource, whereas (IIRC) a pixmap is a client-side resource.
Server-side versus client-side makes a world of difference in many
situations, especially when running X over a network.
Jeff
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