Re: [gtk-list] Re: Image in a drawing area to .xpm

[Havoc Pennington <rhp zirx pair com>]

On Tue, 1 Jun 1999, Michael J. Hammel wrote:
> Thus spoke Havoc Pennington
> > The X server just throws away the obscured parts - that's why you have to
> > refresh the drawing area when you get expose events. So there's no way to
> > get those pixels since they aren't stored.
> 
> Isn't that whay overlay planes are for?  Xi supports them already, and I've
> been told XFree and Metro are working on it (don't know about the
> workstation vendors, but suspect SGI already supports it).  However, apps
> have to specifically make use of it.  To my knowledge, very few on Linux
> do.  
>

Planes aren't the same as windows. Each window would have its own planes,
possibly including overlay planes. At least as far as I know, I don't know
any details about overlay planes.
 
> Anyone know if Gtk is likely to support overlay planes in the future?
> 

Like all free software projects: if the patches appear. :-)

> > If you're keeping a backing pixmap, you could use that though.
> 
> I think you can also turn on backing store for the server, but that may not
> actually solve the original posters problem.

It's just fundamentally wrong to try to get pixels from a window on the
screen unless you know it's visible; the Xlib API doesn't guarantee that
you can do this.

If you think about it, if the X server was storing the contents of every
window it would chew up truly massive amounts of RAM. 

Havoc