[geeks] nVidia 8800GT for Apple Mac Pro

der Mouse mouse at Rodents.Montreal.QC.CA
Wed May 21 21:22:14 CDT 2008


>> Of course I'm glossing over the effect of "please redraw your
>> windows now please" which is how (I think) X handles off-screen
>> windows.
> I believe that "please redraw your windows now please" is how
> traditionally off screen windows were handled by window managers that
> supported off screen windows.

Ummm...unless you're talking about X specifically on the Mac (and even
then, it would be implementation-dependent), this betrays an ignorance
of how X handles window redrawing, including redrawing of window
portions formerly off-screen but now on-screen.

Window contents are not necessarily maintained when a window is not
viewable ("viewable" is a technical term that, for our purposes here,
we can read as "on-screen").  If window contents _are_ maintained then,
where they are maintained is up to the server.  If it happens to find
it convenient to leave them in graphics-card memory, it's welcome to,
as far as X is concerned.

There is an event type, Expose, which is sent by the X server to tell a
client "this portion of this window needs drawing"; this is about as
close to "please redraw your window now" as X has.  This can happen
because the window has never been drawn before, because that window
portion (which may be the whole window) was formerly not on the screen
but now is, because that window portion formerly had something in front
of it but now doesn't, etc.  Servers usually will not maintain the
contents of unviewable windows or window portions (though it's
permitted to, and there's a hint clients can provide to say it's likely
to be a good idea).

Strictly, the window manager has nothing to do with this.  It's usually
what's responsible for shifting windows between on- and off-screen, but
it doesn't handle telling clients they need to redraw per se.

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