Bill Crawford billcrawford1970 at
Thu Apr 9 03:03:16 PDT 2009

On Thursday 09 April 2009 10:39:47 Alan Cox wrote:
> > > if someone massively resizes a window with backing store (remembering
> > > it can be mostly offscreen) your X server explodes.
> >
> > Remind us why turning it on for all windows all the time (Composite) is
> > better than for one window? ;o)
> There is nothing in composite that requires you redirect everything.

I know, I'm just remembering the first time I tried turning compositing on and 
suddenly everything slowed to a crawl (the windows I had on the screen used 
more memory than there is on the graphics card, and I suspect everything was 
being kept in system memory at that point).

> > > Backing store was mostly a mistake at the time of introduction (as
> > > opposed to save unders which are a least reasonably resource bounded).
> >
> > It was overused, sure, but the idea suggested elsewhere in the thread of
> > using a pixmap and setting that as the window background is essentially
> > doing the same thing (a form of double buffering).
> Without all the horrendous complexity and bugs that save unders caused.
> The fact you can do it better other ways is even more argument for the
> fact they are no longer on. (Not that save unders actually worked
> properly in most XFree/Xorg releases in all cases)

Yeah, the "bugs" part is understood. I think the frustration for some people is 
that they are being told Composite will replace the functionality of backing 
store, but haven't been given an implementation for a while ...

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