Don't toolkits using many (sub-)windows hurt composite?

Aaron Plattner aplattner at
Tue Aug 15 13:24:13 PDT 2006

On Tue, Aug 15, 2006 at 11:46:44AM +0200, Clemens Eisserer wrote:
> Hi there,
> As far as I know there are 2 different way (maybe even more ;) ) to
> design a toolkit from ground up. Only request one top level window and
> do all layouting/repainting stuff yourself or use X11' sub-windows, so
> X11 handles clipping, event delevery, repainting for your.
> As far as I know the second approach is the one X11 was more or less
> "designed" for and is used by GTK and some other toolkits. (Well GTk
> uses a mixed modell).
> I wonder how the "x11 subwindow model" could be mapped efficiently to
> an X server which runs a composition manager? I ran gftp with a
> modified gtk version (which allocates a pixmap per window instead of
> each repaint) and the result where 15mb of pixmaps allocated for a
> maximized window (1024x680) and its subwindows. According to "xrestop"
> Eclipse itself consists of 315 sub-windows, so I assume about 30-60mb
> of pixmaps.
> As far as I understand when running a composition manager the content
> of each window is stored in pixmaps - however when using sub-windows
> most of of these pixmaps are quite likely hidden by other sub-windows.
> Are there special techniques to avoid this problem. Are there any
> recommandations how toolkits should be designed nowdays?
> Thank you in advance, lg Clemens

Hi Clemens,

Unless some of the subwindows use a 32-bit visual and others don't, the whole
window tree will be redirected into a single pixmap.

-- Aaron
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