Re: move/resize handling again

[Dominik Vogt <dominik vogt gmx de>]

On Fri, Nov 15, 2002 at 05:32:59PM +0100, Matthias Clasen wrote:
> On Fri, 2002-11-15 at 11:43, Dominik Vogt wrote:
> > 
> > The description looks good.  I am a bit unhappy that it seems to
> > suggest it is a good idea to change the win_gravity often.  The
> > ICCCM says that the "last" win_gravity is used, but this suffers
> > from the same problem as with the size inc hints we discussed a
> > while ago.  The WM only gets a message that is has changed, but
> > has to look up the value itself.  The hint can already have
> > changed again when the WM gets around looking it up.  E.g.
> > 
> >   - set NW gravity
> >   - moveresize to 100x100+0+0
> >   - set SE gravity
> >   - resize to 50x50
> > 
> > may be read by the WM as
> > 
> >   - set SE gravity
> >   - moveresize to 100x100+0+0
> >   - set SE gravity
> >   - resize to 50x50
> > 
> 
> Would adding a note explaining the race condition help ? Like so:

I think it might even warrant a new paragraph.  Give me a few days
to write something down that explains the proper procedure to
change wing_gravity, the base_... and ..._inc hints.

> 		<listitem><para>
> Applications are free to change their win_gravity setting at any time.
> 		</para>
> 		<para>
> If an Application changes its win_gravity then the Window Manager should
> adjust the reference point, so that the client window will not move as
> the result. For example if the Application's win_gravity was
> NorthWestGravity and reference point was at the top-left corner of the
> frame window, then after change of win_gravity to SouthEastGravity the
> reference point should be adjusted to point to the lower-right corner of
> the frame.
> 		</para>
>                 <note>
>                 <para> 
> Changing the win_gravity for a single configure request and back
> afterwards is unlikely to work as intended, due to a race condition. The
> window manager sees a property notify for WM_NORMAL_HINTS, followed by
> the configure request, followed by another property notify for
> WM_NORMAL_HINTS. By the time the window manager gets around to request
> the changed WM_NORMAL_HINTS in response to the first property notify,
> the server may have already processed the second property change.  
>                 </para>
>                 <para>
> If the window manager supports it, applications should use 
> _NET_MOVERESIZE_WINDOW with a specified gravity to avoid this problem.
>                 </para>
>                 </note>
>                 </listitem>

Bye

Dominik ^_^  ^_^