Use-positions-properly-dammit hint

[Lubos Lunak <l lunak suse cz>]

 Hello,

 this is basically a followup to the "USPosition vs. PPosition with Virtual 
viewports" thread, this time with a patch :).

 To quickly sum up: Some apps abused PPosition, so WMs started to ignore 
PPosition. So apps moved onto abusing USPosition. So basically now it's a big 
mess with many windows having PPosition|USPosition and WMs having no idea if 
the app just happens to be stupid or if it really has a good reason for that.

 The solution :) :

_NET_WM_FULL_PLACEMENT [*]

By including this hint in _NET_WM_SUPPORTED_LIST the Window Manager announces 
that it performs reasonable window placement for all window types it supports 
(for example centering dialogs on the mainwindow or whatever handling the 
Window Manager considers reasonable). This in turn means that Clients[**], 
when they detect that this hint is supported, SHOULD NOT abuse or often even 
use PPosition and USPosition hints for requesting placement. In particular:
- USPosition is reserved to be used only to indicate that the position was 
specified by the user and MUST NOT be used for anything else (see ICCCM 
section 4.1.2.3 for details)
- PPosition SHOULD be used for for specifying position only if a specific 
position should be used. Position SHOULD NOT be specified for "default" 
placement such as centering dialog windows on their mainwindow.

Rationale: Window managers can often perform better placement (that may be 
even configurable) for windows than the application. However at the time of 
writing this it is problematic for Window managers to decide when to use them 
because many applications abuse positioning flags and/or provide unnecessary 
default positions.

[*] Suggestions for a better name are welcome
[**] Question: Should it be also required that Clients set the same hint e.g. 
in their WM_PROTOCOLS (or a newly made hint) to show that they conform? It 
should not be strictly necessary because the WM should be able to simply act 
sanely and only old broken apps (which won't have the support anyway) will 
keep abusing the flags.


 Comment, improvements, objections? I already have some patches for Xinerama 
support developed that use this hint (so there's a working 
implementation :) ).

-- 
Lubos Lunak
KDE developer
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