- From: "Ryan C. Gordon" <icculus icculus org>
- To: wm-spec-list gnome org
- Subject: Proposing _NET_WM_STATE_FULLSCREEN_EXCLUSIVE
- Date: Tue, 23 Oct 2012 16:26:20 -0400
I've been doing Linux video games for over a decade now, and we've never
really had a satisfactory means to handle fullscreen games on X11. I see
this mailing list discussed fullscreen problems briefly in February, but
I wanted to make a formal proposal of how the system should handle
applications that want to "go fullscreen."
This is a first draft that Sam Lantinga and I put together, envisioning
how we would like SDL to cooperate with the Window Manager to solve the
Being a first draft, anything that's silly is totally open to change. We
have an SDL patch that implements the client side of this spec, but no
one's tried to implement the Window Manager side of things yet.
Comments and criticism are appreciated!
This is an addition to the spec for _NET_WM_STATE:
There are some problems with the current _NET_WM_STATE_FULLSCREEN hint
that we would like to address.
First, it is not explicit in its instructions to Window Managers; for
example, we found some Window Managers required the window to be marked
resizable (Metacity) and others did not (XFCE); it's not clear which is
correct. It doesn't address virtual desktop size verses physical
resolution. This proposal tries to be very clear about exactly what
steps are required.
Second, the window manager needs to be responsible for changing
resolutions. If an app tries to use XVidMode, the virtual desktop will
not be resized and _NET_WM_STATE_FULLSCREEN will size the window
incorrectly. If an app instead tries to use XRandR, the rest of the
desktop may change irreversibly; icons may move around, other app
windows may shrink down. Worse still, if an app changes the resolution
with XVidMode or XRandR and then crashes before cleaning itself up, the
desktop will remain in the wrong state until the user takes heroic
measures to fix it. Moving this operation into the Window Manager and
associating it with a specific window lets the system know that this is
a temporary state change, instead of two discrete actions that may be
unrelated, so that it can protect desktop state appropriately. This also
has the side benefit of centralizing a complex negotiation with X11
extensions and multiple processes into one place--the Window
Manager--instead of every application.
Certainly _NET_WM_STATE_FULLSCREEN still has a place; it still makes
good sense that the example given, a presentation program, use that
hint. For applications like video games, which need more control over
window geometry and specific screen resolutions, a new hint is extremely
A Window Manager supporting this specification MUST specify
_NET_WM_STATE_FULLSCREEN_EXCLUSIVE in the list of atoms reported by the
(Added to the list of _NET_WM_STATE hints...)
_NET_WM_STATE_FULLSCREEN_EXCLUSIVE indicates that the Window Manager
MUST change the resolution of the window's screen to one that most
closely matches the window's current dimensions. If no available
resolution matches exactly, the Window Manager MUST select the closest
available resolution larger than the window. The Window Manager MUST
center the window within the new resolution, remove any window
decorations, retain its original geometry, and grant that window input
focus. If the chosen resolution does not match the window geometry, the
Window Manager MUST obscure the rest of the screen so that the window is
the only thing visible. If there is no resolution that can completely
contain the window's undecorated geometry, the Window Manager MUST
refuse to allow this hint.
If the window loses input focus while fullscreen, the Window Manager
MUST revert the resolution change and iconify the window until it
regains input focus. The Window Manager MUST protect desktop state (icon
positions, geometry of other windows, etc) during resolution change, so
that the state will be unchanged when the window ceases to be marked as
fullscreen. The _NET_WM_STATE_FULLSCREEN_EXCLUSIVE and
_NET_WM_STATE_FULLSCREEN hints MUST NOT be used together by an
application; in such a case, the Window Manager must reject the
If more than one window on the same screen requests the
_NET_WM_STATE_FULLSCREEN_EXCLUSIVE hint, the latest window MUST obtain
its requested resolution and input focus, and all other windows with
this hint MUST be iconified.
For example, a video game would use this hint.
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