Rootless layer plans

[Torrey Lyons]

Here's an overview of the development plans for the generic rootless 
layer (see Xserver/miext/rootless) before the next major release. The 
users of this code that I know about are Mac OS X and Cygwin, but any 
comments and questions are welcome.

1. Add support for "fullscreen rootless" mode. In fullscreen rootless 
mode, the X server looks like a normal X server as the root window is 
drawn and covers the rest of the native window system. One can 
dynamically switch back and forth between true rootless mode and 
fullscreen rootless mode. This is useful for users who need to see or 
interact with the root window or those who want a more immersive X11 
experience (such as it is). Implementations should not have to do 
much to support this mode. They mostly just tell the rootless layer 
when to switch based on some implementation specific signal 
(typically a key sequence).

2. Make rootless fully interoperate with Damage and Composite. 
Rootless almost works completely with Damage. It currently does not 
damage regions it should in every case. Composite does not really 
work, but there are are two separate issues here:

a) Rootless currently relies on the underlying window system to 
provide an off screen buffer for each of its top level windows. If 
the window system does not do this, the implementation has to do it. 
Perhaps Composite could be used instead to do this if the underlying 
window system can't. (If the window system can do something, it is 
more efficient to let it do it itself.)

b) When using the underlying window system for off screen buffers, 
the Composite extension should be made to "work" as viewed from the 
client side.

FWIW, once #1 is completed we will have completed merging in 
everything from Apple's X11 source code 
<http://www.apple.com/macosx/features/x11/>. The features of X.Org 
will be a superset of Apple's X11.

--Torrey