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This patch implements a heuristics, which enables backing store for some
windows. When backing store is enabled for a window, the window gets a
backing pixmap (via automatic redirection provided by composite extension).
It acts a bit similar to ShadowFB, but for individual windows.

The advantage of backing store is that we can avoid "expose event -> redraw"
animated trail in the exposed area when dragging another window on top of it.
Dragging windows becomes much smoother and faster.

But the disadvantage of backing store is the same as for ShadowFB. That's a
loss of precious RAM, extra buffer copy when somebody tries to update window
content, potentially skip of some frames on fast animation (they just do
not reach screen). Also hardware accelerated scrolling does not currently
work for the windows with backing store enabled.

We try to make the best use of backing store by enabling backing store for
all the windows that are direct children of root, except the one which has
keyboard focus (either directly or via one of its children). In practice this
heuristics seems to provide nearly perfect results:
 1) dragging windows is fast and smooth.
 2) the top level window with the keyboard focus (typically the application
    that a user is working with) is G2D accelerated and does not suffer from
    any intermediate buffer copy overhead.
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

With the fallback to CPU backend for unsupported blits and also
threshold for avoiding small blits, now G2D should always provide
best overall performance.

The users of recent versions of xf86-video-sunxifb are supposed
to also have a reasonably recent version of linux-sunxi kernel.
Which includes the following fix:
  https://github.com/linux-sunxi/linux-sunxi/commit/3d49345343a1535b



The users of old kernels are going to see screen corruption on
dragging windows and scrolling. They just should upgrade :)
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

This initial G2D support code can speed up moving windows in XFCE. Currently
disabled by default, but can be enabled by editing /etc/X11/xorg.conf and
adding the following line to the "Device" section:

        Option          "AccelMethod" "G2D"
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

The driver can use sunxi display controller layers for fully visible
windows, avoiding expensive memory copy.

Hardware cursor is necessary because it is also visible on
top of sunxi disp layers, while software cursor is not.

FIXME: there is one minor problem with negative cursor
positions. The hardware does not support them, so such
positions are just set to 0 for now. In the future this
can be solved better by changing the cursor picture and
showing only the parts which are visible on screen.

As there is no way for the hardware specific bits to be accepted
in xf86-video-fbdev, we need a new driver with its own name.

It got removed in server's 9727db88d57089be6483104de435626cdbad883a
(long time ago).
Signed-off-by: Cyril Brulebois <kibi@debian.org>
Reviewed-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Julien Cristau <jcristau@debian.org>

Signed-off-by: Jesse Adkins <jesserayadkins@gmail.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>