The CoglOutput object represents one output such as a monitor or
laptop panel, with information about attributes of the output such as
the position of the output within the global coordinate space, and
the refresh rate.
We don't yet publically export the ability to get output information but
we track it for the GLX backend, where we'll use it to track the refresh
rate.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit d7ef9d8d71488d0e6874f1ffc6e48700d5c82a31)
