We no longer have to turn the client's content into an image buffer "by hand".
Instead, we can just use cairo for the job.
Even more exciting, we don't need to turn this into an image buffer at all. We
can just directly return a cairo xcb surface for the client window. Depending on
how lua will use this surface, this could make it possible to avoid having to
create the image buffer at all!
Signed-off-by: Uli Schlachter <psychon@znc.in>
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