When the new option is enabled, headless backend will draw decorations
around its outputs. This makes the actual "framebuffer" larger by the
thickness of the decorations to keep the video mode area free for
clients.
This will be needed for a future test, that will ensure that GL-renderer
will paint the output decorations correctly.
The output title is deliberately NULL, because text rendering is
unpredictable and depends on e.g. what fonts are installed in the
system. Therefore screenshot testing of any text would be really
painful, so let's avoid that.
The decorations setup code is mostly copied from wayland-backend.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
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