This new helper assists compositors in allocating buffers for
modesets. It degrades to different allocation parameters as
needed, and should help with screens not turning on when multiple
outputs are connected on some hardware (e.g. Intel).
For simplicity, the old logic to try allocating with explicit
modifiers first and then fallback to implicit modifiers later is
left as-is. We'll probably want to have more complicated logic
instead in the future: try the fallback on one output at a time,
and try dropping modifiers one by one instead of using implicit
modifiers (at the cost of some combinatorial explosion).
Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/1873
Co-authored-by: Kenny Levinsen <kl@kl.wtf>
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