Niklas Haas authored May 09, 2021 and Hugo Beauzée-Luyssen committed Jun 04, 2021

Recent versions of libplacebo use `pl_frame.crop` instead of
`pl_render_target.dst_rect`, for which the latter is now merely a
fallback.

Unfortunately, `pl_render_target_from_swapchain` ends up setting the
former field to values based on the swapchain dimensions, so the values
we set in `dst_rect` accidentally ended up ignored. In retrospect, this
was caused by the upstream decision to make the new field override the
old field if both are present, and having that logic the other way
around would also have avoided this bug. Bite the bullet and make it
conditional on the PL_API_VER.

All that said - merely fixing this bug, however, exposed serious
shortcomings in the video placement logic, in particular the lack of
proper flipping support for OpenGL. Fix it by rewriting the video
placement logic completely, based on the observation that
`vout_display_PlacePicture` is a relatively cheap function to call.
There's no need to awkwardly cache it inside `sys`.