avfilter/vf_libplacebo: skip rendering fully invisible planes

Sometimes, one input fully obscures another. In this case, we can skip
actually rendering any input below the obscuring one.

The reason I don't simply start the main render loop at `idx_start` will
become apparent in the following commit.

We can't use pl_frame_is_cropped() on this dummy frame, but we need to
determine the reference frame before we can map the real output, so to
resolve this conflict, we just reimplement the crop detection logic using
the output link dimensions.

0 files changed, 0 insertions, 0 deletions