Hello,
How exactly should the BD_OVERLAY_CLEAR and BD_OVERLAY_WIPE commands be
implemented?
The contents of the overlay are 8-bit indexes to a palette. Each pixel
cannot do anything other than reference an entry in the palette but if
the contents of the palette can be set to anything, how can you ensure
that a pixel has been cleared?
The palette could be scanned to find a transparent entry, but is there a
guarantee that at least one entry will be transparent? I could imagine
it's likely but not necessarily guaranteed.
Even if a transparent entry is found, it may not remain transparent if
the palette is updated.
Another way would be to maintain an additional 1-bit mask but that seems
rather inefficient.
As far as I can tell from the code, these two commands are not directly
linked to the structure of a Bluray disc, but have been created as part
of the libbluray implementation.
I'd be very grateful for an explanation of the design considerations
behind these commands (or a pointer to any documentation).
Thanks in advance!
Richard.
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