The filter picked its output format in config_props(), after format
negotiation had already settled the output link. The frames it emitted
could therefore disagree with the negotiated link format, for example
when a downstream zscale had negotiated something else.
Switch to FILTER_QUERY_FUNC2() and decide the output format during
negotiation instead:
- with format=, the output is constrained to that single format, which
is now also validated in init() against the supported output list;
- otherwise, when no half-float candidate remains on the input, the
output list is the input list, so the filter passes the format
through and downstream constraints can still narrow the input;
- otherwise the output is restricted to float, and negotiation picks
GBRPF32 or GBRAPF32 to match the input's alpha.
Half-float input has to be promoted because swscale cannot read or
write half-float in its new backend, and its legacy code clamps
half-float to [0,1], which would destroy values outside that range.
Half-float is therefore no longer offered as an output format.
The default output depends on the input format, so the query waits for
the input list to be merged with the upstream one, which it detects by
comparing it against the input link's other end. The merged list need
not be a singleton. Waiting for a singleton would reject valid graphs,
because a filter such as zscale offers half-float and integer formats
on its output independently of its input, so that list never narrows
to one of the two.
While the query is delayed it publishes the input color space, color
range, alpha mode and chroma location lists, because a converter
inserted on the input requires them, but the matching output lists are
only published together with the output pixel formats, as a converter
inserted on the output would otherwise find them without a format list
and crash.
Finally, supply opaque input alpha when the output format has alpha and
the input format does not. Prepend an alpha-initialization matrix to the
resolved OCIO processor, allowing OCIO to optimize it with the user's
transform. This avoids a separate per-frame alpha fill and ensures that
transforms which use alpha in RGB calculations or modify alpha receive
the opaque value before processing and retain their transformed alpha.
Filling output alpha after processing would instead leave alpha-dependent
RGB incorrect and overwrite alpha produced by the user's transform.
Note, this includes Fairys fairy/pr21799-replace patch (Thank-you Fairy!).
Signed-off-by: Sam Richards <Sam.Richards@taurich.org>
Assisted-by: Fairy
