FR-RAW-2 says a second decoder may be added for broader camera coverage
without changing callers, and D2 names LibRaw as that second decoder.
Nothing tested the claim: dr_decode was one decoder reached through free
functions, so adding another would have meant editing every caller at
the moment there was most pressure not to.
Decoder is an object-safe trait over bytes: header_bytes, metadata,
orientation, locate_preview, preview and decode. Rawler implements it by
delegating to the existing free functions, so behaviour is unchanged,
and dr_decode::default() hands it out as a &'static dyn Decoder, which
is what the places that start work will name. JPEG recognition, decoding
and completeness checks stay free functions: they are not a RAW
decoder's to vary.
Nothing in the trait takes a path or a SourceRef; the decoder states how
much of a file it needs and where its preview sits, and the caller's
storage fetches that.
dtourolle
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