LibGfx/JBIG2+Tests: Add support for refining page contents #26410
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No behavior change.
This was blocked on not having test files. We're about to teach the writer to generate test files and to add test files, so we can add support for this now :^)
No behavior change.
...and add some spec comments. No behavior change.
The page refinement code will have to apply a crop to the page buffer. With this, that's easy to do. No behavior change.
Encoding a generic refinement region that refines the page contents requires that the writer has access to the current page contents. For some region types (text, halftone), computing the output bitmap isn't trivial, and handling all the composition operators and so on is also not trivial. Reimplementing all this in the writer doesn't seem ideal. So instead, when encountering a generic refinement region refining the page contents in the writer, collect the encoded segment data for all segments for the current page (and for the "global page" 0) that are in front of the refinement region, and call into the *loader* to decode the data so far, and then refine the bitmap returned by the loader. This requires storing the encoded data for each segment, but we do that already for implementing writing files in random access organization. It also requires making the list of segments available on JBIG2EncodingContext.
The decode ok in Preview.app, Acrobat Reader, poppler, and HEAD PDFium.
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Similar to SerenityOS#26410, the challenge with refining halftone and text regions is that the writer needs to know the decoded halftone and text region bitmap. That data is easily available in the loader, but not in the writer. Similar to SerenityOS#26410, the approach is to call into the *loader* with a list of segments needed to decode the intermediate region's data. ...and then some minor plumbing to hook up the intermediate region types in jbig2-from-json. With this, we can write all region segment types :^)
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Similar to #26410, the challenge with refining halftone and text regions is that the writer needs to know the decoded halftone and text region bitmap. That data is easily available in the loader, but not in the writer. Similar to #26410, the approach is to call into the *loader* with a list of segments needed to decode the intermediate region's data. ...and then some minor plumbing to hook up the intermediate region types in jbig2-from-json. With this, we can write all region segment types :^)
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Encoding a generic refinement region that refines the page contents
requires that the writer has access to the current page contents. For
some region types (text, halftone), computing the output bitmap isn't
trivial, and handling all the composition operators and so on is also
not trivial.
Reimplementing all this in the writer doesn't seem ideal.
So instead, when encountering a generic refinement region refining the
page contents in the writer, collect the encoded segment data for all
segments for the current page (and for the "global page" 0) that are in
front of the refinement region, and call into the loader to decode the
data so far, and then refine the bitmap returned by the loader.
This requires storing the encoded data for each segment, but we do that
already for implementing writing files in random access organization.
It also requires making the list of segments available on
JBIG2EncodingContext.
This approach is O(n^2) in the number of refinement regions encoding the page, but n is usually 0 or 1, and it's also only writing that hits this code path. It doesn't seem worth adding complexity to add a codepath to incrementally draw the segments that are new since last time, and to only pass those.