Add tagged content support inside transparency group XObjects#337
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dcalvo wants to merge 1 commit into
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Add tagged content support inside transparency group XObjects#337dcalvo wants to merge 1 commit into
dcalvo wants to merge 1 commit into
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Per ISO 32000-2 §14.7.4.4.2, Form XObjects created by push_opacity, push_mask, and push_isolated now participate in the structure tree. Each sub-builder gets its own MCID counter and XObjectTagId. Structure elements reference XObject content via MCR dicts with /Stm pointing to the XObject stream. XObjects with tagged content get /StructParents entries in the parent tree.
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Sorry, I haven't had the head space for krilla PRs recently, will try to take a look once I have a bit more time for that. 🙏 |
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This one is pretty chunky, sorry for opening so many PRs at once 😅 This is the last of the changes we've been carrying in our fork, happy to iterate on any of them. We're holding back a custom XMP callback PR for now.
When
Surfacecreates sub-builders for transparency groups (push_mask,push_opacity,push_isolated), the resulting Form XObjects don't carry/StructParentsentries. Anystart_tagged/end_taggedcalls inside the group emit BMC/EMC markers into the XObject's content stream, but those MCIDs aren't connected back to the page's parent tree. Tagged content inside transparency groups is invisible to the structure tree.As noted in #313, this makes it impossible to produce correct tagged output when content sits inside transparency groups.
The fix:
XObjectTagIdand inherit the parent's page indexstart_taggedin a sub-builder allocates MCIDs from the XObject's own counter/StructParentskey