Add optional_content() context manager for screen-only / print-only content#1870
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eugen-goebel wants to merge 3 commits into
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Add optional_content() context manager for screen-only / print-only content#1870eugen-goebel wants to merge 3 commits into
eugen-goebel wants to merge 3 commits into
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Closes py-pdf#441. Adds an FPDF.optional_content() context manager that places the content drawn inside it in a PDF Optional Content Group (a "layer"), with independent on-screen and in-print visibility. This covers the screen-only and print-only images requested in the issue, and works for any content, not just images: with pdf.optional_content(on_print=False): pdf.image("background.png", x=0, y=0, w=pdf.epw) Implementation: - PDFOptionalContentGroup objects carrying a /Usage view/print state - /OCProperties in the document catalog, with an /AS usage-application array that toggles groups for the View and Print events - a /Properties entry in each page resource dictionary - an /OC marked-content sequence around the grouped content Includes a reference-PDF test, a CHANGELOG entry and a documentation page. Based on a recipe by @digidigital.
Optional Content Groups are intentionally not PDF/A-compliant, so the check-reference-pdf-files VeraPDF step flags test/optional_content.pdf. This is handled the same way as fpdf2's other non-PDF/A features.
andersonhc
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Jun 25, 2026
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Thank you for the contribution.
Please see the comments.
| self.struct_tree_root: Optional[PDFObject] = None | ||
| self.a_f: Optional[str] = None | ||
| self.page_labels: Optional[str] = None | ||
| # snake_case "o_c_properties" serializes to "/OCProperties" (cf. a_f -> /AF): |
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I don't think this comment is necessary.
The serialization conversion happens for every field and is commented on the syntax.py classes.
| "6.1.10-1": "REASON: fpdf2 wants to support LZWDecode filter", | ||
| "6.1.11-1": "REASON: /EF is allowed in order for fpdf2 to be able to embed files", | ||
| "6.1.11-2": "REASON: /EmbeddedFiles is allowed in order for fpdf2 to be able to embed files", | ||
| "6.1.13-1": "REASON: fpdf2 supports Optional Content Groups (layers) via FPDF.optional_content(), which are not permitted in PDF/A", |
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That's interesting. PDF/A-1 prohibits optional contents - while PDF/A-2 and later ones allow it.
Can you make it raise PDFAComplianceError on optional_content() if the user selected PDFA/1?
Also add some tests in test/pdf-a.
Optional content is prohibited in PDF/A-1 but permitted from PDF/A-2 onwards, so optional_content() now raises PDFAComplianceError only when the document enforces PDF/A-1. Adds tests for the PDF/A-1 rejection and for PDF/A-2 still being allowed, and drops a redundant comment.
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Thanks for the review. Both points are addressed in the latest commit:
I kept the |
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Link to issue
Closes #441.
Description of change
Adds an
FPDF.optional_content()context manager that places the content drawn inside it in a PDF Optional Content Group (a "layer"), with independent on-screen and in-print visibility. This covers the screen-only / print-only images requested in the issue, and works for any content, not just images.As discussed with @andersonhc in the issue, I went with the context-manager approach (more flexible than an
image()argument, and it keeps the implementation simple). Under the hood it adds Optional Content Group and Usage objects, a/Propertiesentry in the page resource dictionary,/OCPropertiesin the document catalog (with an/ASusage-application array for the View and Print events), and an/OCmarked-content sequence around the grouped content. The minimum PDF version is raised to 1.5.Demo
Testing strategy
Adds
test/test_optional_content.pywith a reference-PDF test (assert_pdf_equal) rendering screen-only, print-only and always-visible content in one document. Documents without optional content are byte-identical to before.Checklist
docs/folderCHANGELOG.mdBy submitting this pull request, I confirm that my contribution is made under the terms of the GNU LGPL 3.0 license.