PDF stage 2.3: form XObjects#540
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Parse a resource dictionary's /XObject table and execute `Do` on form XObjects: save state, concatenate the form /Matrix onto the CTM, run the form content against its own /Resources (falling back to the enclosing scope), then restore. Image XObjects are recognized but deferred to stage 4; /BBox clipping is deferred. Form content, /Matrix and nested /Resources are read eagerly at parse time so text extraction needs no parser handle. The parser memoizes XObjects by reference (ObjectReference -> XObject*, registered before recursing), so a form shared across pages is parsed once and a cyclic form reference resolves to the existing element -- the in-memory graph mirrors the file rather than clipping cycles. A render-time active-set guard cuts cyclic invocation (forbidden by ISO 32000-1 8.10.1 but present in real files). Add GraphicsState save()/restore()/concat_matrix(), reused by q/Q/cm. Tests: cyclic /Resources represented faithfully via the cache, a form shared by two pages parsed once, and (page-text) invocation, /Matrix placement, state restoration, scoped resources, nested forms, image/unknown XObjects ignored, and a self-referential form terminating via the active-set guard. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Implements stage 2.3 of the in-house PDF roadmap: form XObjects.
What it does
pdf_document_parser,pdf_document_element): a resource dictionary's/XObjectsubdictionary is parsed intoResources::x_object. Each/Subtype /Formbecomes anXObjectelement carrying its/Matrix(default identity), its eagerly decoded content stream, and its own parsed/Resources(nullptr⇒ inherit the invoking scope). Image XObjects are recognized but deferred to stage 4; unknown subtypes are inexecutable.pdf_page_text):Dosaves the graphics state, concatenates the form/Matrixonto the CTM, runs the form content against the form's resources (falling back to the enclosing scope), then restores — so text inside forms is placed correctly. AddedGraphicsState::save()/restore()/concat_matrix(), reused byq/Q/cm.Cycles & sharing
The parser memoizes XObjects by reference (
ObjectReference → XObject*, registered before recursing into/Resources), so:A render-time active-set guard cuts cyclic invocation. The spec forbids form cycles (ISO 32000-1 §8.10.1), but real files contain them.
Deferred
/BBoxclipping (text-only for now). The form machinery is reused by stage 4 (tiling patterns) and stage 5 (annotation appearances).Tests
/Resourcesrepresented faithfully via the cache (back-edge points at the same element); a form shared by two pages parsed once./Matrixplacement, state restoration, scoped resources, nested forms, image/unknown XObjects ignored, and a self-referential form terminating via the active-set guard.All PDF unit tests + odr-engine PDF end-to-end tests pass locally.