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Printing Backend Policy

Generated UTC: 2026-06-28

Issue: #529

Current State

PdfBox.Net.Printing.PDFPrintable and PDFPageable remain the Java-shaped printing model classes. They are platform-neutral and keep the upstream scaling, orientation, page-format, and raster-DPI behavior.

PDFPrinter is now a core coordinator rather than a platform print implementation. It validates common printer settings, snapshots them into a PDFPrintJob, and delegates to either its per-instance PrintBackend or the registered PrintingBackend.Current.

Backend Boundary

Core PdfBox.Net owns:

  • PDFPrinter
  • PDFPrintJob
  • IPDFPrintBackend
  • PrintingBackend
  • the unsupported default backend, which throws a clear PlatformNotSupportedException

Optional backend packages own platform submission. The first concrete backend is PdfBox.Net.SystemDrawing:

  • SystemDrawingPrintBackend submits pages through System.Drawing.Printing
  • it is Windows-only
  • it does not replace the rendering backend
  • callers should register a complete rendering backend, currently PdfBox.Net.SkiaSharp, before printing real pages

Capability Matrix

Area Status
Core printing API Available on all supported .NET platforms.
No-backend behavior Fails clearly with guidance to register an optional backend.
Windows printer submission Implemented by PdfBox.Net.SystemDrawing through System.Drawing.Printing.
Windows print-to-file Supported when the configured printer driver supports print-to-file.
Cross-platform printer submission Not implemented yet; add a new IPDFPrintBackend implementation without changing core.
Full page rendering for print Supplied by the registered rendering backend; use PdfBox.Net.SkiaSharp today.

Test Coverage

  • Core tests cover default unsupported behavior and deterministic print-to-file delegation through a fake backend.
  • SystemDrawing tests cover Windows backend registration.
  • Real printer integration remains environment-gated because CI cannot assume a configured printer device or PDF/XPS print driver.

Follow-Up Guidance

Future print backends should implement IPDFPrintBackend in optional packages and register themselves through PrintingBackend.Register(...). Keep platform types out of core PdfBox.Net unless they are already part of a separate, documented Java-shaped proxy layer.