$ show flytkgl/PDFQFZ
PDFQFZ is a Chinese-language Windows Forms desktop application that overlays seal/stamp images onto existing PDFs, including cross-page seam stamps (éŠįžįŦ ) split across page edges. It supports file/folder batch processing, configurable stamp size/opacity/rotation/placement, white-background transparency removal, PDF password encryption, and optional digital signatures using self-generated or imported PFX certificates. A "merge" mode rasterizes PDF pages at 300 DPI and reconstructs them to flatten content. The app accepts PDF files as command-line arguments and supports drag-and-drop input. The architecture is a single large Form1.cs WinForms monolith for UI and orchestration, with a small Library/ folder of extracted helper classes: a generic PageCache<T> for lazy page preview loading, pure stamp policy predicates, layout calculators, numeric input sanitizers, an async request gate for stale preview cancellation, and an image transparency helper. A separate xUnit test project targets net9.0-windows and compiles linked Library sources to test these helpers, but the main project targets .NET Framework 4.7.2 and is not included in the solution file. The data flow is straightforward: users select source PDFs and a stamp image; pdfGz() iterates files, opens each PDF with iTextSharp PdfReader/PdfStamper, splits the stamp into segments via subImages(), and places them according to seam-stamp mode and position settings. The preview path renders pages lazily through PDFRender4NET at low DPI and uses PageCache plus PreviewOverlayRequestGate to avoid UI hangs on large PDFs. Maintenance is recent and tests exist, but the main application still depends on abandoned/legacy libraries, references an external DLL via an out-of-repo Downloads path, includes committed probe artifacts, and contains a fair amount of monolith-style code debt.
The LLM identified 5 files worth highlighting for reuse:
Generic lazy page cache keyed by int index. Loads pages on demand via a Func<int,T>, caches them in a Dictionary, disposes cached entries on Clear/Dispose, and throws ObjectDisposedException after disposal. Isolated with no internal project dependencies; can be extracted into any .NET app needing lazy resource caching with deterministic cleanup.
Converts near-white pixels to transparent in a copy of a Bitmap using LockBits + Marshal.Copy, preserving source DPI/resolution. Tolerance is clamped to 0-50. Pure System.Drawing dependency; reusable for stamp/logo/watermark preprocessing and other bitmap transparency cleanup tasks.
Calculates rendered overlay size from configured physical width in millimeters, source image DPI and pixel dimensions, preview width, and PDF width. Encapsulates mm-to-point conversion (72/25.4) and aspect-ratio scaling with fallback handling. A small, testable pure function reusable for mapping physical print sizes into screen-space overlays.
A tiny thread-safe gate that issues monotonically increasing request IDs using Interlocked/Volatile so asynchronous UI preview renders can be discarded once stale. No dependencies beyond System.Threading; reusable for any UI that needs latest-request-wins async rendering without heavyweight cancellation plumbing.
Pure string sanitizers for digits-only and signed-integer inputs, plus clamped integer parsing with fallback. Uses efficient character-buffer loops rather than LINQ. Reusable for WinForms/WPF text boxes or CLI argument parsing where invalid numeric input must be normalized safely.