stirling-tools--stirling-pdf
wehub-resource-sync
62 行
2.6 KiB
Markdown
62 行
2.6 KiB
Markdown
# Windows PDF Thumbnail Handler
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A lightweight COM DLL that provides PDF page-preview thumbnails in Windows Explorer when Stirling-PDF is the default PDF application.
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## Why this exists
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When Stirling-PDF registers as the default PDF handler, Windows associates `.pdf` files with Stirling's ProgID. Without a thumbnail handler on that ProgID, Explorer falls back to showing the application icon (the big S logo) instead of a page preview. This DLL restores thumbnail previews by implementing the Windows Shell `IThumbnailProvider` COM interface.
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## How it works
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1. **Explorer requests a thumbnail** — when a folder with PDFs is opened in Medium/Large icon view, Explorer loads the DLL via the registered COM CLSID.
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2. **Shell calls `IInitializeWithStream`** — passes the PDF file content as an `IStream`.
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3. **Shell calls `IThumbnailProvider::GetThumbnail(cx)`** — requests a bitmap of size `cx × cx`.
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4. **The DLL renders page 1** using the built-in `Windows.Data.Pdf` WinRT API (the same engine Edge uses), preserving aspect ratio.
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5. **WIC decodes the rendered PNG** into BGRA pixels, which are copied into an `HBITMAP` via `CreateDIBSection`.
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6. **Explorer displays the bitmap** as the file's thumbnail.
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All COM methods are wrapped in `catch_unwind` so a malformed PDF cannot crash Explorer.
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## Technical details
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| **Language** | Rust (cdylib) |
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| **DLL size** | ~156 KB |
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| **External deps** | None — uses only Windows built-in APIs |
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| **PDF renderer** | `Windows.Data.Pdf` (WinRT, Windows 10+) |
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| **Image decode** | WIC (`IWICImagingFactory`) with BGRA32 format conversion |
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| **COM CLSID** | `{2D2FBE3A-9A88-4308-A52E-7EF63CA7CF48}` |
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| **Threading model** | Apartment (STA — standard for shell extensions) |
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| **Min Windows** | Windows 10 |
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## Registry entries (managed by MSI)
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The WiX installer (`provisioning.wxs`) registers:
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- **CLSID** at `HKLM\SOFTWARE\Classes\CLSID\{2D2FBE3A-...}\InprocServer32` pointing to the DLL
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- **Shellex** at `HKLM\SOFTWARE\Classes\.pdf\shellex\{E357FCCD-...}` linking `.pdf` thumbnails to our CLSID
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Both are automatically removed on uninstall.
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## Building
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The DLL is built automatically as part of the Tauri build pipeline via `build-provisioner.mjs`:
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```bash
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cd frontend
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npm run tauri-build
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```
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To build the DLL standalone:
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```bash
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cd frontend/editor/src-tauri/thumbnail-handler
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cargo build --release
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# Output: target/release/stirling_thumbnail_handler.dll
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```
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## Linux / macOS
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This DLL is Windows-only. Linux and macOS don't need it — their thumbnail systems (thumbnailers on Linux, Quick Look on macOS) are decoupled from the default app association and continue working regardless of which app is set as default.
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