cad-editor/crates/dwg-thumbnailer

DWG thumbnails for OS file managers

dwg_thumbnailer::extract reads only the embedded preview from a DWG (file header → preview seeker → parse — never the whole drawing) and returns it as an image::RgbaImage. It's the shared core behind every platform's thumbnail integration.

crates/
  dwg-thumbnailer/        this crate — shared core + macOS extension sources
  dwg-thumbnailer-win/    Windows IThumbnailProvider COM DLL (depends on the core)

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Linux (COSMIC, GNOME, Nautilus, Nemo, …) — handled by OpenCADStudio itself

No separate binary. OpenCADStudio embeds this core and, on startup, installs a freedesktop .thumbnailer pointing at its own hidden --dwg-thumbnail mode (see src/io/file_association.rs::install_thumbnailer). Launch OCS once and file managers render DWG thumbnails; clear stale "no thumbnail" cache if needed:

rm -f ~/.cache/thumbnails/fail/*/*.png

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Windows (Explorer) — authored, build & test on Windows

A COM in-proc server implementing IThumbnailProvider. Not compiled/tested on the Linux dev host — build and verify on Windows.

cd crates\dwg-thumbnailer-win && cargo build --release
regsvr32 target\release\dwg_thumbnailer_win.dll        :: register (elevated)
regsvr32 /u target\release\dwg_thumbnailer_win.dll     :: unregister
ie4uinit.exe -show                                     :: refresh thumbnails

If regsvr32's self-registration needs adjusting, the equivalent registry keys are (replace the path):

Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\CLSID\{8F2A9C41-3B6E-4E2D-9C7A-1E0B5D6F42AA}]
@="OpenCADStudio DWG Thumbnail Provider"
[HKEY_CLASSES_ROOT\CLSID\{8F2A9C41-3B6E-4E2D-9C7A-1E0B5D6F42AA}\InprocServer32]
@="C:\\path\\to\\dwg_thumbnailer_win.dll"
"ThreadingModel"="Apartment"
[HKEY_CLASSES_ROOT\.dwg\ShellEx\{e357fccd-a995-4576-b01f-234630154e96}]
@="{8F2A9C41-3B6E-4E2D-9C7A-1E0B5D6F42AA}"

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macOS (Finder) — sources provided, build in Xcode

A QuickLook Thumbnail Extension (macos/ThumbnailProvider.swift) calls the Rust core's C ABI, linked as a static library. Requires Xcode + a host app.

1. Build the core as a static lib for your arch(s):

   cargo build -p dwg-thumbnailer --release --target aarch64-apple-darwin
   # → target/aarch64-apple-darwin/release/libdwg_thumbnailer.a
   

2. In Xcode, add a Thumbnail Extension target to a host app.
   • Use macos/Info.plist (lists the com.autodesk.dwg UTI).
   • Add macos/ThumbnailProvider.swift.
   • Add a bridging header that #includes macos/dwg_thumbnailer.h.
   • Link libdwg_thumbnailer.a (+ system frameworks it needs).
3. Sign, install the host app, and Finder picks up the extension.

C ABI (see dwg_thumbnailer.h): dwg_thumbnail_png(path, max_dim, &ptr, &len) / dwg_thumbnail_free(ptr, len).

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Formats: DWG BMP-DIB and PNG embedded previews decode. WMF previews and files without a preview (or DXF) produce no thumbnail — the file manager falls back.