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cad-editor/crates/dwg-thumbnailer/README.md
Hakan Seven ba3b3202e8 feat(thumbnails): embed DWG previews and wire cross-platform file thumbnails 
Round-trip a raster preview through the DWG's embedded preview slot and
surface it to the OS file managers, so drawings show their contents in
Explorer / Finder / Nautilus instead of a generic document icon.

OCS:
* io::thumbnail — rasterize the scene to a BMP DIB on save (embedded via
  acadrust's new Preview type) and read it back on open for the Start
  page recent list; `--dwg-thumbnail IN OUT SIZE` CLI extracts a badged
  PNG for external thumbnailers.
* io::file_association::install_thumbnailer — self-install the OS
  integration on startup: Linux writes a .thumbnailer + hicolor mimetype
  icons; Windows registers the IThumbnailProvider DLL under HKCU.

Shared core:
* crates/dwg-thumbnailer — lean (image-only) preview extractor + the
  `badge_dwg` full-width "DWG" band, used by every platform so the
  ribbon is single-sourced. Ships an rlib+staticlib.
* crates/dwg-thumbnailer-win — IThumbnailProvider COM in-proc server
  (cfg(windows), CI-built as a workspace member).
* macos/ — QuickLook thumbnail extension (Swift + C-ABI bridge to the
  core staticlib), assembled into a .appex.

Icons & packaging (single SVG source -> per-platform assets in CI):
* assets/mimetypes/image-vnd.{dwg,dxf}.svg — themed file icons.
* packaging: WiX ships dwg/dxf.ico + the thumbnail DLL and points the
  ProgIds at them; Info.plist gets CFBundleTypeIconFile + the QuickLook
  extension in Contents/PlugIns.
* release.yml — generate .ico (Windows) and .icns (macOS) from the SVGs,
  build the QuickLook .appex, and bundle everything.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-07-11 01:27:17 +03:00

3 KiB
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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)

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

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}"

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).

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.