Module thumbnail 

Preview images that CAD programs store inside their own files – the thumbnails Autodesk Vault or Teamcenter show for native files (findings in docs/src/research/cad-previews.md). Only the image is read, never the geometry:

• Autodesk Inventor (.ipt, .iam, .idw, .ipn) and Siemens Solid Edge (.par, .psm, .asm, .pwd, .dft) files are OLE compound files (MS-CFB); the preview is a PNG or a Windows DIB in one of their streams, normally the thumbnail property of the summary information (MS-OLEPS);
• SolidWorks files up to 2014 are OLE files as well (PreviewPNG), newer ones keep the PNG in a Deflate-compressed PreviewPNG section of their own container (swpart);
• NX parts keep a JPEG in their stream container (nxpart). It is small and poor, so NX parts get a thumbnail rendered from their 3D preview instead (rendered, render_mesh); the JPEG stays the fallback for NX files without one (assemblies, drawings).

Every candidate is validated (PNG chunk structure and checksums, plausible DIB header and sizes); the summary information wins, then streams named like a preview, then the largest image. A DIB is served as BMP, which all browsers and web views display. The layouts follow the documented containers and open-source readers (e.g. cad-preview); they were not tested with real files of every CAD program version.

Structs

Thumbnail

An image found in a file.

Constants

CACHE_VERSION

Bump to invalidate every cached thumbnail (2: SOLIDWORKS 2015+ previews, cached as “none” before; 3: NX parts rendered from their 3D preview instead of the embedded JPEG; 4: SOLIDWORKS parts and assemblies rendered from their 3D preview; 5: Rhino models; 6: Inventor parts and assemblies rendered from their 3D preview; 7: Inventor files with Zstandard segments, which kept their stored image before, #271; 8: Creo parts rendered from their 3D preview – both branches had used 7; 9: Creo assemblies rendered from their parts, turned Creo parts without a plane in the identity frame).

RENDERED_SIZE

Side of the thumbnails rendered from a 3D preview.

Functions

cached

The thumbnail of a vault blob, cached next to the 3D previews (previews/ab/<sha256>.thumb.v<N>.png|bmp|jpg|none).

extract

The preview image of a CAD file, if it has one.

extract_from

extract for any seekable reader (the fuzz targets pass bytes).

lookup

A thumbnail already in the cache: Some(None) when the blob is known to have none, None when it was never looked at.

render_mesh

A PNG thumbnail drawn from a cached preview mesh (TCMESH01).

rendered

Formats whose thumbnail is rendered from their 3D preview instead of the image stored in the file: NX parts (the embedded JPEG is small and poor, the tessellation in the file is good), SOLIDWORKS and Inventor parts and assemblies, Rhino and SketchUp models, CATIA V5 parts and products, Creo parts, Fusion designs (one look for every CAD system) and stand-alone JT files (a visualisation format: the tessellation is the content). Files without a 3D preview (drawings, assemblies none of whose parts are in TeamCraft, Rhino models saved without meshes, SketchUp files without faces, Fusion files without a display scene) keep the stored image.

store

Stores a thumbnail (rendered or found in the file) in the cache.

supports

Formats whose files carry a preview image.