dsh-preview-stl

Preview STL meshes inside DeepSeek Harness: the right-Sidebar document preview renders the triangles in an interactive 3D viewport and reports the numbers that matter for 3D printing — size, volume, surface area and watertightness.

What it does

• Registers a document-preview renderer for .stl files, so clicking one in Workspace files opens it in the right Sidebar.
• Streams the file through an authenticated /api/preview/stl route and parses binary and ASCII STL in the browser — nothing is uploaded, nothing is converted on the host.
• Draws the mesh with the same dependency-free WebGL viewer used by dsh-preview-blender: orbit, pan, wheel zoom, double-click reset, wireframe, auto-rotate, contact shadow, axis triad. STL is Z-up, so the mesh is rotated into the Y-up viewport before drawing.
• Reports: format (binary/ASCII + header), file size, triangle count, welded vertex count, bounding box in millimetres, volume in cm³, surface area in cm², and watertightness (boundary edges / non-manifold edges / degenerate facets), computed by welding vertices on a grid and counting edge uses.
• Handles unitless STL with a configurable unitScale (1 = millimetres, 10 = centimetres, 25.4 = inches).

Requirements

• DeepSeek Harness 0.2.x (declared compatible with 0.2.0-rc.2 and 0.2.1-rc.2).
• A browser/GPU with WebGL (the desktop app always has it). No Blender, no slicer, no network.

Install

dsh plugin --profile <profile> add dsh-preview-stl

The desktop profile is owned by the Electron app; install there through the plugin manager UI, or compose it manually and restart. The package ships a cordis.patch.yml, so the plugin row is added automatically.

Configuration

Settings → Plugins → STL preview (namespace preview-stl):

Key	Default	Meaning
enabled	true	Register the renderer and the byte route.
routePath	/api/preview/stl	Authenticated mesh route. Must stay under /api; otherwise it falls back to the default.
extensions	["stl"]	Suffixes that open in the 3D preview.
maxBytes	536870912	Largest STL streamed (512 MiB).
chunkBytes	1048576	Bytes per ranged read on the host.
unitScale	1	Millimetres per STL unit; drives size, volume and area.
color	#c7d2e2	Viewport colour (STL carries no materials).
analysisMaxTriangles	400000	Above this, skip the watertightness pass instead of freezing the tab.

How it works

Workspace file click
        │
        ▼
document preview body (lib/client.js)
        │  GET /api/preview/stl?path=…   (raw bytes, ctx.fs chunks)
        ▼
parseStl(bytes)         binary: 80-byte header + uint32 count + 50 B/facet
                        ASCII:  facet normal / outer loop / vertex
        │
        ├── analyzeStl: bbox, area, signed volume, vertex weld + edge map
        └── setGeometry: rotate Z-up → Y-up, upload triangles

• The route sits under /api, so the connection service authenticates every request (Host/Origin fence + session cookie) before a byte is read.
• Watertightness is skipped above analysisMaxTriangles (the edge map is the expensive part); the panel says so.
• Volume is the signed tetrahedron sum (|Σ v0·(v1×v2)/6|), area the summed triangle areas.

Development

dev/client-body.js   client UI, STL parser and statistics (CJS factory)
dev/viewer.js        the WebGL renderer, spliced into the bundle at build time
scripts/build-client.mjs   builds lib/client.js from the two files
scripts/live-selftest.mjs  parses a real STL with the shipped bundle
scripts/e2e-browser.mjs    Playwright end-to-end against a temporary DSH host
node --test test/*.test.js

lib/client.js is generated — edit the files under dev/ and rebuild.

Notes and limits

• STL is unitless; the millimetre figures assume unitScale (1 by default). Set 10 for a file authored in centimetres.
• Very large meshes (millions of triangles) parse on the main thread and may take a moment; the watertightness pass stops at analysisMaxTriangles.
• ASCII STL with vertex colours or per-facet attributes beyond the standard grammar is not interpreted beyond positions and normals.
• Nothing is uploaded: bytes go browser ← host over the authenticated route and are parsed in the page.