Build pipeline

How a Go source file in cmd/ becomes a printable STL, a coloured 3MF, and a set of dimensioned SVG cutaways.

go3dp build pipeline

Stages

  1. Source — each part lives in its own cmd/<part>/ directory as a small main package. Geometry is defined in plain Go using gsdf primitives plus the shared pkg/fasteners catalogue (WoodScrew schematic / threaded / wall-cutout variants). main.go parses flags (-size, -part, -out, -mesh) and dispatches to the build pipeline below.
  2. SDF tree — gsdf composes primitives (boxes, cylinders, octagonal prisms, screws, etc.) with boolean operations into a single signed-distance-function tree. No mesh yet — just a function that, given a 3D point, returns the signed distance to the surface.
  3. CPU evaluation — gleval.NewCPUSDF3 compiles the tree for fast batched evaluation on the CPU. The same evaluator drives both the mesh renderers (3D grid sampling) and the SVG slicer (2D plane sampling).
  4. Mesh rendering — two algorithms, picked by the -mesh flag:
    • OctreeRenderer (marching cubes) — original pipeline, larger triangle counts, tolerant of slicer quirks.
    • DualContourRenderer (dual contouring) — sharper edges on flat faces, fewer triangles before merging.
  5. Optional planar merge — pkg/meshopt.PlanarMerge collapses fans of coplanar triangles back to single polygons (re-triangulated as fans). Default for 3MF; cuts adaptor file size by ~95%, and blocks/covers by 15-35%. Skipped for -mesh=octree and -mesh=dc.
  6. Cross-section slicing — pkg/svgslice evaluates the SDF on a user-supplied plane (origin + U/V basis vectors), runs marching squares to extract contour line segments, and writes them as an SVG <path> with optional dimension annotations and labels.
  7. Writers:
    • STL — gsdfaux.RenderShader3D → binary STL via glrender.NewOctreeRenderer.
    • 3MF — gsdf-3mf zips a 3D Manufacturing Format file with one part per colour. Used for browser previews and for slicers that respect material assignments.
    • SVG — svgslice.WriteSliceLabelled writes a millimetre-scale SVG, suitable both for documentation and for round-tripping into 2D CAD.

Mesher choice

The -mesh flag for 3MF output trades file size against pipeline complexity. The task v0:3mf shortcut uses the default (merge).

-mesh Triangles When to use
merge Smallest Default. Coplanar fans collapsed. Adaptors shrink ~95%.
dc Medium Same triangle count as merge before the merge step — useful to bisect a slicer issue blamed on the merge pass.
octree Largest Original pipeline. Use if a slicer rejects the merged output (potential T-junctions across faces).

Where each artefact comes from

Artefact Pipeline
*.stl gsdf → gleval → octree → WriteBinarySTL
*.3mf (default) gsdf → gleval → dual contouring → planar merge → gsdf-3mf
*.3mf (-mesh=dc) gsdf → gleval → dual contouring → gsdf-3mf
*.3mf (-mesh=octree) gsdf → gleval → octree → gsdf-3mf
*_cutaway_*.svg gsdf → gleval → svgslice (marching squares + labels)

Source