Polygon extrusion

The minimum useful OCCT example: a four-point polygon extruded along Z.

import type { TopoDS_Shape } from '@taucad/opencascade.js';
import { getOc } from './ocjs-init';

export const buildExtrudedPolygon = async (): Promise<TopoDS_Shape> => {
  const oc = await getOc();

  using polygon = new oc.BRepBuilderAPI_MakePolygon();
  polygon.Add(new oc.gp_Pnt(-50, -50, 0));
  polygon.Add(new oc.gp_Pnt(50, -50, 0));
  polygon.Add(new oc.gp_Pnt(50, 50, 0));
  polygon.Add(new oc.gp_Pnt(-50, 50, 0));
  polygon.Close();

  using face = new oc.BRepBuilderAPI_MakeFace(polygon.Wire(), false);
  using prismVec = new oc.gp_Vec(0, 0, 40);
  using prism = new oc.BRepPrimAPI_MakePrism(face.Face(), prismVec, false, true);
  return prism.Shape();
};

Why this matters

• BRepBuilderAPI_MakePolygon accepts an arbitrary number of points — three for a triangle, hundreds for a complex contour.
• Close() adds the implicit closing edge.
• BRepBuilderAPI_MakeFace(wire, false) faces the wire; false means "this is the only wire of the face" (set true if you're adding holes later).
• BRepPrimAPI_MakePrism extrudes along an arbitrary direction vector, not just Z.

Swap gp_Vec(0, 0, 40) for gp_Vec(0.5, 0.5, 1) and you get a slanted prism. Swap the polygon for a BRepBuilderAPI_MakeWire with curved edges and you get an extruded curved profile.

Next steps

• Combine multiple extrusions with BRepAlgoAPI_Fuse for additive construction.
• Subtract holes with BRepAlgoAPI_Cut.
• Fillet sharp edges with BRepFilletAPI_MakeFillet.

See First shape tutorial for the fillet pattern.