This vex is in the right direction, but it ends up with 6 vertices where I'd like 4 (one vertex per point).
int pts[]; push(pts, addpoint(0,{0,0,0})); push(pts, addpoint(0,{0,1,0})); push(pts, addpoint(0,{0,1,1})); push(pts, addpoint(0,{0,0,1})); void AddTriangulatedQuad(int pt0, pt1, pt2, pt3){ int triangle0 = addprim(0,'poly'); addvertex(0, triangle0, pt0); addvertex(0, triangle0, pt1); addvertex(0, triangle0, pt2); int triangle1 = addprim(0,'poly'); addvertex(0, triangle1, pt0); addvertex(0, triangle1, pt2); addvertex(0, triangle1, pt3); } AddTriangulatedQuad(pts[0], pts[1], pts[2], pts[3]);