added a cube builder

src/polymesh/objects.hh

 #pragma once
 
 // includes all supported objects
+#include "objects/cube.hh"
 #include "objects/quad.hh"

src/polymesh/objects/cube.hh

+#pragma once
+
+#include "../Mesh.hh"
+
+namespace polymesh
+{
+namespace objects
+{
+/// Adds a cube to the given mesh
+/// cf is called with (v, x, y, z), with vertex handle v and (x,y,z) from 0..1 (int literals)
+/// returns the one of the new vertices (usually the first)
+/// NOTE: the result is NOT triangulated!
+template <class CubeF>
+vertex_handle add_cube(Mesh& m, CubeF&& cf);
+
+/// ======== IMPLEMENTATION ========
+
+template <class CubeF>
+vertex_handle add_cube(Mesh& m, CubeF&& cf)
+{
+    auto v000 = m.vertices().add();
+    auto v001 = m.vertices().add();
+    auto v010 = m.vertices().add();
+    auto v011 = m.vertices().add();
+    auto v100 = m.vertices().add();
+    auto v101 = m.vertices().add();
+    auto v110 = m.vertices().add();
+    auto v111 = m.vertices().add();
+
+    m.faces().add(v000, v010, v110, v100);
+    m.faces().add(v000, v100, v101, v001);
+    m.faces().add(v000, v001, v011, v010);
+
+    m.faces().add(v001, v101, v111, v011);
+    m.faces().add(v010, v011, v111, v110);
+    m.faces().add(v100, v110, v111, v101);
+
+    cf(v000, 0, 0, 0);
+    cf(v001, 0, 0, 1);
+    cf(v010, 0, 1, 0);
+    cf(v011, 0, 1, 1);
+    cf(v100, 1, 0, 0);
+    cf(v101, 1, 0, 1);
+    cf(v110, 1, 1, 0);
+    cf(v111, 1, 1, 1);
+
+    return v000;
+}
+}
+}