blender: add tentative triangle support

blender.py

@@ -46,12 +46,14 @@ def render_polygons(f, name, polygons):
     uv_ix = 0
     for i, polygon in enumerate(polygons):
         indices = [*polygon.vertices, polygon.material_index, uv_ix]
+        if len(polygon.vertices) == 3:
+            indices = [*polygon.vertices, -1, polygon.material_index, uv_ix]
         uv_ix += len(polygon.vertices)
         s = ", ".join(map(str, indices))
-        if len(polygon.vertices) == 4:
+        if len(polygon.vertices) in {3, 4}:
             f.write(f"  {{{s}}},\n")
         else:
-            f.write(f"  {{0, 0, 0, 0, -1}}, // {{{s}}}\n")
+            f.write(f"  {{-1, -1, -1, -1, -1, -1}}, // {{{s}}}\n")
     f.write("};\n\n")
 
 def render_polygon_edge_pairs(f, name, polygons):

math/transform.hpp

@@ -22,6 +22,17 @@ inline constexpr mat<4, 4, T> scale(vec<3, T> s)
   };
 }
 
+template <typename T>
+inline constexpr mat<4, 4, T> scale(T s)
+{
+  return {
+      s,   0,   0, 0,
+      0,   s,   0, 0,
+      0,   0,   s, 0,
+      0,   0,   0, 1
+  };
+}
+
 template <typename T>
 inline constexpr mat<4, 4, T> rotate_x(T t)
 {