Test implementation of phong shader

src/model/obj.h

@@ -33,6 +33,13 @@ struct phong_material {
   f32 shininess;
 };
 
+typedef struct directional_light DirectionalLight;
+struct directional_light {
+  V3f diffuse_intensity;
+  V3f specular_intensity;
+  V3f direction;
+};
+
 typedef struct model Model;
 struct model {
   LIST_TYPE(V3f) * vertices;