Add shallow copy semantics to Camera's, Object's, and Scene's.

14 files changed, 315 insertions, 125 deletions

diff --git a/libdimensionxx/camera.cpp b/libdimensionxx/camera.cpp
index 2897dac..ba2428a 100644
--- a/libdimensionxx/camera.cpp
+++ b/libdimensionxx/camera.cpp
@@ -22,37 +22,66 @@
 
 namespace Dimension
 {
-  // Pure virtual no-op destructor
+  // Virtual no-op destructor
   Camera::~Camera()
   { }
 
+  // Return the result of the dmnsn_camera*'s ray callback
+  Line
+  Camera::ray(const Canvas& canvas, unsigned int x, unsigned int y)
+  {
+    return Line(dmnsn()->ray_fn(dmnsn(), canvas.dmnsn(), x, y));
+  }
+
   // Return the wrapped camera
   dmnsn_camera*
   Camera::dmnsn()
   {
-    return m_camera;
+    if (!m_camera) {
+      throw Dimension_Error("Attempt to access NULL camera.");
+    }
+
+    return *m_camera;
   }
 
   // Return a const version of the wrapped canvas
   const dmnsn_camera*
   Camera::dmnsn() const
   {
-    return m_camera;
+    if (!m_camera) {
+      throw Dimension_Error("Attempt to access NULL camera.");
+    }
+
+    return *m_camera;
   }
 
   // Protected default no-op constructor
   Camera::Camera()
+    : m_camera()
+  { }
+
+  // Protected copy constructor
+  Camera::Camera(const Camera& camera)
+    : m_camera(camera.m_camera)
   { }
 
   // Protected manual constructor
   Camera::Camera(dmnsn_camera *camera)
-    : m_camera(camera)
+    : m_camera(new dmnsn_camera*(camera))
   { }
 
-  Line
-  Camera::ray(const Canvas& canvas, unsigned int x, unsigned int y)
+  // Is m_camera unique?
+  bool
+  Camera::unique() const
   {
-    return Line(m_camera->ray_fn(m_camera, canvas.dmnsn(), x, y));
+    return m_camera.unique();
+  }
+
+  // Set the wrapped dmnsn_camera*
+  void
+  Camera::dmnsn(dmnsn_camera* camera)
+  {
+    m_camera.reset(new dmnsn_camera*(camera));
   }
 
   // Custom camera callbacks
@@ -75,13 +104,15 @@ namespace Dimension
   Custom_Camera::Custom_Camera()
     : Camera(dmnsn_new_camera())
   {
-    m_camera->ptr = this;
-    m_camera->ray_fn = &ray_fn;
+    dmnsn()->ptr = this;
+    dmnsn()->ray_fn = &ray_fn;
   }
 
   // Delete the camera
   Custom_Camera::~Custom_Camera()
   {
-    dmnsn_delete_camera(m_camera);
+    if (unique()) {
+      dmnsn_delete_camera(dmnsn());
+    }
   }
 }
diff --git a/libdimensionxx/cameras.cpp b/libdimensionxx/cameras.cpp
index a7a8255..ea0bca9 100644
--- a/libdimensionxx/cameras.cpp
+++ b/libdimensionxx/cameras.cpp
@@ -26,7 +26,7 @@ namespace Dimension
   Perspective_Camera::Perspective_Camera(const Matrix& trans)
     : Camera(dmnsn_new_perspective_camera(trans.dmnsn()))
   {
-    if (!m_camera) {
+    if (!dmnsn()) {
       throw Dimension_Error("Failed to allocate perspective camera.");
     }
   }
@@ -34,18 +34,30 @@ namespace Dimension
   // Delete a perspective camera
   Perspective_Camera::~Perspective_Camera()
   {
-    dmnsn_delete_perspective_camera(m_camera);
+    if (unique()) {
+      dmnsn_delete_perspective_camera(dmnsn());
+    }
   }
 
   Matrix
   Perspective_Camera::trans()
   {
-    return Matrix(dmnsn_get_perspective_camera_trans(m_camera));
+    return Matrix(dmnsn_get_perspective_camera_trans(dmnsn()));
   }
 
   void
   Perspective_Camera::trans(const Matrix& trans)
   {
-    dmnsn_set_perspective_camera_trans(m_camera, trans.dmnsn());
+    dmnsn_set_perspective_camera_trans(dmnsn(), trans.dmnsn());
   }
+
+  Camera*
+  Perspective_Camera::copy() const
+  {
+    return new Perspective_Camera(*this);
+  }
+
+  Perspective_Camera::Perspective_Camera(const Perspective_Camera& camera)
+    : Camera(camera)
+  { }
 }
diff --git a/libdimensionxx/dimensionxx/camera.hpp b/libdimensionxx/dimensionxx/camera.hpp
index 950e16d..a883969 100644
--- a/libdimensionxx/dimensionxx/camera.hpp
+++ b/libdimensionxx/dimensionxx/camera.hpp
@@ -29,12 +29,15 @@ namespace Dimension
   class Camera
   {
   public:
-    // No-op, made pure virtual
-    virtual ~Camera() = 0;
+    // No-op
+    virtual ~Camera();
 
     // Camera callback
     virtual Line ray(const Canvas& canvas, unsigned int x, unsigned int y);
 
+    // Shallow-copy a derived camera
+    virtual Camera* copy() const = 0;
+
     // Access the wrapped C camera.
     dmnsn_camera*       dmnsn();
     const dmnsn_camera* dmnsn() const;
@@ -42,15 +45,22 @@ namespace Dimension
   protected:
     // No-op
     Camera();
+    // Shallow-copy
+    Camera(const Camera& camera);
     // Wrap an existing camera
     explicit Camera(dmnsn_camera* camera);
 
-    dmnsn_camera* m_camera;
+    // Is m_camera unique?
+    bool unique() const;
+
+    // Set the wrapped C camera
+    void dmnsn(dmnsn_camera* camera);
 
   private:
-    // Copying prohibited
-    Camera(const Camera&);
+    // Copy-assignment prohibited
     Camera& operator=(const Camera&);
+
+    std::tr1::shared_ptr<dmnsn_camera*> m_camera;
   };
 
   // A custom camera abstract base class, for creating your own camera types
diff --git a/libdimensionxx/dimensionxx/cameras.hpp b/libdimensionxx/dimensionxx/cameras.hpp
index 4e67d64..cabae97 100644
--- a/libdimensionxx/dimensionxx/cameras.hpp
+++ b/libdimensionxx/dimensionxx/cameras.hpp
@@ -30,10 +30,17 @@ namespace Dimension
   {
   public:
     Perspective_Camera(const Matrix& trans);
-    virtual ~Perspective_Camera();
+    ~Perspective_Camera();
 
     Matrix trans();
     void trans(const Matrix& trans);
+
+    Camera* copy() const;
+
+  private:
+    // Copying prohibited, but used internally
+    Perspective_Camera(const Perspective_Camera& camera);
+    Perspective_Camera& operator=(const Perspective_Camera&);
   };
 }
 
diff --git a/libdimensionxx/dimensionxx/object.hpp b/libdimensionxx/dimensionxx/object.hpp
index 1b9c848..c56d358 100644
--- a/libdimensionxx/dimensionxx/object.hpp
+++ b/libdimensionxx/dimensionxx/object.hpp
@@ -29,8 +29,8 @@ namespace Dimension
   class Object
   {
   public:
-    // No-op, made pure virtual
-    virtual ~Object() = 0;
+    // No-op
+    virtual ~Object();
 
     // Get/set the transformation matrix
     Matrix trans();
@@ -40,6 +40,9 @@ namespace Dimension
     virtual Array<double> intersections(const Line& l);
     virtual bool inside(const Vector& point);
 
+    // Shallow-copy a derived
+    virtual Object* copy() const = 0;
+
     // Access the wrapped C object.
     dmnsn_object*       dmnsn();
     const dmnsn_object* dmnsn() const;
@@ -47,15 +50,22 @@ namespace Dimension
   protected:
     // No-op
     Object();
+    // Shallow copy
+    Object(const Object& object);
     // Wrap an existing object.
     explicit Object(dmnsn_object* object);
 
-    dmnsn_object* m_object;
+    // Is m_object unique?
+    bool unique() const;
+
+    // Set the wrapped object
+    void dmnsn(dmnsn_object* object);
 
   private:
-    // Copying prohibited
-    Object(const Object&);
+    // Copy-assignment prohibited
     Object& operator=(const Object&);
+
+    std::tr1::shared_ptr<dmnsn_object*> m_object;
   };
 
   // A custom object abstract base class, for creating your own object types
diff --git a/libdimensionxx/dimensionxx/objects.hpp b/libdimensionxx/dimensionxx/objects.hpp
index 89aab14..5b43dc4 100644
--- a/libdimensionxx/dimensionxx/objects.hpp
+++ b/libdimensionxx/dimensionxx/objects.hpp
@@ -30,7 +30,14 @@ namespace Dimension
   {
   public:
     Sphere();
-    virtual ~Sphere();
+    ~Sphere();
+
+    Object* copy() const;
+
+  private:
+    // Copying prohibited, but used internally
+    Sphere(const Sphere& sphere);
+    Sphere& operator=(const Sphere&);
   };
 
   // A cube
@@ -38,7 +45,14 @@ namespace Dimension
   {
   public:
     Cube();
-    virtual ~Cube();
+    ~Cube();
+
+    Object* copy() const;
+
+  private:
+    // Copying prohibited, but used internally
+    Cube(const Cube& cube);
+    Cube& operator=(const Cube&);
   };
 }
 
diff --git a/libdimensionxx/dimensionxx/scene.hpp b/libdimensionxx/dimensionxx/scene.hpp
index 256de29..b5adde0 100644
--- a/libdimensionxx/dimensionxx/scene.hpp
+++ b/libdimensionxx/dimensionxx/scene.hpp
@@ -25,14 +25,20 @@
 
 namespace Dimension
 {
+  // Iterator class for scene objects
+  class Scene_Iterator;
+
   // Base scene class.  Wraps a dmnsn_scene*.
   class Scene
   {
   public:
-    // Allocate a dmnsn_scene
+    typedef Scene_Iterator Iterator;
+
+    // Allocate a dmnsn_scene*
     Scene(const Color& background, Camera& camera, Canvas& canvas);
-    // Wrap an existing scene
-    explicit Scene(dmnsn_scene* scene);
+
+    // Scene(const Scene& scene);
+
     // Delete the scene
     ~Scene();
 
@@ -43,7 +49,11 @@ namespace Dimension
     Canvas&       canvas();
     const Canvas& canvas() const;
 
-    // Add objects
+    // Object access
+
+    Iterator begin();
+    Iterator end();
+
     void push_object(Object& object);
 
     // Access the wrapped C object.
@@ -51,13 +61,38 @@ namespace Dimension
     const dmnsn_scene* dmnsn() const;
 
   private:
-    // Copying prohibited
-    Scene(const Scene&);
+    // Copy-assignment prohibited
     Scene& operator=(const Scene&);
 
-    dmnsn_scene* m_scene;
-    Camera* m_camera;
-    Canvas* m_canvas;
+    std::tr1::shared_ptr<dmnsn_scene*> m_scene;
+    std::tr1::shared_ptr<Camera> m_camera;
+    std::tr1::shared_ptr<Canvas> m_canvas;
+    std::list<std::tr1::shared_ptr<Object> > m_objects;
+  };
+
+  class Scene_Iterator
+  {
+  public:
+    Scene_Iterator(std::list<std::tr1::shared_ptr<Object> >::iterator i)
+      : m_i(i) { }
+    // Scene_Iterator(const Scene_Iterator& i);
+    // ~Scene_Iterator();
+
+    // Scene_Iterator& operator=(const Scene_Iterator& i);
+
+    Object& operator*() const { return **m_i; }
+    Object* operator->() const { return &**m_i; }
+
+    bool operator==(Scene_Iterator i) const { return m_i == i.m_i; }
+    bool operator!=(Scene_Iterator i) const { return m_i != i.m_i; }
+
+    Scene_Iterator& operator++()    { ++m_i; return *this; }
+    Scene_Iterator  operator++(int) { return Scene_Iterator(m_i++); }
+    Scene_Iterator& operator--()    { --m_i; return *this; }
+    Scene_Iterator  operator--(int) { return Scene_Iterator(m_i--); }
+
+  private:
+    std::list<std::tr1::shared_ptr<Object> >::iterator m_i;
   };
 }
 
diff --git a/libdimensionxx/object.cpp b/libdimensionxx/object.cpp
index 7d66206..61b8b7d 100644
--- a/libdimensionxx/object.cpp
+++ b/libdimensionxx/object.cpp
@@ -22,59 +22,87 @@
 
 namespace Dimension
 {
-  // Pure virtual no-op destructor
+  // Virtual no-op destructor
   Object::~Object()
   { }
 
   Matrix
   Object::trans()
   {
-    return Matrix(m_object->trans);
+    return Matrix(dmnsn()->trans);
   }
 
   void
   Object::trans(const Matrix& trans)
   {
-    m_object->trans = trans.dmnsn();
+    dmnsn()->trans = trans.dmnsn();
   }
 
   // Intersection list for the line l
   Array<double>
   Object::intersections(const Line& l)
   {
-    return Array<double>(m_object->intersections_fn(m_object, l.dmnsn()));
+    return Array<double>(dmnsn()->intersections_fn(dmnsn(), l.dmnsn()));
   }
 
   // Whether the point `point' is inside the object
   bool
   Object::inside(const Vector& point)
   {
-    return m_object->inside_fn(m_object, point.dmnsn());
+    return dmnsn()->inside_fn(dmnsn(), point.dmnsn());
   }
 
   // Return the wrapped object
   dmnsn_object*
   Object::dmnsn()
   {
-    return m_object;
+    if (!m_object) {
+      throw Dimension_Error("Attempt to access NULL object.");
+    }
+
+    return *m_object;
   }
 
   // Return a const version of the wrapped canvas
   const dmnsn_object*
   Object::dmnsn() const
   {
-    return m_object;
+    if (!m_object) {
+      throw Dimension_Error("Attempt to access NULL object.");
+    }
+
+    return *m_object;
   }
 
   // Protected default no-op constructor
   Object::Object()
+    : m_object()
+  { }
+
+  // Protected copy constructor
+  Object::Object(const Object& object)
+    : m_object(object.m_object)
   { }
 
   // Protected manual constructor
-  Object::Object(dmnsn_object *object)
-    : m_object(object)
+  Object::Object(dmnsn_object* object)
+    : m_object(new dmnsn_object*(object))
   { }
 
+  // Is m_object unique?
+  bool
+  Object::unique() const
+  {
+    return m_object.unique();
+  }
+
+  // Set the wrapped dmnsn_object*
+  void
+  Object::dmnsn(dmnsn_object* object)
+  {
+    m_object.reset(new dmnsn_object*(object));
+  }
+
   // Custom object callbacks
   namespace {
     dmnsn_array *
@@ -96,14 +124,16 @@ namespace Dimension
   Custom_Object::Custom_Object()
     : Object(dmnsn_new_object())
   {
-    m_object->ptr = this;
-    m_object->intersections_fn = &intersections_fn;
-    m_object->inside_fn = &inside_fn;
+    dmnsn()->ptr = this;
+    dmnsn()->intersections_fn = &intersections_fn;
+    dmnsn()->inside_fn = &inside_fn;
   }
 
   // Delete the object
   Custom_Object::~Custom_Object()
   {
-    dmnsn_delete_object(m_object);
+    if (unique()) {
+      dmnsn_delete_object(dmnsn());
+    }
   }
 }
diff --git a/libdimensionxx/objects.cpp b/libdimensionxx/objects.cpp
index 1b78731..eac642c 100644
--- a/libdimensionxx/objects.cpp
+++ b/libdimensionxx/objects.cpp
@@ -26,7 +26,7 @@ namespace Dimension
   Sphere::Sphere()
     : Object(dmnsn_new_sphere())
   {
-    if (!m_object) {
+    if (!dmnsn()) {
       throw Dimension_Error("Failed to allocate sphere.");
     }
   }
@@ -34,14 +34,28 @@ namespace Dimension
   // Delete a sphere
   Sphere::~Sphere()
   {
-    dmnsn_delete_sphere(m_object);
+    if (unique()) {
+      dmnsn_delete_sphere(dmnsn());
+    }
   }
 
+  // Shallow copy a sphere
+  Object*
+  Sphere::copy() const
+  {
+    return new Sphere(*this);
+  }
+
+  // Protected copy constructor
+  Sphere::Sphere(const Sphere& sphere)
+    : Object(sphere)
+  { }
+
   // Create a cube
   Cube::Cube()
     : Object(dmnsn_new_cube())
   {
-    if (!m_object) {
+    if (!dmnsn()) {
       throw Dimension_Error("Failed to allocate cube.");
     }
   }
@@ -49,6 +63,20 @@ namespace Dimension
   // Delete a sphere
   Cube::~Cube()
   {
-    dmnsn_delete_cube(m_object);
+    if (unique()) {
+      dmnsn_delete_cube(dmnsn());
+    }
   }
+
+  // Shallow copy a cube
+  Object*
+  Cube::copy() const
+  {
+    return new Cube(*this);
+  }
+
+  // Protected copy constructor
+  Cube::Cube(const Cube& sphere)
+    : Object(sphere)
+  { }
 }
diff --git a/libdimensionxx/scene.cpp b/libdimensionxx/scene.cpp
index f5e4ea8..2b0fba5 100644
--- a/libdimensionxx/scene.cpp
+++ b/libdimensionxx/scene.cpp
@@ -24,25 +24,24 @@ namespace Dimension
 {
   // Allocate a dmnsn_scene
   Scene::Scene(const Color& background, Camera& camera, Canvas& canvas)
-    : m_scene(dmnsn_new_scene()), m_camera(&camera), m_canvas(&canvas)
+    : m_scene(new dmnsn_scene*(dmnsn_new_scene())), m_camera(camera.copy()),
+      m_canvas(new Canvas(canvas))
   {
     if (!m_scene) {
       throw Dimension_Error("Couldn't allocate scene.");
     }
 
-    m_scene->background = background.dmnsn();
-    m_scene->camera = camera.dmnsn();
-    m_scene->canvas = canvas.dmnsn();
+    dmnsn()->background = background.dmnsn();
+    dmnsn()->camera = this->camera().dmnsn();
+    dmnsn()->canvas = this->canvas().dmnsn();
   }
 
-  // Wrap an existing scene
-  Scene::Scene(dmnsn_scene* scene)
-    : m_scene(scene) { }
-
   // Delete the scene
   Scene::~Scene()
   {
-    dmnsn_delete_scene(m_scene);
+    if (m_scene.unique()) {
+      dmnsn_delete_scene(dmnsn());
+    }
   }
 
   // Element access
@@ -50,7 +49,7 @@ namespace Dimension
   Color
   Scene::background() const
   {
-    return Color(m_scene->background);
+    return Color(dmnsn()->background);
   }
 
   Camera&
@@ -77,12 +76,27 @@ namespace Dimension
     return *m_canvas;
   }
 
-  // Add objects
+  // An iterator to the beginning of the object list
+  Scene::Iterator
+  Scene::begin()
+  {
+    return Iterator(m_objects.begin());
+  }
+
+  // An iterator one past the end of the object list
+  Scene::Iterator
+  Scene::end()
+  {
+    return Iterator(m_objects.end());
+  }
+
+  // Add an object
   void
   Scene::push_object(Object& object)
   {
+    m_objects.push_back(std::tr1::shared_ptr<Object>(object.copy()));
     dmnsn_object* cobject = object.dmnsn();
-    dmnsn_array_push(m_scene->objects, &cobject);
+    dmnsn_array_push(dmnsn()->objects, &cobject);
   }
 
   // Access the wrapped C object.
@@ -90,12 +104,12 @@ namespace Dimension
   dmnsn_scene*
   Scene::dmnsn()
   {
-    return m_scene;
+    return *m_scene;
   }
 
   const dmnsn_scene*
   Scene::dmnsn() const
   {
-    return m_scene;
+    return *m_scene;
   }
 }
diff --git a/tests/glxx.cpp b/tests/glxx.cpp
index eb74209..aaf7b7b 100644
--- a/tests/glxx.cpp
+++ b/tests/glxx.cpp
@@ -26,37 +26,24 @@ int
 main() {
   using namespace Dimension;
 
-  // Set the resilience low for tests
-  resilience(SEVERITY_LOW);
-
-  // Background color
-  Color background = sRGB(0.0, 0.1, 0.25);
-  background.filter(0.1);
-
-  // Canvas
-  Canvas canvas(768, 480);
-
-  // Camera
-  Perspective_Camera camera(
-    Matrix::rotation(Vector(0.0, 1.0, 0.0))
-    * Matrix::translation(Vector(0.0, 0.0, -4.0))
-    * Matrix::scale(
-        Vector(static_cast<double>(canvas.width())/canvas.height(), 1.0, 1.0)
-      )
-  );
+  Scene scene = default_scene();
 
-  // Scene
-  Scene scene(background, camera, canvas);
+  Perspective_Camera& camera
+    = dynamic_cast<Perspective_Camera&>(scene.camera());
 
-  // Objects in scene
-
-  Sphere sphere;
-  sphere.trans(inverse(Matrix::scale(Vector(1.25, 1.25, 1.25))));
-  scene.push_object(sphere);
+  Cube* cube;
+  for (Scene::Iterator i = scene.begin(); i != scene.end(); ++i) {
+    cube = dynamic_cast<Cube*>(&*i);
+    if (cube) {
+      break;
+    }
+  }
+  if (!cube) {
+    throw Dimension_Error("Couldn't find a cube in the default scene.");
+  }
 
-  Cube cube;
-  cube.trans(inverse(Matrix::rotation(Vector(0.75, 0.0, 0.0))));
-  scene.push_object(cube);
+  // Set the resilience low for tests
+  resilience(SEVERITY_LOW);
 
   Raytracer raytracer(scene);
   GL_Drawer drawer(scene.canvas());
@@ -71,7 +58,7 @@ main() {
     drawer.draw();
     display.flush();
 
-    cube.trans(inverse(Matrix::rotation(Vector(0.025, 0.0, 0.0)))*cube.trans());
+    cube->trans(inverse(Matrix::rotation(Vector(0.025, 0.0, 0.0)))*cube->trans());
     camera.trans(Matrix::rotation(Vector(0.0, -0.05, 0.0))*camera.trans());
   }
 
diff --git a/tests/raytracexx.cpp b/tests/raytracexx.cpp
index c04e525..4202347 100644
--- a/tests/raytracexx.cpp
+++ b/tests/raytracexx.cpp
@@ -28,34 +28,7 @@ main() {
   // Set the resilience low for tests
   resilience(SEVERITY_LOW);
 
-  // Background color
-  Color background = sRGB(0.0, 0.1, 0.25);
-  background.filter(0.1);
-
-  // Canvas
-  Canvas canvas(768, 480);
-
-  // Camera
-  Perspective_Camera camera(
-    Matrix::rotation(Vector(0.0, 1.0, 0.0))
-    * Matrix::translation(Vector(0.0, 0.0, -4.0))
-    * Matrix::scale(
-        Vector(static_cast<double>(canvas.width())/canvas.height(), 1.0, 1.0)
-      )
-  );
-
-  // Scene
-  Scene scene(background, camera, canvas);
-
-  // Objects in scene
-
-  Sphere sphere;
-  sphere.trans(inverse(Matrix::scale(Vector(1.25, 1.25, 1.25))));
-  scene.push_object(sphere);
-
-  Cube cube;
-  cube.trans(inverse(Matrix::rotation(Vector(0.75, 0.0, 0.0))));
-  scene.push_object(cube);
+  Scene scene = default_scene();
 
   // Render the scene
   {
@@ -66,7 +39,7 @@ main() {
 
   // Write the canvas
   std::ofstream file("raytracexx.png");
-  PNG_Writer writer(canvas, file);
+  PNG_Writer writer(scene.canvas(), file);
   Progress progress = writer.write_async();
   std::cout << "Writing PNG file: " << progress << std::endl;
 
diff --git a/tests/testsxx.cpp b/tests/testsxx.cpp
index f3dcca5..399e50f 100644
--- a/tests/testsxx.cpp
+++ b/tests/testsxx.cpp
@@ -21,6 +21,41 @@
 
 namespace Dimension
 {
+  Scene
+  default_scene()
+  {
+    // Background color
+    Color background = sRGB(0.0, 0.1, 0.25);
+    background.filter(0.1);
+
+    // Canvas
+    Canvas canvas(768, 480);
+
+    // Camera
+    Perspective_Camera camera(
+      Matrix::rotation(Vector(0.0, 1.0, 0.0))
+      * Matrix::translation(Vector(0.0, 0.0, -4.0))
+      * Matrix::scale(
+          Vector(static_cast<double>(canvas.width())/canvas.height(), 1.0, 1.0)
+        )
+    );
+
+    // Scene
+    Scene scene(background, camera, canvas);
+
+    // Objects in scene
+
+    Sphere sphere;
+    sphere.trans(inverse(Matrix::scale(Vector(1.25, 1.25, 1.25))));
+    scene.push_object(sphere);
+
+    Cube cube;
+    cube.trans(inverse(Matrix::rotation(Vector(0.75, 0.0, 0.0))));
+    scene.push_object(cube);
+
+    return scene;
+  }
+
   Display::Display(const Canvas& canvas)
     : m_display(dmnsn_new_display(canvas.dmnsn()))
   {
diff --git a/tests/testsxx.hpp b/tests/testsxx.hpp
index 0e522ad..1101196 100644
--- a/tests/testsxx.hpp
+++ b/tests/testsxx.hpp
@@ -26,6 +26,10 @@
 
 namespace Dimension
 {
+  // Helper to return a basic scene
+  Scene default_scene();
+
+  // Display abstraction
   class Display
   {
   public: