Refactor|Renderer|Sky: Introduced an animator abstraction for the sky

Began splitting up the renderer's Sky class into subcomponents. The
first of which will be an animator for separation of these duties from
the GL drawable/rendering logic.

doomsday/client/include/render/sky.h

@@ -22,13 +22,14 @@
 #define DENG_CLIENT_RENDER_SKY_H
 
 #include "Material"
+#include <QFlags>
 #include <de/libcore.h>
 #include <de/Error>
 #include <de/Observers>
 #include <de/Vector>
 #include <doomsday/defs/ded.h>
 #include <doomsday/defs/sky.h>
-#include <QFlags>
+#include "ModelDef"
 
 #define MAX_SKY_LAYERS                   ( 2 )
 #define MAX_SKY_MODELS                   ( 32 )
@@ -46,9 +47,15 @@
 class Sky
 {
 public:
+    /// No animator is presently configured. @ingroup errors
+    DENG2_ERROR(MissingAnimatorError);
+
     /// Required layer is missing. @ingroup errors
     DENG2_ERROR(MissingLayerError);
 
+    /// Required model is missing. @ingroup errors
+    DENG2_ERROR(MissingModelError);
+
     /**
      * Multiple layers can be used for parallax effects.
      */
@@ -156,6 +163,48 @@ class Sky
         float _fadeoutLimit;
     };
 
+    struct ModelInfo
+    {
+        de::Record const *def; // Sky model def
+        ModelDef *model;
+        int frame;
+        int timer;
+        int maxTimer;
+        float yaw;
+    };
+
+    /**
+     * Sky sphere and model animator.
+     *
+     * Animates a sky according to the configured definition.
+     */
+    class Animator
+    {
+    public:
+        Animator();
+        Animator(Sky &sky);
+        virtual ~Animator();
+
+        void setSky(Sky &sky);
+        Sky &sky() const;
+
+        /**
+         * Reconfigure according to the specified @a definition if not @c NULL,
+         * otherwise, reconfigure using the default values.
+         */
+        void configure(defn::Sky *definition);
+
+        /**
+         * Advances the animation state.
+         *
+         * @param elapsed  Duration of elapsed time.
+         */
+        void advanceTime(timespan_t elapsed);
+
+    public:
+        DENG2_PRIVATE(d)
+    };
+
 public:
     Sky();
 
@@ -164,16 +213,14 @@ class Sky
      */
     void configureDefault();
 
-    /**
-     * Reconfigure the sky according the specified @a definition if not @c NULL,
-     * otherwise, setup using suitable defaults.
-     */
-    void configure(defn::Sky *sky);
+    bool hasAnimator() const;
+    void setAnimator(Animator *newAnimator);
+    Animator &animator();
 
     /**
-     * Animate the sky.
+     * Models are set up according to the given @a skyDef.
      */
-    void runTick();
+    void setupModels(defn::Sky const &skyDef);
 
 #ifdef __CLIENT__
 
@@ -220,6 +267,30 @@ class Sky
      */
     int firstActiveLayer() const;
 
+    /**
+     * Determines whether the specified sky model @a index is valid.
+     *
+     * @see model(), modelPtr()
+     */
+    bool hasModel(int index) const;
+
+    /**
+     * Lookup a sky model by it's unique @a index.
+     *
+     * @see hasModel()
+     */
+    ModelInfo &model(int index);
+
+    /// @copydoc model()
+    ModelInfo const &model(int index) const;
+
+    /**
+     * Returns a pointer to the referenced sky model; otherwise @c 0.
+     *
+     * @see hasModel(), model()
+     */
+    inline ModelInfo *modelPtr(int index) { return hasModel(index)? &model(index) : 0; }
+
     /**
      * Returns the horizon offset for the sky.
      *