added RenderNode class.

inc/hgl/graph/RenderNode.h

@@ -0,0 +1,25 @@
+#ifndef HGL_GRAPH_RENDER_NODE_INCLUDE
+#define HGL_GRAPH_RENDER_NODE_INCLUDE
+
+#include<hgl/math/Vector.h>
+#include<hgl/type/List.h>
+namespace hgl
+{
+    namespace graph
+    {
+        class RenderableInstance;
+
+        struct RenderNode
+        {
+            Vector4f WorldCenter;
+
+            float distance_to_camera_square;
+//            float distance_to_camera;
+
+            RenderableInstance *ri;
+        };//struct RenderNode
+
+        using RenderNodeList=List<RenderNode *>;
+    }//namespace graph
+}//namespace hgl
+#endif//HGL_GRAPH_RENDER_NODE_INCLUDE