1.used uvec2/ushort2 in AssignVBO

2.completed first step then merge MI buffer

inc/hgl/graph/MaterialRenderList.h

@@ -35,7 +35,7 @@ private:
         void Set(Renderable *);
     };
 
-    SortedSets<int> mi_id_set;
+    MaterialInstanceSets mi_set;
     DataArray<RenderItem> ri_array;
     uint ri_count;
 

inc/hgl/graph/RenderNode.h

@@ -22,6 +22,8 @@ namespace hgl
         };
 
         using RenderNodeList=List<RenderNode>;
+
+        using MaterialInstanceSets=SortedSets<MaterialInstance *>;       ///<材质实例集合
     }//namespace graph
 }//namespace hgl
 #endif//HGL_GRAPH_RENDER_NODE_INCLUDE