Follow-up of d54548367a -> Reintroduce GLCanvas3D::m_old_size to avoid unneeded calls to render()

src/slic3r/GUI/GLCanvas3D.hpp

@@ -425,6 +425,10 @@ private:
     Model* m_model;
     BackgroundSlicingProcess *m_process;
 
+#if ENABLE_SCROLLABLE_LEGEND
+    std::array<unsigned int, 2> m_old_size{ 0, 0 };
+#endif // ENABLE_SCROLLABLE_LEGEND
+
     // Screen is only refreshed from the OnIdle handler if it is dirty.
     bool m_dirty;
     bool m_initialized;
@@ -733,6 +737,10 @@ public:
 #endif
     }
 
+#if ENABLE_SCROLLABLE_LEGEND
+    void reset_old_size() { m_old_size = { 0, 0 }; }
+#endif // ENABLE_SCROLLABLE_LEGEND
+
 private:
     bool _is_shown_on_screen() const;