brush panel folding

src/node.h

@@ -158,6 +158,11 @@ public:
     void SetAspectRatio(float ar);
     void SetRTL(YGDirection dir);
 
+    // used in visibility switch
+    YGNodeRef y_placeholder = nullptr;
+    void SetVisibility(bool visible);
+    void ToggleVisibility();
+
     glm::vec2 GetPosition();
     float GetWidth();
     float GetHeight();