1 files changed, 37 insertions, 0 deletions
diff --git a/include/cru/ui/render/render_object.hpp b/include/cru/ui/render/render_object.hpp
index dca254cc..8ea7ca79 100644
--- a/include/cru/ui/render/render_object.hpp
+++ b/include/cru/ui/render/render_object.hpp
@@ -15,6 +15,18 @@ class Painter;
 }
 
 namespace cru::ui::render {
+struct IRenderHost : Interface {
+  // Mark the layout as invalid, and arrange a re-layout later.
+  // Note this method might be called more than one times in a message cycle. So
+  // implementation should merge multiple request into once.
+  virtual void InvalidateLayout() = 0;
+
+  // Mark the paint as invalid, and arrange a re-paint later.
+  // Note this method might be called more than one times in a message cycle. So
+  // implementation should merge multiple request into once.
+  virtual void InvalidatePaint() = 0;
+};
+
 class RenderObject : public Object {
  protected:
   RenderObject() = default;
@@ -29,6 +41,9 @@ class RenderObject : public Object {
   Control* GetAttachedControl() const { return control_; }
   void SetAttachedControl(Control* new_control) { control_ = new_control; }
 
+  IRenderHost* GetRenderHost() const { return render_host_; }
+  void SetRenderHost(IRenderHost* render_host) { render_host_ = render_host; }
+
   RenderObject* GetParent() const { return parent_; }
 
   const std::vector<RenderObject*>& GetChildren() const { return children_; }
@@ -63,10 +78,29 @@ class RenderObject : public Object {
   virtual RenderObject* HitTest(const Point& point) = 0;
 
  protected:
+  enum class ChildMode {
+    None,
+    Single,
+    Multiple,
+  };
+
+  void SetChildMode(ChildMode mode) { child_mode_ = mode; }
+
+  void InvalidateLayout() const {
+    if (render_host_ != nullptr) render_host_->InvalidateLayout();
+  }
+
+  void InvalidatePaint() const {
+    if (render_host_ != nullptr) render_host_->InvalidatePaint();
+  }
+
+ protected:
   virtual void OnParentChanged(RenderObject* old_parent,
                                RenderObject* new_parent);
 
+  // default is to invalidate both layout and paint
   virtual void OnAddChild(RenderObject* new_child, int position);
+  // default is to invalidate both layout and paint
   virtual void OnRemoveChild(RenderObject* removed_child, int position);
 
   virtual void OnSizeChanged(const Size& old_size, const Size& new_size);
@@ -83,10 +117,13 @@ class RenderObject : public Object {
 
  private:
   Control* control_ = nullptr;
+  IRenderHost* render_host_ = nullptr;
 
   RenderObject* parent_ = nullptr;
   std::vector<RenderObject*> children_{};
 
+  ChildMode child_mode_ = ChildMode::None;
+
   Point offset_{};
   Size size_{};