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1 files changed, 98 insertions, 0 deletions

diff --git a/include/cru/ui/render/ScrollRenderObject.h b/include/cru/ui/render/ScrollRenderObject.h
new file mode 100644
index 00000000..bb282953
--- /dev/null
+++ b/include/cru/ui/render/ScrollRenderObject.h
@@ -0,0 +1,98 @@
+#pragma once
+#include "RenderObject.h"
+
+#include "cru/common/Event.h"
+#include "cru/platform/graphics/util/Painter.h"
+#include "cru/ui/Base.h"
+#include "cru/ui/render/ScrollBar.h"
+
+#include <memory>
+#include <optional>
+
+namespace cru::ui::render {
+// Measure logic:
+// Measure child with unspecified min and max size.
+// If parent's preferred size is specified, then it is used as measure result.
+// Or child's size is coerced into requirement and then used as result.
+// If no child, then use the preferred size if set or min size if set or 0.
+// Layout logic:
+// If child is smaller than content area, layout at lefttop.
+// Or layout by scroll state.
+class CRU_UI_API ScrollRenderObject : public RenderObject {
+ public:
+  ScrollRenderObject();
+
+  CRU_DELETE_COPY(ScrollRenderObject)
+  CRU_DELETE_MOVE(ScrollRenderObject)
+
+  ~ScrollRenderObject() override = default;
+
+  RenderObject* HitTest(const Point& point) override;
+
+  // Return the coerced scroll offset.
+  Point GetScrollOffset();
+  float GetScrollOffset(Direction direction) {
+    return direction == Direction::Horizontal ? GetScrollOffset().x
+                                              : GetScrollOffset().y;
+  }
+  void SetScrollOffset(const Point& offset);
+  void SetScrollOffset(std::optional<float> x, std::optional<float> y);
+  void SetScrollOffset(Direction direction, std::optional<float> value) {
+    if (direction == Direction::Horizontal) {
+      SetScrollOffset(value, std::nullopt);
+    } else {
+      SetScrollOffset(std::nullopt, value);
+    }
+  }
+
+  void ApplyScroll(const Scroll& scroll);
+
+  Point GetRawScrollOffset() const { return scroll_offset_; }
+
+  // Return the viewable area rect.
+  // Lefttop is scroll offset. Size is content size.
+  // If size exceeds view area, left and top is more important when calculate
+  // new scroll offset.
+  Rect GetViewRect() {
+    return Rect{GetScrollOffset(), GetContentRect().GetSize()};
+  }
+
+  // Rect lefttop relative to content rect.
+  // Param margin is just for convenience and it will just add to the rect.
+  void ScrollToContain(const Rect& rect, const Thickness& margin = Thickness{});
+
+  std::u16string_view GetName() const override { return u"ScrollRenderObject"; }
+
+  bool IsMouseWheelScrollEnabled() const { return is_mouse_wheel_enabled_; }
+  void SetMouseWheelScrollEnabled(bool enable);
+
+  bool HorizontalCanScrollUp();
+  bool HorizontalCanScrollDown();
+  bool VerticalCanScrollUp();
+  bool VerticalCanScrollDown();
+
+ protected:
+  void OnDrawCore(platform::graphics::IPainter* painter) override;
+
+  // Logic:
+  // If available size is bigger than child's preferred size, then child's
+  // preferred size is taken.
+  // If not, all available size is taken while forming a scroll area.
+  Size OnMeasureContent(const MeasureRequirement& requirement,
+                        const MeasureSize& preferred_size) override;
+  void OnLayoutContent(const Rect& content_rect) override;
+
+  void OnAttachedControlChanged(controls::Control* control) override;
+
+  void InstallMouseWheelHandler(controls::Control* control);
+
+ private:
+  Point scroll_offset_;
+
+  std::unique_ptr<ScrollBarDelegate> scroll_bar_delegate_;
+
+  bool is_mouse_wheel_enabled_ = true;
+
+  EventRevokerListGuard guard_;
+};
+}  // namespace cru::ui::render