Implement ScrollRenderObject::ScrollToContain .

2 files changed, 18 insertions, 0 deletions

diff --git a/include/cru/platform/GraphBase.hpp b/include/cru/platform/GraphBase.hpp
index 28dab1e6..e476e3cd 100644
--- a/include/cru/platform/GraphBase.hpp
+++ b/include/cru/platform/GraphBase.hpp
@@ -161,6 +161,12 @@ struct Rect final {
 
   constexpr Size GetSize() const { return Size(width, height); }
 
+  constexpr Rect Expand(const Thickness& thickness) const {
+    return Rect(left - thickness.left, top - thickness.top,
+                width + thickness.GetHorizontalTotal(),
+                height + thickness.GetVerticalTotal());
+  }
+
   constexpr Rect Shrink(const Thickness& thickness) const {
     return Rect(left + thickness.left, top + thickness.top,
                 width - thickness.GetHorizontalTotal(),
diff --git a/include/cru/ui/render/ScrollRenderObject.hpp b/include/cru/ui/render/ScrollRenderObject.hpp
index 45fa3993..9b0cbf9a 100644
--- a/include/cru/ui/render/ScrollRenderObject.hpp
+++ b/include/cru/ui/render/ScrollRenderObject.hpp
@@ -3,6 +3,8 @@
 
 #include "cru/platform/graph/util/Painter.hpp"
 
+#include <optional>
+
 namespace cru::ui::render {
 // Measure logic:
 // Measure child with unspecified min and max size.
@@ -26,9 +28,19 @@ class ScrollRenderObject : public RenderObject {
   // Return the coerced scroll offset.
   Point GetScrollOffset();
   void SetScrollOffset(const Point& offset);
+  void SetScrollOffset(std::optional<float> x, std::optional<float> y);
   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{});
 
  protected: