Implement ScrollRenderObject::ScrollToContain .

3 files changed, 57 insertions, 4 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:
diff --git a/src/ui/render/ScrollRenderObject.cpp b/src/ui/render/ScrollRenderObject.cpp
index 533a269a..08ce744b 100644
--- a/src/ui/render/ScrollRenderObject.cpp
+++ b/src/ui/render/ScrollRenderObject.cpp
@@ -67,12 +67,47 @@ void ScrollRenderObject::SetScrollOffset(const Point& offset) {
   InvalidateLayout();
 }
 
+void ScrollRenderObject::SetScrollOffset(std::optional<float> x,
+                                         std::optional<float> y) {
+  bool dirty = false;
+
+  if (x.has_value()) {
+    dirty = true;
+    scroll_offset_.x = *x;
+  }
+
+  if (y.has_value()) {
+    dirty = true;
+    scroll_offset_.y = *y;
+  }
+
+  if (dirty) InvalidateLayout();
+}
+
 void ScrollRenderObject::ScrollToContain(const Rect& rect,
                                          const Thickness& margin) {
-  // TODO: Implement this.
-  CRU_UNUSED(rect);
-  CRU_UNUSED(margin);
-  throw std::runtime_error("Not implemented.");
+  std::optional<float> new_scroll_x;
+  std::optional<float> new_scroll_y;
+
+  Rect real_rect = rect.Expand(margin);
+
+  Rect view_rect = GetViewRect();
+
+  // horizontal
+  if (real_rect.left < view_rect.left) {
+    new_scroll_x = real_rect.left;
+  } else if (real_rect.GetRight() > view_rect.GetRight()) {
+    new_scroll_x = real_rect.GetRight() - view_rect.width;
+  }
+
+  // vertical
+  if (real_rect.top < view_rect.top) {
+    new_scroll_y = real_rect.top;
+  } else if (real_rect.GetBottom() > view_rect.GetBottom()) {
+    new_scroll_y = real_rect.GetBottom() - view_rect.height;
+  }
+
+  SetScrollOffset(new_scroll_x, new_scroll_y);
 }
 
 Size ScrollRenderObject::OnMeasureContent(const MeasureRequirement& requirement,