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1 files changed, 77 insertions, 0 deletions

diff --git a/src/ui/render/ScrollRenderObject.cpp b/src/ui/render/ScrollRenderObject.cpp
index 33e9e407..f1df9d8b 100644
--- a/src/ui/render/ScrollRenderObject.cpp
+++ b/src/ui/render/ScrollRenderObject.cpp
@@ -1 +1,78 @@
 #include "cru/ui/render/ScrollRenderObject.hpp"
+
+#include "cru/platform/graph/Painter.hpp"
+#include "cru/platform/graph/util/Painter.hpp"
+
+#include <algorithm>
+
+namespace cru::ui::render {
+namespace {
+// This method assumes margin offset is already considered.
+// It promises that it won't return negetive value.
+Point CalculateChildOffsetOfScroll(const Point& scroll_offset,
+                                   const Size& content_area_size,
+                                   const Thickness& padding,
+                                   const Size& child_size) {
+  Point result(scroll_offset);
+
+  Point max_scroll(child_size - content_area_size);
+  max_scroll.x = std::max(max_scroll.x, 0.f);
+  max_scroll.y = std::max(max_scroll.y, 0.f);
+
+  auto coerce = [](float& n, float max) {
+    if (n < 0)
+      n = 0;
+    else if (n > max)
+      n = max;
+  };
+
+  coerce(result.x, scroll_offset.x);
+  coerce(result.y, scroll_offset.y);
+
+  result.x += padding.left;
+  result.y += padding.top;
+
+  return result;
+}
+}  // namespace
+
+void ScrollRenderObject::Draw(platform::graph::IPainter* painter) {
+  for (auto child : this->GetChildren()) {
+    painter->PushLayer(this->GetPaddingRect());
+    const auto true_offset =
+        CalculateChildOffsetOfScroll(scroll_offset_, GetContentRect().GetSize(),
+                                     GetPadding(), child->GetSize());
+    platform::graph::util::WithTransform(
+        painter, Matrix::Translation(true_offset.x, true_offset.y),
+        [child](platform::graph::IPainter* p) { child->Draw(p); });
+    painter->PopLayer();
+  }
+}
+
+RenderObject* ScrollRenderObject::HitTest(const Point& point) {
+  const auto rect = GetPaddingRect();
+  return rect.IsPointInside(point) ? this : nullptr;
+}
+
+void ScrollRenderObject::SetScrollOffset(const Point& offset) {
+  scroll_offset_ = offset;
+  InvalidatePaint();
+}
+
+Size ScrollRenderObject::OnMeasureContent(
+    const MeasureRequirement& requirement) {
+  CRU_UNUSED(requirement);
+  // TODO!
+  // const auto& children = GetChildren();
+  // if (children.empty()) return Size{};
+  // const auto child = children.front();
+  // child->Measure(MeasureRequirement::Infinate());
+  // const auto preferred_size = child->GetMeasuredSize();
+  return Size{};
+}  // namespace cru::ui::render
+
+void ScrollRenderObject::OnLayoutContent(const Rect& content_rect) {
+  CRU_UNUSED(content_rect);
+  // TODO!
+}
+}  // namespace cru::ui::render