Write canvas render object layout logic.

5 files changed, 40 insertions, 2 deletions

diff --git a/include/cru/ui/render/canvas_render_object.hpp b/include/cru/ui/render/canvas_render_object.hpp
index 5fea8755..e3388014 100644
--- a/include/cru/ui/render/canvas_render_object.hpp
+++ b/include/cru/ui/render/canvas_render_object.hpp
@@ -21,6 +21,9 @@ class CanvasPaintEventArgs {
   Rect paint_rect_;
 };
 
+// The measure logic for `CanvasRenderObject` is that you set a desired size by
+// `SetDesiredSize` (not `SetPreferredSize`) and it will compare desired size
+// and available size and use the smaller one (by `Min`).
 class CanvasRenderObject : public RenderObject {
  public:
   CanvasRenderObject();
@@ -35,6 +38,12 @@ class CanvasRenderObject : public RenderObject {
 
   RenderObject* HitTest(const Point& point) override;
 
+  Size GetDesiredSize() const { return desired_size_; }
+
+  // Set the desired size. This is the content size excluding padding and
+  // margin.
+  void SetDesiredSize(const Size& new_size) { desired_size_ = new_size; }
+
   IEvent<CanvasPaintEventArgs>* PaintEvent() { return &paint_event_; }
 
  protected:
@@ -42,6 +51,8 @@ class CanvasRenderObject : public RenderObject {
   void OnLayoutContent(const Rect& content_rect) override;
 
  private:
+  Size desired_size_{};
+
   Event<CanvasPaintEventArgs> paint_event_;
 };
 }  // namespace cru::ui::render
diff --git a/include/cru/ui/render/layout_utility.hpp b/include/cru/ui/render/layout_utility.hpp
new file mode 100644
index 00000000..38191ad5
--- /dev/null
+++ b/include/cru/ui/render/layout_utility.hpp
@@ -0,0 +1,6 @@
+#include "../base.hpp"
+
+namespace cru::ui::render {
+  Size Min(const Size& left, const Size& right);
+  Size Max(const Size& left, const Size& right);
+}
diff --git a/src/ui/CMakeLists.txt b/src/ui/CMakeLists.txt
index cb34e590..2220740e 100644
--- a/src/ui/CMakeLists.txt
+++ b/src/ui/CMakeLists.txt
@@ -21,6 +21,7 @@ add_library(cru_ui STATIC
     render/border_render_object.cpp
     render/canvas_render_object.cpp
     render/flex_layout_render_object.cpp
+    render/layout_utility.cpp
     render/render_object.cpp
     render/stack_layout_render_object.cpp
     render/text_render_object.cpp
@@ -46,6 +47,7 @@ target_sources(cru_ui PUBLIC
 	${CRU_UI_INCLUDE_DIR}/render/canvas_render_object.hpp
 	${CRU_UI_INCLUDE_DIR}/render/flex_layout_render_object.hpp
 	${CRU_UI_INCLUDE_DIR}/render/layout_render_object.hpp
+	${CRU_UI_INCLUDE_DIR}/render/layout_utility.hpp
 	${CRU_UI_INCLUDE_DIR}/render/render_object.hpp
     ${CRU_UI_INCLUDE_DIR}/render/stack_layout_render_object.hpp
 	${CRU_UI_INCLUDE_DIR}/render/text_render_object.hpp
diff --git a/src/ui/render/canvas_render_object.cpp b/src/ui/render/canvas_render_object.cpp
index 0a442317..0508e276 100644
--- a/src/ui/render/canvas_render_object.cpp
+++ b/src/ui/render/canvas_render_object.cpp
@@ -1,5 +1,7 @@
 #include "cru/ui/render/canvas_render_object.hpp"
 
+#include "cru/ui/render/layout_utility.hpp"
+
 namespace cru::ui::render {
 CanvasRenderObject::CanvasRenderObject() : RenderObject(ChildMode::None) {}
 
@@ -17,8 +19,10 @@ RenderObject* CanvasRenderObject::HitTest(const Point& point) {
 }
 
 Size CanvasRenderObject::OnMeasureContent(const Size& available_size) {
-  return Size{};
+  return Min(available_size, GetDesiredSize());
 }
 
-void CanvasRenderObject::OnLayoutContent(const Rect& content_rect) {}
+void CanvasRenderObject::OnLayoutContent(const Rect& content_rect) {
+  CRU_UNUSED(content_rect)
+}
 }  // namespace cru::ui::render
diff --git a/src/ui/render/layout_utility.cpp b/src/ui/render/layout_utility.cpp
new file mode 100644
index 00000000..aae62d35
--- /dev/null
+++ b/src/ui/render/layout_utility.cpp
@@ -0,0 +1,15 @@
+#include "cru/ui/render/layout_utility.hpp"
+
+#include <algorithm>
+
+namespace cru::ui::render {
+Size Min(const Size& left, const Size& right) {
+  return Size{std::min(left.width, right.width),
+              std::min(left.height, right.height)};
+}
+
+Size Max(const Size& left, const Size& right) {
+  return Size{std::max(left.width, right.width),
+              std::max(left.height, right.height)};
+}
+}  // namespace cru::ui::render