3 files changed, 34 insertions, 7 deletions
diff --git a/include/cru/ui/render/FlexLayoutRenderObject.hpp b/include/cru/ui/render/FlexLayoutRenderObject.hpp
index 83d1e268..4b1e079d 100644
--- a/include/cru/ui/render/FlexLayoutRenderObject.hpp
+++ b/include/cru/ui/render/FlexLayoutRenderObject.hpp
@@ -3,8 +3,9 @@
 
 namespace cru::ui::render {
 // Measure Logic (v0.1):
-// 1. Layout all children with unspecified(infinate) max main axis length. If
-// max cross axis length of parent is specified, then it is passed to children.
+// Cross axis measure logic is the same as stack layout.
+//
+// 1. Layout all children with unspecified(infinate) max main axis length.
 //
 // 2. Add up main axis length of children to get total main length.
 //
@@ -72,10 +73,6 @@ namespace cru::ui::render {
 // (if specified), then coerce the length to the min value but not report error
 // and just fill the rest space with blank.
 //
-// 5. Result cross axis length is the max cross axis length of all children. If
-// min cross axis length is specified and result length is smaller than it, then
-// result length is coerced to it.
-//
 class FlexLayoutRenderObject : public LayoutRenderObject<FlexChildLayoutData> {
  public:
   FlexLayoutRenderObject() = default;
diff --git a/include/cru/ui/render/LayoutHelper.hpp b/include/cru/ui/render/LayoutHelper.hpp
new file mode 100644
index 00000000..8536c451
--- /dev/null
+++ b/include/cru/ui/render/LayoutHelper.hpp
@@ -0,0 +1,13 @@
+#pragma once
+#include "Base.hpp"
+
+#include "MeasureRequirement.hpp"
+
+namespace cru::ui::render {
+float CalculateAnchorByAlignment(Alignment alignment, float start_point,
+                                 float content_length, float child_length);
+
+MeasureLength StackLayoutCalculateChildMaxLength(
+    MeasureLength parent_preferred_size, MeasureLength parent_max_size,
+    MeasureLength child_min_size, std::string_view exceeds_message);
+}  // namespace cru::ui::render
diff --git a/include/cru/ui/render/StackLayoutRenderObject.hpp b/include/cru/ui/render/StackLayoutRenderObject.hpp
index e89e5346..f6b4ffb7 100644
--- a/include/cru/ui/render/StackLayoutRenderObject.hpp
+++ b/include/cru/ui/render/StackLayoutRenderObject.hpp
@@ -3,7 +3,24 @@
 
 namespace cru::ui::render {
 // Measure Logic:
-// 
+// Following rules are applied both horizontally and vertically.
+//
+// 1. Measure each children with min size not specified and max size as
+// following rules:
+//
+//    1.1. If parent's preferred size is set and it is not less than child's min
+//    size, then it is used as child's max size.
+//
+//    1.2. Or if parent's max size is set, then it is used as child's max size.
+//    If it is less than child's min size, then log an warning about that.
+//
+// 2. Result size is children's max size.
+//
+// 3. If preferred size is specified and result size is smaller than it, coerce
+// result size to preferred size.
+//
+// 4. If result size is smaller than min size (if specified), coerce result size
+// to min size.
 class StackLayoutRenderObject
     : public LayoutRenderObject<StackChildLayoutData> {
  public: