5 files changed, 61 insertions, 11 deletions

diff --git a/src/base.h b/src/base.h
index c8866cf6..9b3b50a1 100644
--- a/src/base.h
+++ b/src/base.h
@@ -10,6 +10,7 @@
 #include <memory>
 #include <string_view>
 #include <chrono>
+#include <optional>
 
 namespace cru
 {
@@ -63,4 +64,31 @@ namespace cru
         if (!condition)
             throw std::invalid_argument(error_message.data());
     }
+
+    template <typename T, typename = std::enable_if_t<std::is_arithmetic_v<T>>>
+    float Coerce(const T n, const std::optional<T> min, const std::optional<T> max)
+    {
+        if (min.has_value() && n < min.value())
+            return min.value();
+        if (max.has_value() && n > max.value())
+            return max.value();
+        return n;
+    }
+
+    template <typename T, typename = std::enable_if_t<std::is_arithmetic_v<T>>>
+    float Coerce(const T n, const std::nullopt_t, const std::optional<T> max)
+    {
+        if (max.has_value() && n > max.value())
+            return max.value();
+        return n;
+    }
+
+    template <typename T, typename = std::enable_if_t<std::is_arithmetic_v<T>>>
+    float Coerce(const T n, const std::optional<T> min, const std::nullopt_t)
+    {
+        if (min.has_value() && n < min.value())
+            return min.value();
+        return n;
+    }
+
 }
diff --git a/src/main.cpp b/src/main.cpp
index a15fa4da..5fd59ede 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -129,6 +129,13 @@ int APIENTRY wWinMain(
     }
 
     {
+        const auto text_box = TextBox::Create();
+        text_box->GetLayoutParams()->width.min = 50.0f;
+        text_box->GetLayoutParams()->width.max = 100.0f;
+        layout->AddChild(text_box);
+    }
+
+    {
         const auto text_block = CreateWithLayout<TextBlock>(LayoutSideParams::Stretch(), LayoutSideParams::Stretch(), L"This is a very very very very very long sentence!!!");
         text_block->SetSelectable(true);
         layout->AddChild(text_block);
diff --git a/src/ui/control.cpp b/src/ui/control.cpp
index 79def066..9416d48a 100644
--- a/src/ui/control.cpp
+++ b/src/ui/control.cpp
@@ -689,11 +689,6 @@ namespace cru {
             return value < 0 ? 0 : value;
         }
 
-        inline Size AtLeast0(const Size& size)
-        {
-            return Size(AtLeast0(size.width), AtLeast0(size.height));
-        }
-
         Size Control::OnMeasureCore(const Size& available_size)
         {
             const auto layout_params = GetLayoutParams();
@@ -715,11 +710,14 @@ namespace cru {
 
             auto&& get_content_measure_length = [](const LayoutSideParams& layout_length, const float available_length, const float outer_length) -> float
             {
+                float length;
                 if (layout_length.mode == MeasureMode::Exactly)
-                    return layout_length.length;
-                if (available_length > outer_length)
-                    return available_length - outer_length;
-                return 0.0;
+                    length = layout_length.length;
+                else if (available_length > outer_length)
+                    length = available_length - outer_length;
+                else
+                    length = 0;
+                return Coerce(length, layout_length.min, layout_length.max);
             };
 
             // if padding, margin and border exceeded, then content size is 0.
@@ -735,7 +733,7 @@ namespace cru {
                 // only use measure length when stretch and actual length is smaller than measure length, that is "stretch"
                 if (layout_length.mode == MeasureMode::Stretch && actual_length < measure_length)
                     return measure_length;
-                return actual_length;
+                return Coerce(actual_length, layout_length.min, std::nullopt);
             };
 
             const auto final_size = Size(
diff --git a/src/ui/controls/linear_layout.h b/src/ui/controls/linear_layout.h
index 1c2232bb..021f4b7d 100644
--- a/src/ui/controls/linear_layout.h
+++ b/src/ui/controls/linear_layout.h
@@ -4,6 +4,8 @@
 
 namespace cru::ui::controls
 {
+    // Min length of main side in layout params is of no meaning.
+    // All children will layout from start and redundant length is blank.
     class LinearLayout : public Control
     {
     public:
diff --git a/src/ui/layout_base.h b/src/ui/layout_base.h
index 662210bd..4a4c09ea 100644
--- a/src/ui/layout_base.h
+++ b/src/ui/layout_base.h
@@ -101,12 +101,27 @@ namespace cru
 
             constexpr bool Validate() const
             {
-                return length >= 0.0;
+                if (length < 0.0)
+                    return false;
+                if (min.has_value() && min.value() < 0.0)
+                    return false;
+                if (max.has_value() && max.value() < 0.0)
+                    return false;
+                if (min.has_value() && max.has_value() && min.value() > max.value())
+                    return false;
+                return true;
             }
 
+            // only used in exactly mode, specify the exactly side length of content.
             float length = 0.0;
             MeasureMode mode = MeasureMode::Content;
             Alignment alignment = Alignment::Center;
+
+            // min and max specify the min/max side length of content.
+            // they are used as hint and respect the actual size that content needs.
+            // when mode is exactly, length is coerced into the min-max range.
+            std::optional<float> min = std::nullopt;
+            std::optional<float> max = std::nullopt;
         };
 
         struct BasicLayoutParams final