diff --git a/ui/README.md b/ui/README.md
index e8dcb499..83db6373 100644
--- a/ui/README.md
+++ b/ui/README.md
@@ -114,6 +114,7 @@
 - 继续收窄候选窗顶部 `ni` 文本自身的占位宽度，避免 caret 虽然间距设小了但仍被文本槽位视觉上推远
 - `Button` 点击后不再残留焦点高亮边框，保留按下态但去掉持续的描边强调
 - `PopupHost` 现在会把按下/抬起鼠标事件转发给内部 trigger，因此像 `Open Quick Actions` 这样的弹层按钮也会显示正常的点击反馈
+- `Popup` 新增是否限制在视口内的开关；demo 里的页面内弹层已关闭该限制，因此滚动页面时弹出框会跟随锚点自然滚出可视区，而不是停在窗口边缘
 - `CandidateList` 现支持基础键盘导航：弹层打开后会自动把焦点落到首个可聚焦内容上，候选列表可用 `Up/Down`、`Left/Right`、`Home/End`、`PageUp/PageDown` 切换高亮项
 - demo 中的候选窗预览继续补上了底部分页/状态提示区，用来预演候选页码、当前高亮项和键盘操作提示的布局结构
 - `Window` 新增公开的 `FocusVisual` 入口，方便 popup、候选窗、上下文菜单这类 overlay 内容在弹出后主动把焦点切到内部可交互控件
diff --git a/ui/demos/msimeui-demo/DemoScene.cpp b/ui/demos/msimeui-demo/DemoScene.cpp
index 061485ac..3e6bae71 100644
--- a/ui/demos/msimeui-demo/DemoScene.cpp
+++ b/ui/demos/msimeui-demo/DemoScene.cpp
@@ -413,6 +413,7 @@ std::unique_ptr<Scene> CreateDemoScene()
 
     auto popup = std::make_shared<Popup>(popupContent);
     popup->SetMatchAnchorWidth(false);
+    popup->SetConstrainToViewport(false);
     popup->SetWidth(300.0f);
     popup->SetPadding({18.0f, 18.0f, 18.0f, 18.0f});
 
@@ -503,6 +504,7 @@ std::unique_ptr<Scene> CreateDemoScene()
 
     auto candidatePopup = std::make_shared<Popup>(candidatePopupStack);
     candidatePopup->SetMatchAnchorWidth(false);
+    candidatePopup->SetConstrainToViewport(false);
     candidatePopup->SetWidth(118.0f);
     candidatePopup->SetPadding({5.0f, 2.0f, 5.0f, 2.0f});
     candidatePopup->SetBackgroundFill(D2D1::ColorF(0x252525));
diff --git a/ui/include/msimeui/Controls.h b/ui/include/msimeui/Controls.h
index 4e1ae9d3..5f451ad2 100644
--- a/ui/include/msimeui/Controls.h
+++ b/ui/include/msimeui/Controls.h
@@ -102,6 +102,7 @@ class Popup : public Visual
     void SetPlacement(PopupPlacement placement);
     void SetOffset(float x, float y);
     void SetMatchAnchorWidth(bool matchAnchorWidth);
+    void SetConstrainToViewport(bool constrainToViewport);
     void SetBackgroundFill(const D2D1_COLOR_F &fill);
     void SetBorderColor(const D2D1_COLOR_F &border);
     void SetCornerRadius(float radius);
@@ -124,6 +125,7 @@ class Popup : public Visual
     float offsetX_ = 0.0f;
     float offsetY_ = 8.0f;
     bool matchAnchorWidth_ = true;
+    bool constrainToViewport_ = true;
     D2D1_COLOR_F backgroundFill_ = D2D1::ColorF(0xFFFFFF);
     D2D1_COLOR_F borderColor_ = D2D1::ColorF(0xD6DCE5);
     float cornerRadius_ = 16.0f;
diff --git a/ui/src/Controls.cpp b/ui/src/Controls.cpp
index 2f98734c..d3e79ca2 100644
--- a/ui/src/Controls.cpp
+++ b/ui/src/Controls.cpp
@@ -526,6 +526,11 @@ void Popup::SetMatchAnchorWidth(bool matchAnchorWidth)
     matchAnchorWidth_ = matchAnchorWidth;
 }
 
+void Popup::SetConstrainToViewport(bool constrainToViewport)
+{
+    constrainToViewport_ = constrainToViewport;
+}
+
 void Popup::SetBackgroundFill(const D2D1_COLOR_F &fill)
 {
     backgroundFill_ = fill;
@@ -646,18 +651,18 @@ void Popup::LayoutOverlay(const SizeF &viewportSize)
     const float height = measured.height;
 
     float x = anchorRect_.x + offsetX_;
-    if (x + width > viewportSize.width - 8.0f)
+    if (constrainToViewport_ && x + width > viewportSize.width - 8.0f)
     {
         x = std::max(viewportSize.width - width - 8.0f, 8.0f);
     }
 
     float y = placement_ == PopupPlacement::AboveLeading ? (anchorRect_.y - height - offsetY_)
                                                          : (anchorRect_.y + anchorRect_.height + offsetY_);
-    if (placement_ == PopupPlacement::AboveLeading && y < 8.0f)
+    if (constrainToViewport_ && placement_ == PopupPlacement::AboveLeading && y < 8.0f)
     {
         y = anchorRect_.y + anchorRect_.height + offsetY_;
     }
-    if (placement_ == PopupPlacement::BelowLeading && y + height > viewportSize.height - 8.0f)
+    if (constrainToViewport_ && placement_ == PopupPlacement::BelowLeading && y + height > viewportSize.height - 8.0f)
     {
         const float aboveY = anchorRect_.y - height - offsetY_;
         if (aboveY >= 8.0f)
@@ -666,7 +671,10 @@ void Popup::LayoutOverlay(const SizeF &viewportSize)
         }
     }
 
-    y = std::clamp(y, 8.0f, std::max(viewportSize.height - height - 8.0f, 8.0f));
+    if (constrainToViewport_)
+    {
+        y = std::clamp(y, 8.0f, std::max(viewportSize.height - height - 8.0f, 8.0f));
+    }
     ArrangeInLayout({x, y, width, height});
 }