views: mac: Support dynamic resize of title bar height (see #3189)

This is intended for usage with frameless windows that show the standard window
buttons, where resizing the title bar height changes the button offset. Returning a
different value from CefWindowDelegate::GetTitlebarHeight and forcing a resize of
the NSWindow's theme frame (see ViewsWindow::NudgeWindow) will update the
title bar height.

To test:
1. Run `cefclient --use-views --hide-frame --show-window-buttons --url=http://tests/window`
2. Enter a new value for title bar height and click the "Set Titlebar Height" button

19 files changed, 155 insertions, 61 deletions

diff --git a/cef_paths2.gypi b/cef_paths2.gypi
index 377b48d4..38718e4b 100644
--- a/cef_paths2.gypi
+++ b/cef_paths2.gypi
@@ -393,6 +393,7 @@
       'tests/cefclient/browser/temp_window_mac.mm',
       'tests/cefclient/browser/text_input_client_osr_mac.h',
       'tests/cefclient/browser/text_input_client_osr_mac.mm',
+      'tests/cefclient/browser/views_window_mac.mm',
       'tests/cefclient/browser/window_test_runner_mac.h',
       'tests/cefclient/browser/window_test_runner_mac.mm',
       'tests/cefclient/cefclient_mac.mm',
diff --git a/libcef/browser/views/native_widget_mac.h b/libcef/browser/views/native_widget_mac.h
index bbe22068..b4745764 100644
--- a/libcef/browser/views/native_widget_mac.h
+++ b/libcef/browser/views/native_widget_mac.h
@@ -6,15 +6,18 @@
 #define CEF_LIBCEF_BROWSER_VIEWS_NATIVE_WIDGET_MAC_H_
 #pragma once
 
-#include "third_party/abseil-cpp/absl/types/optional.h"
+#include "include/internal/cef_ptr.h"
+
 #include "ui/views/widget/native_widget_mac.h"
 
+class CefWindow;
+class CefWindowDelegate;
+
 class CefNativeWidgetMac : public views::NativeWidgetMac {
  public:
   CefNativeWidgetMac(views::internal::NativeWidgetDelegate* delegate,
-                     bool is_frameless,
-                     bool with_window_buttons,
-                     absl::optional<float> title_bar_height);
+                     CefRefPtr<CefWindow> window,
+                     CefWindowDelegate* window_delegate);
   ~CefNativeWidgetMac() override = default;
 
   CefNativeWidgetMac(const CefNativeWidgetMac&) = delete;
@@ -29,9 +32,8 @@ class CefNativeWidgetMac : public views::NativeWidgetMac {
                                     float* titlebar_height) override;
 
  private:
-  const bool is_frameless_;
-  const bool with_window_buttons_;
-  const absl::optional<float> title_bar_height_;
+  const CefRefPtr<CefWindow> window_;
+  CefWindowDelegate* const window_delegate_;
 };
 
 #endif  // CEF_LIBCEF_BROWSER_VIEWS_NATIVE_WIDGET_MAC_H_
diff --git a/libcef/browser/views/native_widget_mac.mm b/libcef/browser/views/native_widget_mac.mm
index 34ffdb1a..b722c373 100644
--- a/libcef/browser/views/native_widget_mac.mm
+++ b/libcef/browser/views/native_widget_mac.mm
@@ -4,17 +4,17 @@
 
 #include "libcef/browser/views/native_widget_mac.h"
 
+#include "include/views/cef_window.h"
+#include "include/views/cef_window_delegate.h"
 #include "libcef/browser/views/ns_window.h"
 
 CefNativeWidgetMac::CefNativeWidgetMac(
     views::internal::NativeWidgetDelegate* delegate,
-    bool is_frameless,
-    bool with_window_buttons,
-    absl::optional<float> title_bar_height)
+    CefRefPtr<CefWindow> window,
+    CefWindowDelegate* window_delegate)
     : views::NativeWidgetMac(delegate),
-      is_frameless_(is_frameless),
-      with_window_buttons_(with_window_buttons),
-      title_bar_height_(title_bar_height) {}
+      window_(window),
+      window_delegate_(window_delegate) {}
 
 NativeWidgetMacNSWindow* CefNativeWidgetMac::CreateNSWindow(
     const remote_cocoa::mojom::CreateWindowParams* params) {
@@ -22,15 +22,18 @@ NativeWidgetMacNSWindow* CefNativeWidgetMac::CreateNSWindow(
       NSWindowStyleMaskTitled | NSWindowStyleMaskMiniaturizable |
       NSWindowStyleMaskClosable | NSWindowStyleMaskResizable |
       NSWindowStyleMaskTexturedBackground;
+
+  bool is_frameless = window_delegate_->IsFrameless(window_);
+
   auto window = [[CefNSWindow alloc] initWithStyle:style_mask
-                                       isFrameless:is_frameless_];
+                                       isFrameless:is_frameless];
 
-  if (is_frameless_) {
+  if (is_frameless) {
     [window setTitlebarAppearsTransparent:YES];
     [window setTitleVisibility:NSWindowTitleHidden];
   }
 
-  if (!with_window_buttons_) {
+  if (!window_delegate_->WithStandardWindowButtons(window_)) {
     [[window standardWindowButton:NSWindowCloseButton] setHidden:YES];
     [[window standardWindowButton:NSWindowMiniaturizeButton] setHidden:YES];
     [[window standardWindowButton:NSWindowZoomButton] setHidden:YES];
@@ -42,9 +45,8 @@ NativeWidgetMacNSWindow* CefNativeWidgetMac::CreateNSWindow(
 void CefNativeWidgetMac::GetWindowFrameTitlebarHeight(
     bool* override_titlebar_height,
     float* titlebar_height) {
-  if (title_bar_height_) {
+  if (window_delegate_->GetTitlebarHeight(window_, titlebar_height)) {
     *override_titlebar_height = true;
-    *titlebar_height = title_bar_height_.value();
   } else {
     views::NativeWidgetMac::GetWindowFrameTitlebarHeight(
         override_titlebar_height, titlebar_height);
diff --git a/libcef/browser/views/view_util.h b/libcef/browser/views/view_util.h
index 2a900061..50828da9 100644
--- a/libcef/browser/views/view_util.h
+++ b/libcef/browser/views/view_util.h
@@ -9,7 +9,6 @@
 #include "include/views/cef_view.h"
 #include "include/views/cef_window.h"
 
-#include "third_party/abseil-cpp/absl/types/optional.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/view.h"
 
@@ -29,6 +28,8 @@ class NativeWidgetDelegate;
 }
 }  // namespace views
 
+class CefWindowDelegate;
+
 #define CEF_REQUIRE_VALID_RETURN(ret) \
   if (!ParentClass::IsValid())        \
     return ret;
@@ -148,9 +149,8 @@ CefWindowHandle GetWindowHandle(gfx::NativeWindow window);
 
 views::NativeWidget* CreateNativeWidget(
     views::internal::NativeWidgetDelegate* delegate,
-    bool is_frameless,
-    bool with_window_buttons,
-    absl::optional<float> title_bar_height);
+    CefRefPtr<CefWindow> window,
+    CefWindowDelegate* window_delegate);
 
 }  // namespace view_util
 
diff --git a/libcef/browser/views/view_util_aura.cc b/libcef/browser/views/view_util_aura.cc
index f58b9b3f..f28d5526 100644
--- a/libcef/browser/views/view_util_aura.cc
+++ b/libcef/browser/views/view_util_aura.cc
@@ -44,9 +44,8 @@ CefWindowHandle GetWindowHandle(gfx::NativeWindow window) {
 
 views::NativeWidget* CreateNativeWidget(
     views::internal::NativeWidgetDelegate* delegate,
-    bool is_frameless,
-    bool with_window_buttons,
-    absl::optional<float> title_bar_height) {
+    CefRefPtr<CefWindow> window,
+    CefWindowDelegate* window_delegate) {
   return nullptr;
 }
 
diff --git a/libcef/browser/views/view_util_mac.mm b/libcef/browser/views/view_util_mac.mm
index f69bf832..2bab6b47 100644
--- a/libcef/browser/views/view_util_mac.mm
+++ b/libcef/browser/views/view_util_mac.mm
@@ -47,10 +47,8 @@ CefWindowHandle GetWindowHandle(gfx::NativeWindow window) {
 
 views::NativeWidget* CreateNativeWidget(
     views::internal::NativeWidgetDelegate* delegate,
-    bool is_frameless,
-    bool with_window_buttons,
-    absl::optional<float> title_bar_height) {
-  return new CefNativeWidgetMac(delegate, is_frameless, with_window_buttons,
-                                title_bar_height);
+    CefRefPtr<CefWindow> window,
+    CefWindowDelegate* window_delegate) {
+  return new CefNativeWidgetMac(delegate, window, window_delegate);
 }
 }  // namespace view_util
diff --git a/libcef/browser/views/window_view.cc b/libcef/browser/views/window_view.cc
index 4bf06c66..0c5ee9eb 100644
--- a/libcef/browser/views/window_view.cc
+++ b/libcef/browser/views/window_view.cc
@@ -313,13 +313,8 @@ void CefWindowView::CreateWidget(gfx::AcceleratedWidget parent_widget) {
     } else {
       is_frameless_ = cef_delegate()->IsFrameless(cef_window);
 
-      const bool with_standard_buttons =
-          cef_delegate()->WithStandardWindowButtons(cef_window);
-
-      const auto title_bar_height = GetTitlebarHeight(cef_window);
-
-      params.native_widget = view_util::CreateNativeWidget(
-          widget, is_frameless_, with_standard_buttons, title_bar_height);
+      params.native_widget =
+          view_util::CreateNativeWidget(widget, cef_window, cef_delegate());
 
       can_resize = cef_delegate()->CanResize(cef_window);
 
@@ -666,14 +661,3 @@ views::NonClientFrameView* CefWindowView::GetNonClientFrameView() const {
   }
   return widget->non_client_view()->frame_view();
 }
-
-absl::optional<float> CefWindowView::GetTitlebarHeight(
-    const CefRefPtr<CefWindow>& window) const {
-  float title_bar_height = 0;
-  const bool has_title_bar_height =
-      cef_delegate()->GetTitlebarHeight(window, &title_bar_height);
-  if (has_title_bar_height) {
-    return title_bar_height;
-  }
-  return absl::nullopt;
-}
\ No newline at end of file
diff --git a/libcef/browser/views/window_view.h b/libcef/browser/views/window_view.h
index 5b52a3f3..6789636b 100644
--- a/libcef/browser/views/window_view.h
+++ b/libcef/browser/views/window_view.h
@@ -14,7 +14,6 @@
 #include "libcef/browser/views/overlay_view_host.h"
 #include "libcef/browser/views/panel_view.h"
 
-#include "third_party/abseil-cpp/absl/types/optional.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/display/display.h"
 #include "ui/views/widget/widget_delegate.h"
@@ -120,9 +119,6 @@ class CefWindowView
 
   void MoveOverlaysIfNecessary();
 
-  absl::optional<float> GetTitlebarHeight(
-      const CefRefPtr<CefWindow>& window) const;
-
   // Not owned by this object.
   Delegate* window_delegate_;
 
diff --git a/tests/cefclient/browser/root_window_views.cc b/tests/cefclient/browser/root_window_views.cc
index 973a81c8..a8e6ff1c 100644
--- a/tests/cefclient/browser/root_window_views.cc
+++ b/tests/cefclient/browser/root_window_views.cc
@@ -28,6 +28,12 @@ RootWindowViews::~RootWindowViews() {
   REQUIRE_MAIN_THREAD();
 }
 
+void RootWindowViews::SetTitlebarHeight(const std::optional<float>& height) {
+  if (window_) {
+    window_->SetTitlebarHeight(height);
+  }
+}
+
 void RootWindowViews::Init(RootWindow::Delegate* delegate,
                            std::unique_ptr<RootWindowConfig> config,
                            const CefBrowserSettings& settings) {
diff --git a/tests/cefclient/browser/root_window_views.h b/tests/cefclient/browser/root_window_views.h
index d282f604..75997e1a 100644
--- a/tests/cefclient/browser/root_window_views.h
+++ b/tests/cefclient/browser/root_window_views.h
@@ -26,6 +26,8 @@ class RootWindowViews : public RootWindow,
   RootWindowViews();
   ~RootWindowViews();
 
+  void SetTitlebarHeight(const std::optional<float>& height);
+
   // RootWindow methods:
   void Init(RootWindow::Delegate* delegate,
             std::unique_ptr<RootWindowConfig> config,
diff --git a/tests/cefclient/browser/views_window.cc b/tests/cefclient/browser/views_window.cc
index fc6f09c0..a466047e 100644
--- a/tests/cefclient/browser/views_window.cc
+++ b/tests/cefclient/browser/views_window.cc
@@ -399,6 +399,16 @@ bool ViewsWindow::GetWindowRestorePreferences(
   return true;
 }
 
+void ViewsWindow::SetTitlebarHeight(const std::optional<float>& height) {
+  CEF_REQUIRE_UI_THREAD();
+  if (height.has_value()) {
+    override_titlebar_height_ = height;
+  } else {
+    override_titlebar_height_ = default_titlebar_height_;
+  }
+  NudgeWindow();
+}
+
 CefRefPtr<CefBrowserViewDelegate> ViewsWindow::GetDelegateForPopupBrowserView(
     CefRefPtr<CefBrowserView> browser_view,
     const CefBrowserSettings& settings,
@@ -735,8 +745,8 @@ bool ViewsWindow::GetTitlebarHeight(CefRefPtr<CefWindow> window,
                                     float* titlebar_height) {
   CEF_REQUIRE_UI_THREAD();
 #if defined(OS_MAC)
-  if (frameless_ && with_standard_buttons_) {
-    *titlebar_height = kTitleBarHeight;
+  if (override_titlebar_height_.has_value()) {
+    *titlebar_height = override_titlebar_height_.value();
     return true;
   }
 #endif
@@ -925,6 +935,13 @@ ViewsWindow::ViewsWindow(Delegate* delegate,
   // If window has frame or flag passed explicitly
   with_standard_buttons_ = !frameless_ || show_window_buttons;
 
+#if defined(OS_MAC)
+  if (frameless_ && with_standard_buttons_) {
+    default_titlebar_height_ = kTitleBarHeight;
+    override_titlebar_height_ = kTitleBarHeight;
+  }
+#endif
+
   const std::string& toolbar_type =
       command_line->GetSwitchValue(switches::kShowChromeToolbar);
   chrome_toolbar_type_ = CalculateChromeToolbarType(toolbar_type, hide_toolbar,
@@ -1262,4 +1279,10 @@ void ViewsWindow::OnExtensionWindowClosed() {
   extension_button_pressed_lock_ = nullptr;
 }
 
+#if !defined(OS_MAC)
+void ViewsWindow::NudgeWindow() {
+  NOTIMPLEMENTED();
+}
+#endif
+
 }  // namespace client
diff --git a/tests/cefclient/browser/views_window.h b/tests/cefclient/browser/views_window.h
index 14c97446..9dc34ada 100644
--- a/tests/cefclient/browser/views_window.h
+++ b/tests/cefclient/browser/views_window.h
@@ -130,6 +130,7 @@ class ViewsWindow : public CefBrowserViewDelegate,
 
   bool GetWindowRestorePreferences(cef_show_state_t& show_state,
                                    std::optional<CefRect>& dip_bounds);
+  void SetTitlebarHeight(const std::optional<float>& height);
 
   // CefBrowserViewDelegate methods:
   CefRefPtr<CefBrowserViewDelegate> GetDelegateForPopupBrowserView(
@@ -236,6 +237,8 @@ class ViewsWindow : public CefBrowserViewDelegate,
                               const ImageCache::ImageSet& images);
   void OnExtensionWindowClosed();
 
+  void NudgeWindow();
+
   Delegate* delegate_;  // Not owned by this object.
   CefRefPtr<CefBrowserView> browser_view_;
   bool frameless_;
@@ -258,6 +261,9 @@ class ViewsWindow : public CefBrowserViewDelegate,
 
   CefRefPtr<ViewsOverlayControls> overlay_controls_;
 
+  std::optional<float> default_titlebar_height_;
+  std::optional<float> override_titlebar_height_;
+
   // Structure representing an extension.
   struct ExtensionInfo {
     ExtensionInfo(CefRefPtr<CefExtension> extension, CefRefPtr<CefImage> image)
diff --git a/tests/cefclient/browser/views_window_mac.mm b/tests/cefclient/browser/views_window_mac.mm
new file mode 100644
index 00000000..936a85c0
--- /dev/null
+++ b/tests/cefclient/browser/views_window_mac.mm
@@ -0,0 +1,24 @@
+// Copyright (c) 2023 The Chromium Embedded Framework Authors. All rights
+// reserved. Use of this source code is governed by a BSD-style license that
+// can be found in the LICENSE file.
+
+#include "tests/cefclient/browser/views_window.h"
+
+#include <Cocoa/Cocoa.h>
+
+namespace client {
+
+void ViewsWindow::NudgeWindow() {
+  if (window_) {
+    auto view = CAST_CEF_WINDOW_HANDLE_TO_NSVIEW(window_->GetWindowHandle());
+    NSWindow* main_window = view.window;
+
+    auto theme_frame = main_window.contentView.superview;
+    // Nudge view frame a little to force an update.
+    NSSize size = theme_frame.frame.size;
+    [theme_frame setFrameSize:NSMakeSize(size.width - 1, size.height)];
+    [theme_frame setFrameSize:size];
+  }
+}
+
+}
diff --git a/tests/cefclient/browser/window_test.cc b/tests/cefclient/browser/window_test.cc
index 172a2243..316f6147 100644
--- a/tests/cefclient/browser/window_test.cc
+++ b/tests/cefclient/browser/window_test.cc
@@ -35,6 +35,7 @@ const char kMessagePositionName[] = "WindowTest.Position";
 const char kMessageMinimizeName[] = "WindowTest.Minimize";
 const char kMessageMaximizeName[] = "WindowTest.Maximize";
 const char kMessageRestoreName[] = "WindowTest.Restore";
+const char kMessageTitlebarHeightName[] = "WindowTest.TitlebarHeight";
 
 // Create the appropriate platform test runner object.
 std::unique_ptr<WindowTestRunner> CreateWindowTestRunner() {
@@ -69,6 +70,15 @@ std::vector<int> ParsePosition(const std::string& message_name) {
   return vec;
 }
 
+std::optional<float> ParseHeight(const std::string& message) {
+  if (message.size() > sizeof(kMessageTitlebarHeightName)) {
+    const std::string& val = message.substr(sizeof(kMessageTitlebarHeightName));
+    return std::stof(val);
+  } else {
+    return std::nullopt;
+  }
+}
+
 // Handle messages in the browser process.
 class Handler : public CefMessageRouterBrowserSide::Handler {
  public:
@@ -91,18 +101,17 @@ class Handler : public CefMessageRouterBrowserSide::Handler {
     if (message_name.find(kMessagePositionName) == 0) {
       const auto vec = ParsePosition(message_name);
       if (vec.size() == 4) {
-        // Execute SetPos() on the main thread.
         runner_->SetPos(browser, vec[0], vec[1], vec[2], vec[3]);
       }
     } else if (message_name == kMessageMinimizeName) {
-      // Execute Minimize() on the main thread.
       runner_->Minimize(browser);
     } else if (message_name == kMessageMaximizeName) {
-      // Execute Maximize() on the main thread.
       runner_->Maximize(browser);
     } else if (message_name == kMessageRestoreName) {
-      // Execute Restore() on the main thread.
       runner_->Restore(browser);
+    } else if (message_name.find(kMessageTitlebarHeightName) == 0) {
+      const auto height = ParseHeight(message_name);
+      runner_->SetTitleBarHeight(browser, height);
     } else {
       NOTREACHED();
     }
diff --git a/tests/cefclient/browser/window_test_runner.cc b/tests/cefclient/browser/window_test_runner.cc
index b410812f..c3edce6f 100644
--- a/tests/cefclient/browser/window_test_runner.cc
+++ b/tests/cefclient/browser/window_test_runner.cc
@@ -36,5 +36,10 @@ void WindowTestRunner::ModifyBounds(const CefRect& display, CefRect& window) {
   }
 }
 
+void WindowTestRunner::SetTitleBarHeight(CefRefPtr<CefBrowser> browser,
+                                         const std::optional<float>& height) {
+  NOTIMPLEMENTED();
+}
+
 }  // namespace window_test
 }  // namespace client
diff --git a/tests/cefclient/browser/window_test_runner.h b/tests/cefclient/browser/window_test_runner.h
index 26a5324c..877fb59e 100644
--- a/tests/cefclient/browser/window_test_runner.h
+++ b/tests/cefclient/browser/window_test_runner.h
@@ -8,6 +8,8 @@
 
 #include "include/cef_browser.h"
 
+#include <optional>
+
 namespace client {
 namespace window_test {
 
@@ -15,6 +17,8 @@ namespace window_test {
 // the browser process UI thread unless otherwise indicated.
 class WindowTestRunner {
  public:
+  virtual ~WindowTestRunner() = default;
+
   virtual void SetPos(CefRefPtr<CefBrowser> browser,
                       int x,
                       int y,
@@ -28,7 +32,8 @@ class WindowTestRunner {
   // corner of the display.
   static void ModifyBounds(const CefRect& display, CefRect& window);
 
-  virtual ~WindowTestRunner() {}
+  virtual void SetTitleBarHeight(CefRefPtr<CefBrowser> browser,
+                                 const std::optional<float>& height);
 };
 
 }  // namespace window_test
diff --git a/tests/cefclient/browser/window_test_runner_views.cc b/tests/cefclient/browser/window_test_runner_views.cc
index 03aecf4d..9efda0ce 100644
--- a/tests/cefclient/browser/window_test_runner_views.cc
+++ b/tests/cefclient/browser/window_test_runner_views.cc
@@ -9,12 +9,15 @@
 #include "include/views/cef_window.h"
 #include "include/wrapper/cef_helpers.h"
 
+#include "tests/cefclient/browser/root_window_views.h"
+#include "tests/cefclient/browser/views_window.h"
+
 namespace client {
 namespace window_test {
 
 namespace {
 
-CefRefPtr<CefWindow> GetWindow(CefRefPtr<CefBrowser> browser) {
+CefRefPtr<CefWindow> GetWindow(const CefRefPtr<CefBrowser>& browser) {
   CEF_REQUIRE_UI_THREAD();
   DCHECK(browser->GetHost()->HasView());
 
@@ -27,6 +30,16 @@ CefRefPtr<CefWindow> GetWindow(CefRefPtr<CefBrowser> browser) {
   return window;
 }
 
+void SetTitlebarHeight(const CefRefPtr<CefBrowser>& browser,
+                       const std::optional<float>& height) {
+  CEF_REQUIRE_UI_THREAD();
+  auto root_window = RootWindow::GetForBrowser(browser->GetIdentifier());
+  DCHECK(root_window.get());
+
+  auto root_window_views = static_cast<RootWindowViews*>(root_window.get());
+  root_window_views->SetTitlebarHeight(height);
+}
+
 }  // namespace
 
 WindowTestRunnerViews::WindowTestRunnerViews() {}
@@ -56,5 +69,11 @@ void WindowTestRunnerViews::Restore(CefRefPtr<CefBrowser> browser) {
   GetWindow(browser)->Restore();
 }
 
+void WindowTestRunnerViews::SetTitleBarHeight(
+    CefRefPtr<CefBrowser> browser,
+    const std::optional<float>& height) {
+  SetTitlebarHeight(browser, height);
+}
+
 }  // namespace window_test
 }  // namespace client
diff --git a/tests/cefclient/browser/window_test_runner_views.h b/tests/cefclient/browser/window_test_runner_views.h
index 6bc66b0d..851e3742 100644
--- a/tests/cefclient/browser/window_test_runner_views.h
+++ b/tests/cefclient/browser/window_test_runner_views.h
@@ -24,6 +24,8 @@ class WindowTestRunnerViews : public WindowTestRunner {
   void Minimize(CefRefPtr<CefBrowser> browser) override;
   void Maximize(CefRefPtr<CefBrowser> browser) override;
   void Restore(CefRefPtr<CefBrowser> browser) override;
+  void SetTitleBarHeight(CefRefPtr<CefBrowser> browser,
+                         const std::optional<float>& height) override;
 };
 
 }  // namespace window_test
diff --git a/tests/cefclient/resources/window.html b/tests/cefclient/resources/window.html
index 7703d0d7..f01f7f52 100644
--- a/tests/cefclient/resources/window.html
+++ b/tests/cefclient/resources/window.html
@@ -1,4 +1,5 @@
-<html>
+<!DOCTYPE html>
+<html lang="en-US">
 <head>
 <title>Window Test</title>
 <script>
@@ -47,6 +48,14 @@ function position() {
   else
     send_message('Position', x + ',' + y + ',' + width + ',' + height);
 }
+
+function setTitlebarHeight() {
+  const height = parseFloat(document.getElementById('title_bar_height').value);
+  if (isNaN(height))
+    send_message('TitlebarHeight');
+  else
+    send_message('TitlebarHeight', height);
+}
 </script>
 </head>
 <body bgcolor="white" onload="setup()">
@@ -60,6 +69,8 @@ X: <input type="text" size="4" id="x" value="200">
 Y: <input type="text" size="4" id="y" value="100">
 Width: <input type="text" size="4" id="width" value="800">
 Height: <input type="text" size="4" id="height" value="600">
+<br/><input type="button" onclick="setTitlebarHeight();" value="Set Titlebar Height">
+<input type="number" min="0" max="100" id="title_bar_height" value="50"> (works on macOS with Views)
 </form>
 </body>
 </html>