Add window centering functionality to all platforms

Introduces a new Center() method to the Window class and exposes it via the C API. Implements platform-specific logic to center the window on the screen for Windows, macOS, Linux, and iOS. On Android and OpenHarmony, centering is not supported and is stubbed with warnings or no-ops.

Author: lijy91

src/capi/window_c.cpp

@@ -381,6 +381,14 @@ native_point_t native_window_get_position(native_window_t window) {
   return result;
 }
 
+FFI_PLUGIN_EXPORT
+void native_window_center(native_window_t window) {
+  if (!window)
+    return;
+  auto* win = static_cast<nativeapi::Window*>(window);
+  win->Center();
+}
+
 // Window properties
 FFI_PLUGIN_EXPORT
 void native_window_set_resizable(native_window_t window, bool resizable) {

src/capi/window_c.h

@@ -163,6 +163,9 @@ void native_window_set_position(native_window_t window, double x, double y);
 FFI_PLUGIN_EXPORT
 native_point_t native_window_get_position(native_window_t window);
 
+FFI_PLUGIN_EXPORT
+void native_window_center(native_window_t window);
+
 // Window properties
 FFI_PLUGIN_EXPORT
 void native_window_set_resizable(native_window_t window, bool resizable);

src/platform/android/window_android.cpp

@@ -278,6 +278,12 @@ Point Window::GetPosition() const {
   return Point{0, 0};
 }
 
+void Window::Center() {
+  // On Android, window positioning is not supported
+  // Activities are automatically managed by the system
+  ALOGW("Center not supported on Android - Activities are managed by the system");
+}
+
 void Window::SetTitle(std::string title) {
   ALOGW("SetTitle not supported on Android (use Activity title)");
 }

src/platform/ios/window_ios.mm

@@ -288,6 +288,27 @@
   return Point{static_cast<double>(origin.x), static_cast<double>(origin.y)};
 }
 
+void Window::Center() {
+  if (!pimpl_->ui_window_)
+    return;
+
+  // Get the screen bounds
+  UIScreen* screen = pimpl_->ui_window_.screen ?: [UIScreen mainScreen];
+  CGRect screenBounds = screen.bounds;
+
+  // Get the current window size
+  CGRect windowFrame = pimpl_->ui_window_.frame;
+
+  // Calculate center position
+  CGFloat centerX = (screenBounds.size.width - windowFrame.size.width) / 2.0;
+  CGFloat centerY = (screenBounds.size.height - windowFrame.size.height) / 2.0;
+
+  // Set the centered frame
+  windowFrame.origin.x = centerX;
+  windowFrame.origin.y = centerY;
+  pimpl_->ui_window_.frame = windowFrame;
+}
+
 void Window::SetTitle(std::string title) {
   // iOS windows don't have titles (use view controller title)
   if (pimpl_->ui_window_) {

src/platform/linux/window_linux.cpp

@@ -314,6 +314,35 @@ Point Window::GetPosition() const {
   return point;
 }
 
+void Window::Center() {
+  if (!pimpl_->gdk_window_)
+    return;
+
+  // Get the window size
+  gint window_width, window_height;
+  gdk_window_get_geometry(pimpl_->gdk_window_, nullptr, nullptr, &window_width, &window_height);
+
+  // Get the screen size
+  GdkDisplay* display = gdk_window_get_display(pimpl_->gdk_window_);
+  GdkMonitor* monitor = gdk_display_get_primary_monitor(display);
+  if (!monitor) {
+    // Fallback to first monitor if no primary monitor is found
+    monitor = gdk_display_get_monitor(display, 0);
+  }
+
+  if (monitor) {
+    GdkRectangle geometry;
+    gdk_monitor_get_geometry(monitor, &geometry);
+
+    // Calculate center position
+    gint center_x = geometry.x + (geometry.width - window_width) / 2;
+    gint center_y = geometry.y + (geometry.height - window_height) / 2;
+
+    // Move the window to center
+    gdk_window_move(pimpl_->gdk_window_, center_x, center_y);
+  }
+}
+
 void Window::SetTitle(std::string title) {
   // GDK windows don't have titles directly - this would be set on the GTK
   // widget For now, provide stub implementation

src/platform/macos/window_macos.mm

@@ -283,6 +283,14 @@
   return point;
 }
 
+void Window::Center() {
+  if (!pimpl_->ns_window_)
+    return;
+
+  // Use NSWindow's center method which automatically centers on the main screen
+  [pimpl_->ns_window_ center];
+}
+
 void Window::SetTitle(std::string title) {
   [pimpl_->ns_window_ setTitle:[NSString stringWithUTF8String:title.c_str()]];
 }

src/platform/ohos/window_ohos.cpp

@@ -260,6 +260,14 @@ Point Window::GetPosition() const {
   return Point{0, 0};
 }
 
+void Window::Center() {
+  // On OpenHarmony, window positioning is not supported
+  // Abilities are automatically managed by the system
+  if (pimpl_->native_window_) {
+    // Center not supported on OpenHarmony - Abilities are managed by the system
+  }
+}
+
 void Window::SetTitle(std::string title) {
   // SetTitle not supported on OpenHarmony (use Ability title)
 }

src/platform/windows/window_windows.cpp

@@ -436,6 +436,30 @@ Point Window::GetPosition() const {
   return point;
 }
 
+void Window::Center() {
+  if (!pimpl_->hwnd_)
+    return;
+
+  // Get the current window size
+  RECT windowRect;
+  GetWindowRect(pimpl_->hwnd_, &windowRect);
+  int windowWidth = windowRect.right - windowRect.left;
+  int windowHeight = windowRect.bottom - windowRect.top;
+
+  // Get the monitor that the window is currently on
+  HMONITOR monitor = MonitorFromWindow(pimpl_->hwnd_, MONITOR_DEFAULTTONEAREST);
+  MONITORINFO mi = {sizeof(mi)};
+  GetMonitorInfo(monitor, &mi);
+
+  // Calculate the center position on the monitor's work area
+  int centerX = mi.rcWork.left + (mi.rcWork.right - mi.rcWork.left - windowWidth) / 2;
+  int centerY = mi.rcWork.top + (mi.rcWork.bottom - mi.rcWork.top - windowHeight) / 2;
+
+  // Set the window position to center
+  SetWindowPos(pimpl_->hwnd_, nullptr, centerX, centerY, 0, 0,
+               SWP_NOSIZE | SWP_NOZORDER | SWP_NOACTIVATE);
+}
+
 void Window::SetTitle(std::string title) {
   if (pimpl_->hwnd_) {
     std::wstring wtitle = StringToWString(title);

src/window.h

@@ -462,6 +462,15 @@ class Window : public NativeObjectProvider {
    */
   Point GetPosition() const;
 
+  /**
+   * @brief Centers the window on the screen.
+   *
+   * Moves the window to the center of the primary display. The window
+   * will be positioned so that its center point aligns with the center
+   * of the screen.
+   */
+  void Center();
+
   /**
    * @brief Sets the text displayed in the window's title bar.
    *