fix(windows): position child host windows in parent-client coordinates

flutter_inappwebview_windows/CHANGELOG.md

@@ -6,6 +6,9 @@
 - Updated Microsoft.Windows.ImplementationLibrary to `1.0.260126.7` and
   Microsoft.Web.WebView2 to `1.0.4078.44` for current MSVC toolchains.
 - Fixed internal WebView host windows stealing focus from the Flutter window.
+- Fixed owned popups (`<select>` dropdowns, print preview pickers, context
+  menus) opening away from the WebView after the host windows became
+  `WS_CHILD`: positioning now uses parent-client coordinates.
 - Added profile-scoped WebView2 preferred color-scheme control.
 - Updated flutter_inappwebview_platform_interface version to ^1.4.0-beta.3
 - Updated Microsoft.Web.WebView2 SDK version from `1.0.2849.39` to `1.0.3650.58`

flutter_inappwebview_windows/test/native_host_window_position_test.dart

@@ -0,0 +1,42 @@
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+
+/// The WebView host HWNDs are WS_CHILD of the Flutter window (see
+/// native_host_window_style_test.dart), so SetWindowPos takes parent-client
+/// coordinates. Positioning them with screen coordinates leaves every owned
+/// popup - <select> dropdowns, the print preview pickers, context menus -
+/// offset by the window origin.
+void main() {
+  final source =
+      File('windows/in_app_webview/in_app_webview.cpp')
+          .readAsStringSync()
+          .replaceAll('\r\n', '\n');
+  final setPosition = source.substring(
+    source.indexOf('void InAppWebView::setPosition('),
+    source.indexOf('void InAppWebView::setCursorPos('),
+  );
+
+  test('setPosition uses parent-client coordinates', () {
+    expect(setPosition, contains('SetWindowPos'));
+    expect(setPosition, contains('scaled_x,'));
+    expect(setPosition, contains('scaled_y,'));
+  });
+
+  test('setPosition does not reintroduce screen-coordinate math', () {
+    for (final banned in const [
+      'GetWindowRect',
+      'GetSystemMetrics',
+      'SM_CYCAPTION',
+      'SM_CXPADDEDBORDER',
+      'ClientToScreen',
+    ]) {
+      expect(
+        setPosition,
+        isNot(contains(banned)),
+        reason: '$banned belongs to screen-space positioning, which is wrong '
+            'for a WS_CHILD host window',
+      );
+    }
+  });
+}

flutter_inappwebview_windows/windows/in_app_webview/in_app_webview.cpp

@@ -3900,32 +3900,25 @@ namespace flutter_inappwebview_plugin
 
   void InAppWebView::setPosition(size_t x, size_t y, float scale_factor)
   {
-    if (!webViewController || !plugin || !plugin->registrar) {
+    if (!webViewController) {
       return;
     }
 
-    if (x >= 0 && y >= 0) {
-      scaleFactor_ = scale_factor;
-      auto scaled_x = static_cast<int>(x * scale_factor);
-      auto scaled_y = static_cast<int>(y * scale_factor);
-      widgetOffset_ = { scaled_x, scaled_y };
-
-      auto titleBarHeight = ((GetSystemMetrics(SM_CYCAPTION) + GetSystemMetrics(SM_CYFRAME)) * scale_factor) + GetSystemMetrics(SM_CXPADDEDBORDER);
-      auto borderWidth = (GetSystemMetrics(SM_CXBORDER) + GetSystemMetrics(SM_CXPADDEDBORDER)) * scale_factor;
-
-      RECT flutterWindowRect;
-      HWND flutterWindowHWnd = plugin->registrar->GetView()->GetNativeWindow();
-      GetWindowRect(flutterWindowHWnd, &flutterWindowRect);
-
-      HWND webViewHWnd;
-      if (succeededOrLog(webViewController->get_ParentWindow(&webViewHWnd))) {
-        ::SetWindowPos(webViewHWnd,
-          nullptr,
-          static_cast<int>(flutterWindowRect.left + scaled_x - borderWidth),
-          static_cast<int>(flutterWindowRect.top + scaled_y - titleBarHeight),
-          0, 0,
-          SWP_NOZORDER | SWP_NOSIZE | SWP_NOACTIVATE);
-      }
+    scaleFactor_ = scale_factor;
+    auto scaled_x = static_cast<int>(x * scale_factor);
+    auto scaled_y = static_cast<int>(y * scale_factor);
+    widgetOffset_ = { scaled_x, scaled_y };
+
+    HWND webViewHWnd;
+    if (succeededOrLog(webViewController->get_ParentWindow(&webViewHWnd))) {
+      // The host window is a WS_CHILD of the Flutter window, so SetWindowPos
+      // takes parent-client coordinates - exactly the widget offset.
+      ::SetWindowPos(webViewHWnd,
+        nullptr,
+        scaled_x,
+        scaled_y,
+        0, 0,
+        SWP_NOZORDER | SWP_NOSIZE | SWP_NOACTIVATE);
     }
   }