WPF - Implement AltGr support. (#3131)

* Fixed #3104 AltGr support.

* Code format adjusted.

* Moved AltGr code to better location within the function.

Co-authored-by: Daniel Bitterlich <[email protected]>

Author: deonberlin

CefSharp.Core/Internals/CefBrowserHostWrapper.cpp

@@ -286,6 +286,7 @@ void CefBrowserHostWrapper::SendKeyEvent(int message, int wParam, int lParam)
     keyEvent.is_system_key = message == WM_SYSCHAR ||
         message == WM_SYSKEYDOWN ||
         message == WM_SYSKEYUP;
+    keyEvent.modifiers = GetCefKeyboardModifiers(wParam, lParam);
 
     if (message == WM_KEYDOWN || message == WM_SYSKEYDOWN)
     {
@@ -298,9 +299,29 @@ void CefBrowserHostWrapper::SendKeyEvent(int message, int wParam, int lParam)
     else
     {
         keyEvent.type = KEYEVENT_CHAR;
-    }
-    keyEvent.modifiers = GetCefKeyboardModifiers(wParam, lParam);
 
+        // mimic alt-gr check behaviour from
+        // src/ui/events/win/events_win_utils.cc: GetModifiersFromKeyState
+        if (IsKeyDown(VK_RMENU))
+        {
+            // reverse AltGr detection taken from PlatformKeyMap::UsesAltGraph
+            // instead of checking all combination for ctrl-alt, just check current char
+            HKL current_layout = ::GetKeyboardLayout(0);
+
+            // https://docs.microsoft.com/en-gb/windows/win32/api/winuser/nf-winuser-vkkeyscanexw
+            // ... high-order byte contains the shift state,
+            // which can be a combination of the following flag bits.
+            // 2 Either CTRL key is pressed.
+            // 4 Either ALT key is pressed.
+            SHORT scan_res = ::VkKeyScanExW(wParam, current_layout);
+            if (((scan_res >> 8) & 0xFF) == (2 | 4)) // ctrl-alt pressed
+            {
+                keyEvent.modifiers &= ~(EVENTFLAG_CONTROL_DOWN | EVENTFLAG_ALT_DOWN);
+                keyEvent.modifiers |= EVENTFLAG_ALTGR_DOWN;
+            }
+        }
+    }
+    
     _browserHost->SendKeyEvent(keyEvent);
 }