From be4d1ef0382216640102522b6914989aac99623c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dariusz=20Komosi=C5=84ski?= <darek.komosinski@gmail.com>
Date: Tue, 3 Dec 2019 16:37:22 +0100
Subject: [PATCH] Fix right ALT and CTRL being reported as left.

---
 src/Avalonia.Input/AccessKeyHandler.cs        |  3 ++-
 .../Avalonia.Win32/Input/KeyInterop.cs        | 21 ++++++++++++++++---
 src/Windows/Avalonia.Win32/WindowImpl.cs      |  4 ++--
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/Avalonia.Input/AccessKeyHandler.cs b/src/Avalonia.Input/AccessKeyHandler.cs
index aa009770f6..00e68d629b 100644
--- a/src/Avalonia.Input/AccessKeyHandler.cs
+++ b/src/Avalonia.Input/AccessKeyHandler.cs
@@ -140,7 +140,7 @@ namespace Avalonia.Input
         /// <param name="e">The event args.</param>
         protected virtual void OnPreviewKeyDown(object sender, KeyEventArgs e)
         {
-            if (e.Key == Key.LeftAlt)
+            if (e.Key == Key.LeftAlt || e.Key == Key.RightAlt)
             {
                 _altIsDown = true;
 
@@ -218,6 +218,7 @@ namespace Avalonia.Input
             switch (e.Key)
             {
                 case Key.LeftAlt:
+                case Key.RightAlt:
                     _altIsDown = false;
 
                     if (_ignoreAltUp)
diff --git a/src/Windows/Avalonia.Win32/Input/KeyInterop.cs b/src/Windows/Avalonia.Win32/Input/KeyInterop.cs
index 11c0a6dca9..acb4f52d88 100644
--- a/src/Windows/Avalonia.Win32/Input/KeyInterop.cs
+++ b/src/Windows/Avalonia.Win32/Input/KeyInterop.cs
@@ -364,10 +364,25 @@ namespace Avalonia.Win32.Input
             { 254, Key.OemClear },
         };
 
-        public static Key KeyFromVirtualKey(int virtualKey)
+        public static Key KeyFromVirtualKey(int virtualKey, int flags)
         {
-            Key result;
-            s_keyFromVirtualKey.TryGetValue(virtualKey, out result);
+            s_keyFromVirtualKey.TryGetValue(virtualKey, out var result);
+
+            // Indicates whether the key is an extended key, such as the right-hand ALT and CTRL keys.
+            // According to https://docs.microsoft.com/en-us/windows/win32/inputdev/wm-keydown.
+            const int extendedMask = 1 << 24;
+            bool isExtended = (flags & extendedMask) != 0;
+
+            if (isExtended)
+            {
+                return result switch
+                {
+                    Key.LeftAlt => Key.RightAlt,
+                    Key.LeftCtrl => Key.RightCtrl,
+                    _ => result
+                };
+            }
+
             return result;
         }
 
diff --git a/src/Windows/Avalonia.Win32/WindowImpl.cs b/src/Windows/Avalonia.Win32/WindowImpl.cs
index 66c2432472..9a929bcfb5 100644
--- a/src/Windows/Avalonia.Win32/WindowImpl.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.cs
@@ -516,7 +516,7 @@ namespace Avalonia.Win32
                             timestamp,
                             _owner,
                             RawKeyEventType.KeyDown,
-                            KeyInterop.KeyFromVirtualKey(ToInt32(wParam)), WindowsKeyboardDevice.Instance.Modifiers);
+                            KeyInterop.KeyFromVirtualKey(ToInt32(wParam), ToInt32(lParam)), WindowsKeyboardDevice.Instance.Modifiers);
                     break;
 
                 case UnmanagedMethods.WindowsMessage.WM_MENUCHAR:
@@ -530,7 +530,7 @@ namespace Avalonia.Win32
                             timestamp,
                             _owner,
                             RawKeyEventType.KeyUp,
-                            KeyInterop.KeyFromVirtualKey(ToInt32(wParam)), WindowsKeyboardDevice.Instance.Modifiers);
+                            KeyInterop.KeyFromVirtualKey(ToInt32(wParam), ToInt32(lParam)), WindowsKeyboardDevice.Instance.Modifiers);
                     break;
                 case UnmanagedMethods.WindowsMessage.WM_CHAR:
                     // Ignore control chars