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Re: AltGr key mostly fires an additional CONTROL key


On 15/08/2011 13:53, Oliver Schmidt wrote:
I also had problems with the AltGr key. These could reliably
be reproduced by holding the AltGr for some seconds (causing
Windows generating auto repeat events).

Unfortunately the test version at

ftp://cygwin.com/pub/cygwinx/XWin.20110801-git-2d9f9305cb559907.exe.bz2

doesn't fix this problem for me.

I discovered that the mechanism in winkeybd.c function
winIsFakeCtrl_L had a problem if PeekMessage cannot obtain
the next Alt_R message because it is not there.

I prepared a patch that remembers the last Ctrl_L event and
reacts on a later following Alt_R. It was also necessary to
alter the order in winWindowProc in winwndproc.c: the invocation
of winIsFakeCtrl_L had to be done before discarding auto-repeated
key presses.

The attached patch is against the sources of xserver-cygwin-1.10.3-1.

Thanks for the patch. The approach of remembering if the last keyevent was a Ctrl-L and reversing it if it was fake because it's followed by a AltGr is a good one, which hadn't occurred to me, and it clearly better than assuming the AltGr keyevent message will be available some fixed time after the Ctrl-L one.


(I had considered buffering the Ctrl-L keyevent until we could determine a AltGr wasn't going to be coming after it, but that would be more complex to implement)

A few comments on the patch follow. It could also do with some better comments, as what this code is trying to do is slightly obscure, and I assume that the old comments about TweakUI being the cause of this are just wrong (as you don't mention that you have it installed)

diff --git a/hw/xwin/winkeybd.c b/hw/xwin/winkeybd.c
index e807fc5..460c9d6 100644
--- a/hw/xwin/winkeybd.c
+++ b/hw/xwin/winkeybd.c
@@ -356,6 +356,12 @@ winIsFakeCtrl_L (UINT message, WPARAM wParam, LPARAM lParam)
   MSG		msgNext;
   LONG		lTime;
   Bool		fReturn;
+
+  static Bool   hasLastControlL = FALSE;
+  static UINT   lastMessage;
+  static WPARAM lastWparam;
+  static LPARAM lastLparam;
+  static LONG   lastTime;

I was going to suggest using static MSG lastMsg, but then I noticed that lastWparam, lastLparam are completely unused...


   /*
    * Fake Ctrl_L presses will be followed by an Alt_R keypress
@@ -389,9 +395,22 @@ winIsFakeCtrl_L (UINT message, WPARAM wParam, LPARAM lParam)
 				 WM_KEYDOWN, WM_SYSKEYDOWN,
 				 PM_NOREMOVE);
 	}
-      if (msgNext.message != WM_KEYDOWN && msgNext.message != WM_SYSKEYDOWN)
+      if (fReturn && msgNext.message != WM_KEYDOWN && msgNext.message != WM_SYSKEYDOWN)
           fReturn = 0;
+      if (!fReturn)
+        {
+          hasLastControlL = TRUE;
+          lastMessage = message;
+          lastWparam  = wParam;
+          lastLparam  = lParam;
+          lastTime    = lTime;
+        }
+      else
+        {
+          hasLastControlL = FALSE;
+        }
+
       /* Is next press an Alt_R with the same timestamp? */
       if (fReturn && msgNext.wParam == VK_MENU
 	  && msgNext.time == lTime
@@ -406,11 +425,33 @@ winIsFakeCtrl_L (UINT message, WPARAM wParam, LPARAM lParam)
 	}
     }

+  /*
+   * Check for Alt_R keypress, that was not ready when the
+   * last Ctrl_L appeared.
+   */
+  else if ((message == WM_KEYDOWN || message == WM_SYSKEYDOWN)
+      && wParam == VK_MENU
+      && (HIWORD (lParam) & KF_EXTENDED))
+    {
+      if (hasLastControlL)
+        {
+          lTime = GetMessageTime ();
+
+          if ((lastMessage == WM_KEYDOWN || lastMessage == WM_SYSKEYDOWN)
+              && lastTime == lTime)

Why is it necessary to check that the last message was WM_(SYS)KEYDOWN here? hasLastControlL can't get set unless it was?


+            {
+                /* take back the fake ctrl_L key */
+                winSendKeyEvent (KEY_LCtrl, FALSE);
+            }
+          hasLastControlL = FALSE;
+        }
+    }
+
   /*
    * Fake Ctrl_L releases will be followed by an Alt_R release
    * with the same timestamp as the Ctrl_L release.
    */
-  if ((message == WM_KEYUP || message == WM_SYSKEYUP)
+  else if ((message == WM_KEYUP || message == WM_SYSKEYUP)
       && wParam == VK_CONTROL
       && (HIWORD (lParam) & KF_EXTENDED) == 0)
     {
@@ -439,9 +480,11 @@ winIsFakeCtrl_L (UINT message, WPARAM wParam, LPARAM lParam)
 				 PM_NOREMOVE);
 	}

-      if (msgNext.message != WM_KEYUP && msgNext.message != WM_SYSKEYUP)
+      if (fReturn && msgNext.message != WM_KEYUP && msgNext.message != WM_SYSKEYUP)
           fReturn = 0;

+    hasLastControlL = FALSE;
+
       /* Is next press an Alt_R with the same timestamp? */
       if (fReturn
 	  && (msgNext.message == WM_KEYUP
@@ -458,6 +501,10 @@ winIsFakeCtrl_L (UINT message, WPARAM wParam, LPARAM lParam)
 	  return TRUE;
 	}
     }
+  else
+    {
+      hasLastControlL = FALSE;
+    }

   /* Not a fake control left press/release */
   return FALSE;
diff --git a/hw/xwin/winwndproc.c b/hw/xwin/winwndproc.c
index 316cf08..7de5a5d 100644
--- a/hw/xwin/winwndproc.c
+++ b/hw/xwin/winwndproc.c
@@ -1060,6 +1060,10 @@ winWindowProc (HWND hwnd, UINT message,
       if ((wParam == VK_LWIN || wParam == VK_RWIN) && !g_fKeyboardHookLL)
 	break;

+      /* Discard fake Ctrl_L presses that precede AltGR on non-US keyboards */
+      if (winIsFakeCtrl_L (message, wParam, lParam))
+	return 0;
+
       /*
        * Discard presses generated from Windows auto-repeat
        */
@@ -1080,10 +1084,6 @@ winWindowProc (HWND hwnd, UINT message,
         }
       }

-      /* Discard fake Ctrl_L presses that precede AltGR on non-US keyboards */
-      if (winIsFakeCtrl_L (message, wParam, lParam))
-	return 0;
-

Can you say why it's necessary to change the order here and why this is the correct ordering? A comment here might be a good idea :-)


       /* Translate Windows key code to X scan code */
       winTranslateKey (wParam, lParam, &iScanCode);



-- Jon TURNEY Volunteer Cygwin/X X Server maintainer

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