Improve AltGr modifier triggering detection

A press/release of AltGr is translated by the system into the press/release of two keys - LCtrl and RAlt. In Far, for modifiers, activation is registered upon release, and the problem with AltGr is that, being a combined event, it triggered upon the release of the very first key in the combination - LCtrl, thereby producing "CtrlRAlt" instead of the expected "RAlt" (similarly for compound combinations).

This patch prevents premature reaction to the LCtrl release event.

Author: johnd0e

far/keyboard.cpp

@@ -101,7 +101,7 @@ enum MODIF_PRESSED_LAST
 	MODIF_CTRL  = 3_bit,
 	MODIF_RCTRL = 4_bit,
 };
-static bool LastWasDown;
+static bool LastWasDown, LastWasAltGr;
 
 static std::chrono::steady_clock::time_point KeyPressedLastTime;
 
@@ -1116,6 +1116,7 @@ static DWORD GetInputRecordImpl(INPUT_RECORD *rec,bool ExcludeMacro,bool Process
 	{
 		const auto CtrlState = rec->Event.KeyEvent.dwControlKeyState;
 		const auto KeyCode = rec->Event.KeyEvent.wVirtualKeyCode;
+		const auto KeyDown = rec->Event.KeyEvent.bKeyDown;
 
 		UpdateIntKeyState(CtrlState);
 
@@ -1127,10 +1128,15 @@ static DWORD GetInputRecordImpl(INPUT_RECORD *rec,bool ExcludeMacro,bool Process
 			true :
 			(CtrlState & SHIFT_PRESSED) != 0;
 
-		if (!rec->Event.KeyEvent.bKeyDown && CalcKey != KEY_NONE && !LastWasDown)
+		if (!KeyDown && CalcKey != KEY_NONE && !LastWasDown)
 			CalcKey = KEY_NONE;
 
-		LastWasDown = rec->Event.KeyEvent.bKeyDown;
+		if (LastWasAltGr && !KeyDown && KeyCode == VK_CONTROL && !(CtrlState & ENHANCED_KEY))
+			CalcKey = KEY_NONE;
+		else
+			LastWasDown = KeyDown;
+
+		LastWasAltGr = KeyCode==VK_MENU && ENHANCED_KEY == (CtrlState & (ENHANCED_KEY | LEFT_CTRL_PRESSED));
 
 		Panel::EndDrag();
 	}