Windows: Fix call of ToUnicode

ToUnicode sometimes gives wrong results if it is used with a
keyboard buffer containing the ctrl modifier. Special cases
containing alt and control might trigger the third assignment
of a key, but if no alt modifier is used for the key event,
we temporarily disable the control modifier in order to obtain
the character with ToUnicode.

Task-number: QTBUG-35734
Change-Id: Ifd88c640541b42fa65ee1dc9b55af3386714b0b8
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/src/plugins/platforms/windows/qwindowskeymapper.cpp b/src/plugins/platforms/windows/qwindowskeymapper.cpp
index ac9fe0878e..990dbaeba2 100644
--- a/src/plugins/platforms/windows/qwindowskeymapper.cpp
+++ b/src/plugins/platforms/windows/qwindowskeymapper.cpp
@@ -536,15 +536,16 @@ static inline int toKeyOrUnicode(int vk, int scancode, unsigned char *kbdBuffer,
     Q_ASSERT(vk > 0 && vk < 256);
     int code = 0;
     QChar unicodeBuffer[5];
-    int res = ToUnicode(vk, scancode, kbdBuffer, reinterpret_cast<LPWSTR>(unicodeBuffer), 5, 0);
-    // When Ctrl modifier is used ToUnicode does not return correct values. In order to assign the
-    // right key the control modifier is removed for just that function if the previous call failed.
-    if (res == 0 && kbdBuffer[VK_CONTROL]) {
-        const unsigned char controlState = kbdBuffer[VK_CONTROL];
+    // While key combinations containing alt and ctrl might trigger the third assignment of a key
+    // (for example "alt+ctrl+q" causes '@' on a German layout), ToUnicode often does not return the
+    // wanted character if only the ctrl modifier is used. Thus we unset this modifier temporarily
+    // if it is not used together with alt.
+    const unsigned char controlState = kbdBuffer[VK_MENU] ? 0 : kbdBuffer[VK_CONTROL];
+    if (controlState)
         kbdBuffer[VK_CONTROL] = 0;
-        res = ToUnicode(vk, scancode, kbdBuffer, reinterpret_cast<LPWSTR>(unicodeBuffer), 5, 0);
+    int res = ToUnicode(vk, scancode, kbdBuffer, reinterpret_cast<LPWSTR>(unicodeBuffer), 5, 0);
+    if (controlState)
         kbdBuffer[VK_CONTROL] = controlState;
-    }
     if (res)
         code = unicodeBuffer[0].toUpper().unicode();