win: catch multimedia keys globally.

src/main.cpp

@@ -38,6 +38,51 @@
 #endif
 
 #ifdef Q_OS_WIN
+// code from patch attached to QTBUG-19064 by Honglei Zhang
+LRESULT QT_WIN_CALLBACK qt_LowLevelKeyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam);
+HHOOK hKeyboardHook;
+HINSTANCE hGuiLibInstance;
+
+LRESULT QT_WIN_CALLBACK qt_LowLevelKeyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam)
+{
+    LPKBDLLHOOKSTRUCT kbHookStruct = reinterpret_cast<LPKBDLLHOOKSTRUCT>(lParam);
+
+    switch(kbHookStruct->vkCode){
+    case VK_VOLUME_MUTE:
+    case VK_VOLUME_DOWN:
+    case VK_VOLUME_UP:
+    case VK_MEDIA_NEXT_TRACK:
+    case VK_MEDIA_PREV_TRACK:
+    case VK_MEDIA_STOP:
+    case VK_MEDIA_PLAY_PAUSE:
+    case VK_LAUNCH_MEDIA_SELECT:
+        // send message
+        {
+            HWND hWnd = NULL;
+            foreach (QWidget *widget, QApplication::topLevelWidgets()) {
+                // relay message to each top level widgets(window)
+                // if the window has focus, we don't send a duplicate message
+                if(QApplication::activeWindow() == widget){
+                    continue;
+                }
+
+                hWnd = widget->winId();
+
+                // generate message and post it to the message queue
+                LPKBDLLHOOKSTRUCT pKeyboardHookStruct = reinterpret_cast<LPKBDLLHOOKSTRUCT>(lParam);
+                WPARAM _wParam = pKeyboardHookStruct->vkCode;
+                LPARAM _lParam = MAKELPARAM(pKeyboardHookStruct->scanCode, pKeyboardHookStruct->flags);
+                PostMessage(hWnd, wParam, _wParam, _lParam);
+            }
+        }
+        break;
+    default:
+        break;
+    }
+
+    return CallNextHookEx(0, nCode, wParam, lParam);
+}
+
 #include <io.h>
 #define argc __argc
 #define argv __argv
@@ -46,6 +91,13 @@
 int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
     PSTR szCmdLine, int iCmdShow)
 {
+    hKeyboardHook = NULL;
+    hGuiLibInstance = hInstance;
+
+
+    // setup keyboard hook to receive multimedia key events when application is at background
+    hKeyboardHook = SetWindowsHookEx(WH_KEYBOARD_LL,(HOOKPROC) qt_LowLevelKeyboardHookProc, hGuiLibInstance, 0);
+
     if (fileno (stdout) != -1 && _get_osfhandle (fileno (stdout)) != -1)
     {
         /* stdout is fine, presumably redirected to a file or pipe */
@@ -126,7 +178,16 @@ main( int argc, char *argv[] )
         a.loadUrl( arg );
     }
 
-    return a.exec();
+    int returnCode = a.exec();
+#ifdef Q_OS_WIN
+    // clean up keyboard hook
+    if( hKeyboardHook )
+    {
+        UnhookWindowsHookEx(hKeyboardHook);
+        hKeyboardHook = NULL;
+    }
+#endif
+    return returnCode;
 }