QtPlatformHeaders/Windows: Add function to set window activation behavior.

The Windows OS by default does not activate windows when the calling
process is not active; only the taskbar entry is flashed as not to
distract the user.
Nevertheless, for some use cases, it is desirable to activate the window
also in the inactive state.
Introduce an enumeration specifying the behavior to QtPlatformHeaders
and employ a workaround using the Win32 API AttachThreadInput() to attach
to other processes while setting the foreground window to achieve
the AlwaysActivateWindow behavior.

Task-number: QTBUG-14062
Task-number: QTBUG-37435
Change-Id: I79cb6cd3fab29d55b5d3db7f9af01bbaa5096a37
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

src/gui/doc/qtgui.qdocconf

@@ -33,6 +33,7 @@ depends += \
     qtmultimedia \
     qtnetwork \
     qtopengl \
+    qtplatformheaders \
     qtsvg \
     qtqml \
     qtquick \

src/gui/kernel/qwindow.cpp

@@ -1002,7 +1002,7 @@ QRegion QWindow::mask() const
 /*!
     Requests the window to be activated, i.e. receive keyboard focus.
 
-    \sa isActive(), QGuiApplication::focusWindow()
+    \sa isActive(), QGuiApplication::focusWindow(), QWindowsWindowFunctions::setWindowActivationBehavior()
 */
 void QWindow::requestActivate()
 {

src/platformheaders/doc/qtplatformheaders.qdocconf

@@ -27,6 +27,7 @@ qhp.QtPlatformHeaders.subprojects.classes.sortPages = true
 depends += \
     qtcore \
     qtgui \
+    qtwidgets \
     qtdoc
 
 headerdirs  += ..

src/platformheaders/windowsfunctions/qwindowswindowfunctions.h

@@ -57,6 +57,11 @@ public:
 
     Q_DECLARE_FLAGS(TouchWindowTouchTypes, TouchWindowTouchType)
 
+    enum WindowActivationBehavior {
+        DefaultActivateWindow,
+        AlwaysActivateWindow
+    };
+
     typedef void (*SetTouchWindowTouchType)(QWindow *window, QWindowsWindowFunctions::TouchWindowTouchTypes touchType);
     static const QByteArray setTouchWindowTouchTypeIdentifier() { return QByteArrayLiteral("WindowsSetTouchWindowTouchType"); }
 
@@ -75,6 +80,16 @@ public:
         if (func)
             func(window, border);
     }
+
+    typedef void (*SetWindowActivationBehaviorType)(WindowActivationBehavior);
+    static const QByteArray setWindowActivationBehaviorIdentifier() { return QByteArrayLiteral("WindowsSetWindowActivationBehavior"); }
+
+    static void setWindowActivationBehavior(WindowActivationBehavior behavior)
+    {
+        SetWindowActivationBehaviorType func = reinterpret_cast<SetWindowActivationBehaviorType>(QGuiApplication::platformFunction(setWindowActivationBehaviorIdentifier()));
+        if (func)
+            func(behavior);
+    }
 };
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QWindowsWindowFunctions::TouchWindowTouchTypes)

src/platformheaders/windowsfunctions/qwindowswindowfunctions.qdoc

@@ -95,3 +95,52 @@
 
     See also \l [QtDoc] {Fullscreen OpenGL Based Windows}
 */
+
+/*!
+    \enum QWindowsWindowFunctions::WindowActivationBehavior
+
+    This enum specifies the behavior of QWidget::activateWindow() and
+    QWindow::requestActivate().
+
+    \value DefaultActivateWindow The window is activated according to the default
+        behavior of the Windows operating system. This means the window will not
+        be activated in some circumstances (most notably when the calling process
+        is not the active process); only the taskbar entry will be flashed.
+    \value AlwaysActivateWindow  The window is always activated, even when the
+        calling process is not the active process.
+
+    \sa QWidget::activateWindow(), QWindow::requestActivate()
+    \since 5.7
+*/
+
+/*!
+    \typedef QWindowsWindowFunctions::SetWindowActivationBehaviorType
+
+    This is the typedef for the function returned by QGuiApplication::platformFunction()
+    when passed setWindowActivationBehaviorIdentifier().
+
+    \sa QWidget::activateWindow(), QWindow::requestActivate()
+    \since 5.7
+*/
+
+/*!
+    \fn QByteArray setWindowActivationBehaviorIdentifier()
+
+    This function returns a bytearray that can be used to query
+    QGuiApplication::platformFunction() to retrieve the SetWindowActivationBehaviorType
+    function.
+
+    \sa QWidget::activateWindow(), QWindow::requestActivate()
+    \since 5.7
+*/
+
+/*!
+    \fn void QWindowsWindowFunctions::setWindowActivationBehavior(WindowActivationBehavior behavior)
+
+    This is a convenience function that can be used directly instead of resolving
+    the function pointer. \a behavior will be relayed to the function retrieved
+    by QGuiApplication.
+
+    \sa QWidget::activateWindow(), QWindow::requestActivate()
+    \since 5.7
+*/

src/plugins/platforms/windows/qwindowsnativeinterface.cpp

@@ -84,6 +84,9 @@ static int resourceType(const QByteArray &key)
     return int(result - names);
 }
 
+QWindowsWindowFunctions::WindowActivationBehavior QWindowsNativeInterface::m_windowActivationBehavior =
+    QWindowsWindowFunctions::DefaultActivateWindow;
+
 void *QWindowsNativeInterface::nativeResourceForWindow(const QByteArray &resource, QWindow *window)
 {
     if (!window || !window->handle()) {
@@ -253,6 +256,8 @@ QFunctionPointer QWindowsNativeInterface::platformFunction(const QByteArray &fun
         return QFunctionPointer(QWindowsWindow::setTouchWindowTouchTypeStatic);
     else if (function == QWindowsWindowFunctions::setHasBorderInFullScreenIdentifier())
         return QFunctionPointer(QWindowsWindow::setHasBorderInFullScreenStatic);
+    else if (function == QWindowsWindowFunctions::setWindowActivationBehaviorIdentifier())
+        return QFunctionPointer(QWindowsNativeInterface::setWindowActivationBehavior);
     return Q_NULLPTR;
 }
 

src/plugins/platforms/windows/qwindowsnativeinterface.h

@@ -42,6 +42,7 @@
 
 #include <QtGui/qfont.h>
 #include <QtGui/qpa/qplatformnativeinterface.h>
+#include <QtPlatformHeaders/qwindowswindowfunctions.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -96,7 +97,15 @@ public:
     QVariant windowProperty(QPlatformWindow *window, const QString &name, const QVariant &defaultValue) const Q_DECL_OVERRIDE;
     void setWindowProperty(QPlatformWindow *window, const QString &name, const QVariant &value) Q_DECL_OVERRIDE;
 
+    static QWindowsWindowFunctions::WindowActivationBehavior windowActivationBehavior()
+        { return QWindowsNativeInterface::m_windowActivationBehavior; }
+    static void setWindowActivationBehavior(QWindowsWindowFunctions::WindowActivationBehavior b)
+        { QWindowsNativeInterface::m_windowActivationBehavior = b; }
+
     QFunctionPointer platformFunction(const QByteArray &function) const Q_DECL_OVERRIDE;
+
+private:
+    static QWindowsWindowFunctions::WindowActivationBehavior m_windowActivationBehavior;
 };
 
 QT_END_NAMESPACE

src/plugins/platforms/windows/qwindowswindow.cpp

@@ -43,6 +43,7 @@
 #include "qwindowsdrag.h"
 #include "qwindowsscreen.h"
 #include "qwindowsintegration.h"
+#include "qwindowsnativeinterface.h"
 #include "qwindowsopenglcontext.h"
 #ifdef QT_NO_CURSOR
 #  include "qwindowscursor.h"
@@ -2083,8 +2084,30 @@ void QWindowsWindow::requestActivateWindow()
     // 'Active' state handling is based in focus since it needs to work for
     // child windows as well.
     if (m_data.hwnd) {
+#ifndef Q_OS_WINCE
+        const DWORD currentThread = GetCurrentThreadId();
+        bool attached = false;
+        DWORD foregroundThread = 0;
+
+        // QTBUG-14062, QTBUG-37435: Windows normally only flashes the taskbar entry
+        // when activating windows of inactive applications. Attach to the input of the
+        // currently active window while setting the foreground window to always activate
+        // the window when desired.
+        if (QGuiApplication::applicationState() != Qt::ApplicationActive
+            && QWindowsNativeInterface::windowActivationBehavior() == QWindowsWindowFunctions::AlwaysActivateWindow) {
+            if (const HWND foregroundWindow = GetForegroundWindow()) {
+                foregroundThread = GetWindowThreadProcessId(foregroundWindow, NULL);
+                if (foregroundThread && foregroundThread != currentThread)
+                    attached = AttachThreadInput(foregroundThread, currentThread, TRUE) == TRUE;
+            }
+        }
+#endif // !Q_OS_WINCE
         SetForegroundWindow(m_data.hwnd);
         SetFocus(m_data.hwnd);
+#ifndef Q_OS_WINCE
+        if (attached)
+            AttachThreadInput(foregroundThread, currentThread, FALSE);
+#endif // !Q_OS_WINCE
     }
 }
 

src/widgets/doc/qtwidgets.qdocconf

@@ -26,7 +26,7 @@ qhp.QtWidgets.subprojects.classes.sortPages = true
 
 tagfile                 = ../../../doc/qtwidgets/qtwidgets.tags
 
-depends                 += qtcore qtgui qtdoc qtsql qtdesigner qtquick qmake qtsvg
+depends                 += qtcore qtgui qtdoc qtsql qtdesigner qtquick qmake qtplatformheaders qtsvg
 
 headerdirs  += ..
 

src/widgets/kernel/qwidget.cpp

@@ -12689,7 +12689,7 @@ QWidget *QWidget::keyboardGrabber()
     does not allow an application to interrupt what the user is currently
     doing in another application.
 
-    \sa isActiveWindow(), window(), show()
+    \sa isActiveWindow(), window(), show(), QWindowsWindowFunctions::setWindowActivationBehavior()
 */
 void QWidget::activateWindow()
 {