Windows: Fix coordinate offset when positioning the taskbar on the left.

For windows that do not have WS_EX_TOOLWINDOW set, the WINDOWPLACEMENT
API uses workspace/available aera coordinates. Introduce a helper
function to return the offset and use that.

Task-number: QTBUG-43872
Change-Id: I329c640f180524699b45b855b4583f447c4a0987
Reviewed-by: Oliver Wolff <oliver.wolff@theqtcompany.com>

3 files changed, 40 insertions, 5 deletions

diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index fd57d9ee61..ae8020a53e 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -497,4 +497,13 @@ bool QWindowsScreenManager::handleScreenChanges()
     return true;
 }
 
+const QWindowsScreen *QWindowsScreenManager::screenAtDp(const QPoint &p) const
+{
+    foreach (QWindowsScreen *scr, m_screens) {
+        if (scr->geometryDp().contains(p))
+            return scr;
+    }
+    return Q_NULLPTR;
+}
+
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/windows/qwindowsscreen.h b/src/plugins/platforms/windows/qwindowsscreen.h
index aa1408358b..28256f3000 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.h
+++ b/src/plugins/platforms/windows/qwindowsscreen.h
@@ -137,6 +137,8 @@ public:
     bool handleDisplayChange(WPARAM wParam, LPARAM lParam);
     const WindowsScreenList &screens() const { return m_screens; }
 
+    const QWindowsScreen *screenAtDp(const QPoint &p) const;
+
 private:
     void removeScreen(int index);
 
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 1d8645f5f4..fbb61a1aff 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -169,6 +169,25 @@ QDebug operator<<(QDebug d, const NCCALCSIZE_PARAMS &p)
 }
 #endif // !Q_OS_WINCE
 
+// QTBUG-43872, for windows that do not have WS_EX_TOOLWINDOW set, WINDOWPLACEMENT
+// is in workspace/available area coordinates.
+static QPoint windowPlacementOffset(HWND hwnd, const QPoint &point)
+{
+#ifndef Q_OS_WINCE
+    if (GetWindowLongPtr(hwnd, GWL_EXSTYLE) & WS_EX_TOOLWINDOW)
+        return QPoint(0, 0);
+    const QWindowsScreenManager &screenManager = QWindowsContext::instance()->screenManager();
+    const QWindowsScreen *screen = screenManager.screens().size() == 1
+        ? screenManager.screens().first() : screenManager.screenAtDp(point);
+    if (screen)
+        return screen->availableGeometryDp().topLeft() - screen->geometryDp().topLeft();
+#else
+    Q_UNUSED(hwnd)
+    Q_UNUSED(point)
+#endif
+    return QPoint(0, 0);
+}
+
 // Return the frame geometry relative to the parent
 // if there is one.
 static inline QRect frameGeometry(HWND hwnd, bool topLevel)
@@ -179,8 +198,10 @@ static inline QRect frameGeometry(HWND hwnd, bool topLevel)
         WINDOWPLACEMENT windowPlacement;
         windowPlacement.length = sizeof(WINDOWPLACEMENT);
         GetWindowPlacement(hwnd, &windowPlacement);
-        if (windowPlacement.showCmd == SW_SHOWMINIMIZED)
-            return qrectFromRECT(windowPlacement.rcNormalPosition);
+        if (windowPlacement.showCmd == SW_SHOWMINIMIZED) {
+            const QRect result = qrectFromRECT(windowPlacement.rcNormalPosition);
+            return result.translated(windowPlacementOffset(hwnd, result.topLeft()));
+        }
     }
 #endif // !Q_OS_WINCE
     GetWindowRect(hwnd, &rect); // Screen coordinates.
@@ -1297,8 +1318,10 @@ static QRect normalFrameGeometry(HWND hwnd)
 #ifndef Q_OS_WINCE
     WINDOWPLACEMENT wp;
     wp.length = sizeof(WINDOWPLACEMENT);
-    if (GetWindowPlacement(hwnd, &wp))
-        return qrectFromRECT(wp.rcNormalPosition);
+    if (GetWindowPlacement(hwnd, &wp)) {
+        const QRect result = qrectFromRECT(wp.rcNormalPosition);
+        return result.translated(windowPlacementOffset(hwnd, result.topLeft()));
+    }
 #else
     Q_UNUSED(hwnd)
 #endif
@@ -1427,7 +1450,8 @@ void QWindowsWindow::setGeometry_sys(const QRect &rect) const
     // window, set the normal position of the window.
     if ((windowPlacement.showCmd == SW_MAXIMIZE && !IsWindowVisible(m_data.hwnd))
         || windowPlacement.showCmd == SW_SHOWMINIMIZED) {
-        windowPlacement.rcNormalPosition = RECTfromQRect(frameGeometry);
+        windowPlacement.rcNormalPosition =
+            RECTfromQRect(frameGeometry.translated(-windowPlacementOffset(m_data.hwnd, frameGeometry.topLeft())));
         windowPlacement.showCmd = windowPlacement.showCmd == SW_SHOWMINIMIZED ? SW_SHOWMINIMIZED : SW_HIDE;
         result = SetWindowPlacement(m_data.hwnd, &windowPlacement);
     } else