Windows styles: Add device pixel scaling for system metrics.

Metrics obtained from the system must be scaled down
when device pixel ration scaling is in effect. Factor out
functions to return the device pixel values which might still
be used for drawing.

Task-number: QTBUG-38993
Task-number: QTBUG-38858
Change-Id: I6b90629e4979436bbb46f8c1fa1ee2253ada7ece
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>

1 files changed, 68 insertions, 71 deletions

diff --git a/src/widgets/styles/qwindowsstyle.cpp b/src/widgets/styles/qwindowsstyle.cpp
index cf0afd8031..44242177dc 100644
--- a/src/widgets/styles/qwindowsstyle.cpp
+++ b/src/widgets/styles/qwindowsstyle.cpp
@@ -118,6 +118,9 @@ enum QSliderDirection { SlUp, SlDown, SlLeft, SlRight };
 /*
     \internal
 */
+
+int QWindowsStylePrivate::m_appDevicePixelRatio = 0;
+
 QWindowsStylePrivate::QWindowsStylePrivate()
     : alt_down(false), menuBarTimer(0)
 {
@@ -130,6 +133,13 @@ QWindowsStylePrivate::QWindowsStylePrivate()
 #endif
 }
 
+int QWindowsStylePrivate::appDevicePixelRatio()
+{
+    if (!QWindowsStylePrivate::m_appDevicePixelRatio)
+        QWindowsStylePrivate::m_appDevicePixelRatio = qRound(qApp->devicePixelRatio());
+    return QWindowsStylePrivate::m_appDevicePixelRatio;
+}
+
 // Returns \c true if the toplevel parent of \a widget has seen the Alt-key
 bool QWindowsStylePrivate::hasSeenAlt(const QWidget *widget) const
 {
@@ -295,19 +305,76 @@ void QWindowsStyle::polish(QPalette &pal)
     QCommonStyle::polish(pal);
 }
 
+int QWindowsStylePrivate::pixelMetricFromSystemDp(QStyle::PixelMetric pm, const QStyleOption *, const QWidget *widget)
+{
+    switch (pm) {
+#if defined(Q_OS_WIN) && !defined(Q_OS_WINRT)
+    case QStyle::PM_DockWidgetFrameWidth:
+#  ifndef Q_OS_WINCE
+        return GetSystemMetrics(SM_CXFRAME);
+#  else
+        return GetSystemMetrics(SM_CXDLGFRAME);
+#  endif
+        break;
+
+    case QStyle::PM_TitleBarHeight:
+        if (widget && (widget->windowType() == Qt::Tool)) {
+            // MS always use one less than they say
+#  ifndef Q_OS_WINCE
+            return GetSystemMetrics(SM_CYSMCAPTION) - 1;
+#  else
+            return GetSystemMetrics(SM_CYCAPTION) - 1;
+#  endif
+        }
+        return GetSystemMetrics(SM_CYCAPTION) - 1;
+
+#  ifndef Q_OS_WINCE
+    case QStyle::PM_ScrollBarExtent:
+        {
+            NONCLIENTMETRICS ncm;
+            ncm.cbSize = FIELD_OFFSET(NONCLIENTMETRICS, lfMessageFont) + sizeof(LOGFONT);
+            if (SystemParametersInfo(SPI_GETNONCLIENTMETRICS, sizeof(NONCLIENTMETRICS), &ncm, 0))
+                return qMax(ncm.iScrollHeight, ncm.iScrollWidth);
+        }
+        break;
+#  endif // !Q_OS_WINCE
+
+    case  QStyle::PM_MdiSubWindowFrameWidth:
+#  ifndef Q_OS_WINCE
+        return GetSystemMetrics(SM_CYFRAME);
+#  else
+        return GetSystemMetrics(SM_CYDLGFRAME);
+#  endif
+#else
+    Q_UNUSED(widget)
+#endif // Q_OS_WIN
+
+    default:
+        break;
+    }
+    return QWindowsStylePrivate::InvalidMetric;
+}
+
 /*!
   \reimp
 */
 int QWindowsStyle::pixelMetric(PixelMetric pm, const QStyleOption *opt, const QWidget *widget) const
 {
-    int ret;
+    int ret = QWindowsStylePrivate::pixelMetricFromSystemDp(pm, opt, widget);
+    if (ret != QWindowsStylePrivate::InvalidMetric)
+        return ret / QWindowsStylePrivate::devicePixelRatio(widget);
+
+    ret = 0;
 
     switch (pm) {
+    case PM_ToolBarItemSpacing:
+        break;
     case PM_ButtonDefaultIndicator:
     case PM_ButtonShiftHorizontal:
     case PM_ButtonShiftVertical:
     case PM_MenuHMargin:
     case PM_MenuVMargin:
+    case PM_ToolBarItemMargin:
         ret = 1;
         break;
     case PM_DockWidgetSeparatorExtent:
@@ -315,7 +382,6 @@ int QWindowsStyle::pixelMetric(PixelMetric pm, const QStyleOption *opt, const QW
         break;
 #ifndef QT_NO_TABBAR
     case PM_TabBarTabShiftHorizontal:
-        ret = 0;
         break;
     case PM_TabBarTabShiftVertical:
         ret = 2;
@@ -357,23 +423,14 @@ int QWindowsStyle::pixelMetric(PixelMetric pm, const QStyleOption *opt, const QW
             if (space > 0)
                 thick += (space * 2) / (n + 2);
             ret = thick;
-        } else {
-            ret = 0;
         }
         break;
 #endif // QT_NO_SLIDER
 
 #ifndef QT_NO_MENU
     case PM_MenuBarHMargin:
-        ret = 0;
-        break;
-
     case PM_MenuBarVMargin:
-        ret = 0;
-        break;
-
     case PM_MenuBarPanelWidth:
-        ret = 0;
         break;
 
     case PM_SmallIconSize:
@@ -394,76 +451,16 @@ int QWindowsStyle::pixelMetric(PixelMetric pm, const QStyleOption *opt, const QW
     case PM_DockWidgetTitleBarButtonMargin:
         ret = int(QStyleHelper::dpiScaled(4.));
         break;
-#if defined(Q_WS_WIN)
-    case PM_DockWidgetFrameWidth:
-#if defined(Q_OS_WINCE)
-        ret = GetSystemMetrics(SM_CXDLGFRAME);
-#else
-        ret = GetSystemMetrics(SM_CXFRAME);
-#endif
-        break;
-#else
     case PM_DockWidgetFrameWidth:
         ret = 4;
         break;
-#endif // Q_WS_WIN
     break;
 
 #endif // QT_NO_MENU
-
-
-#if defined(Q_OS_WIN)
-#ifndef Q_OS_WINRT // There is no title bar in Windows Runtime applications
-    case PM_TitleBarHeight:
-        if (widget && (widget->windowType() == Qt::Tool)) {
-            // MS always use one less than they say
-#if defined(Q_OS_WINCE)
-            ret = GetSystemMetrics(SM_CYCAPTION) - 1;
-#else
-            ret = GetSystemMetrics(SM_CYSMCAPTION) - 1;
-#endif
-        } else {
-            ret = GetSystemMetrics(SM_CYCAPTION) - 1;
-        }
-
-        break;
-#endif // !Q_OS_WINRT
-
-    case PM_ScrollBarExtent:
-        {
-#if !defined(Q_OS_WINCE) && !defined(Q_OS_WINRT)
-            NONCLIENTMETRICS ncm;
-            ncm.cbSize = FIELD_OFFSET(NONCLIENTMETRICS, lfMessageFont) + sizeof(LOGFONT);
-            if (SystemParametersInfo(SPI_GETNONCLIENTMETRICS, sizeof(NONCLIENTMETRICS), &ncm, 0))
-                ret = qMax(ncm.iScrollHeight, ncm.iScrollWidth);
-            else
-#endif // !Q_OS_WINCE && !Q_OS_WINRT
-                ret = QCommonStyle::pixelMetric(pm, opt, widget);
-        }
-        break;
-#endif // Q_OS_WIN
-
     case PM_SplitterWidth:
         ret = qMax(4, QApplication::globalStrut().width());
         break;
 
-#if defined(Q_OS_WIN)
-#ifndef Q_OS_WINRT // Mdi concept not available for WinRT applications
-    case PM_MdiSubWindowFrameWidth:
-#if defined(Q_OS_WINCE)
-        ret = GetSystemMetrics(SM_CYDLGFRAME);
-#else
-        ret = GetSystemMetrics(SM_CYFRAME);
-#endif
-        break;
-#endif // !Q_OS_WINRT
-#endif // Q_OS_WIN
-    case PM_ToolBarItemMargin:
-        ret = 1;
-        break;
-    case PM_ToolBarItemSpacing:
-        ret = 0;
-        break;
     case PM_ToolBarHandleExtent:
         ret = int(QStyleHelper::dpiScaled(10.));
         break;