QStyleHelper: Base DPI-calculation on QScreen.

- Use qt_defaultDpiX() to obtain the resolution, which
  obtains it from QScreen. This implies that for X11,
  which previously used a hardcoded default of 96 DPI,
  the real resolution will be used (typically 75).

- Since many tests (layouts, graphicsview) contain
  test data for 96 DPI, add an attribute to
  QCoreApplication making it possible to set the
  resolution to 96 DPI for testing.

Change-Id: I77c8233a96b0d75de07406f58d48886a89c3de06
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

1 files changed, 3 insertions, 20 deletions

diff --git a/src/widgets/styles/qstylehelper.cpp b/src/widgets/styles/qstylehelper.cpp
index 823d29bc83..8f2d7364c1 100644
--- a/src/widgets/styles/qstylehelper.cpp
+++ b/src/widgets/styles/qstylehelper.cpp
@@ -46,17 +46,13 @@
 #include <private/qstyle_p.h>
 #include <qmath.h>
 
-#if defined(Q_WS_WIN)
-#include "qt_windows.h"
-#elif defined(Q_WS_MAC)
-#include <private/qt_cocoa_helpers_mac_p.h>
-#endif
-
 #include "qstylehelper_p.h"
 #include <qstringbuilder.h>
 
 QT_BEGIN_NAMESPACE
 
+Q_GUI_EXPORT int qt_defaultDpiX();
+
 namespace QStyleHelper {
 
 QString uniqueName(const QString &key, const QStyleOption *option, const QSize &size)
@@ -81,20 +77,7 @@ QString uniqueName(const QString &key, const QStyleOption *option, const QSize &
 
 qreal dpiScaled(qreal value)
 {
-    static qreal scale = -1;
-    if (scale < 0) {
-        scale = 1.0;
-#if defined(Q_WS_WIN)
-        {
-            HDC hdcScreen = GetDC(0);
-            int dpi = GetDeviceCaps(hdcScreen, LOGPIXELSX);
-            ReleaseDC(0, hdcScreen);
-            scale = dpi/96.0;
-        }
-#elif defined(Q_WS_MAC)
-    scale = qt_mac_get_scalefactor();
-#endif
-    }
+    static const qreal scale = qreal(qt_defaultDpiX()) / 96.0;
     return value * scale;
 }