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>

src/corelib/global/qnamespace.h

@@ -479,8 +479,7 @@ public:
         AA_MacPluginApplication = 5,
         AA_DontUseNativeMenuBar = 6,
         AA_MacDontSwapCtrlAndMeta = 7,
-        AA_S60DontConstructApplicationPanes = 8,
-        AA_S60DisablePartialScreenInputMode = 9,
+        AA_Use96Dpi = 8,
         AA_X11InitThreads = 10,
 
         // Add new attributes before this line

src/gui/text/qfont.cpp

@@ -138,36 +138,32 @@ extern bool qt_is_gui_used;
 
 Q_GUI_EXPORT int qt_defaultDpiX()
 {
+    if (qApp->testAttribute(Qt::AA_Use96Dpi))
+        return 96;
+
     if (!qt_is_gui_used)
         return 75;
 
-    int dpi;
-    QScreen *screen = QGuiApplication::primaryScreen();
-    if (screen) {
-        dpi = qRound(screen->logicalDotsPerInchX());
-    } else {
-        //PI has not been initialised, or it is being initialised. Give a default dpi
-        dpi = 100;
-    }
+    if (const QScreen *screen = QGuiApplication::primaryScreen())
+        return qRound(screen->logicalDotsPerInchX());
 
-    return dpi;
+    //PI has not been initialised, or it is being initialised. Give a default dpi
+    return 100;
 }
 
 Q_GUI_EXPORT int qt_defaultDpiY()
 {
+    if (qApp->testAttribute(Qt::AA_Use96Dpi))
+        return 96;
+
     if (!qt_is_gui_used)
         return 75;
 
-    int dpi;
-    QScreen *screen = QGuiApplication::primaryScreen();
-    if (screen) {
-        dpi = qRound(screen->logicalDotsPerInchY());
-    } else {
-        //PI has not been initialised, or it is being initialised. Give a default dpi
-        dpi = 100;
-    }
+    if (const QScreen *screen = QGuiApplication::primaryScreen())
+        return qRound(screen->logicalDotsPerInchY());
 
-    return dpi;
+    //PI has not been initialised, or it is being initialised. Give a default dpi
+    return 100;
 }
 
 Q_GUI_EXPORT int qt_defaultDpi()

src/testlib/qtest.h

@@ -254,6 +254,7 @@ int main(int argc, char *argv[]) \
 int main(int argc, char *argv[]) \
 { \
     QApplication app(argc, argv); \
+    app.setAttribute(Qt::AA_Use96Dpi, true); \
     QTEST_DISABLE_KEYPAD_NAVIGATION \
     TestObject tc; \
     return QTest::qExec(&tc, argc, argv); \
@@ -267,6 +268,7 @@ int main(int argc, char *argv[]) \
 int main(int argc, char *argv[]) \
 { \
     QGuiApplication app(argc, argv); \
+    app.setAttribute(Qt::AA_Use96Dpi, true); \
     TestObject tc; \
     return QTest::qExec(&tc, argc, argv); \
 }
@@ -277,6 +279,7 @@ int main(int argc, char *argv[]) \
 int main(int argc, char *argv[]) \
 { \
     QCoreApplication app(argc, argv); \
+    app.setAttribute(Qt::AA_Use96Dpi, true); \
     TestObject tc; \
     return QTest::qExec(&tc, argc, argv); \
 }
@@ -287,6 +290,7 @@ int main(int argc, char *argv[]) \
 int main(int argc, char *argv[]) \
 { \
     QCoreApplication app(argc, argv); \
+    app.setAttribute(Qt::AA_Use96Dpi, true); \
     TestObject tc; \
     return QTest::qExec(&tc, argc, argv); \
 }

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;
 }