Introduce FontSmoothingGamma as a platform style hint.

- Allocate gamma tables on the heap in a thread-safe way, use
  font smoothing returned by the style hints of the platform to
  calculate them.
- Improve font rendering on Windows.

Change-Id: I8cd39b51cf03cbd642474c02b9076814baecd597
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

3 files changed, 20 insertions, 12 deletions

diff --git a/src/plugins/platforms/windows/qwindowsfontdatabase.cpp b/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
index e0be731b53..7d0bd53e8b 100644
--- a/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
+++ b/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
@@ -68,8 +68,10 @@ QT_BEGIN_NAMESPACE
 */
 
 QWindowsFontEngineData::QWindowsFontEngineData()
+    : clearTypeEnabled(false)
+    , fontSmoothingGamma(QWindowsFontDatabase::fontSmoothingGamma())
 #if !defined(QT_NO_DIRECTWRITE)
-    : directWriteFactory(0)
+    , directWriteFactory(0)
     , directWriteGdiInterop(0)
 #endif
 {
@@ -78,17 +80,6 @@ QWindowsFontEngineData::QWindowsFontEngineData()
     if (SystemParametersInfo(SPI_GETFONTSMOOTHINGTYPE, 0, &result, 0))
         clearTypeEnabled = (result == FE_FONTSMOOTHINGCLEARTYPE);
 
-    int winSmooth;
-    if (SystemParametersInfo(0x200C /* SPI_GETFONTSMOOTHINGCONTRAST */, 0, &winSmooth, 0)) {
-        fontSmoothingGamma = winSmooth / qreal(1000.0);
-    } else {
-        fontSmoothingGamma = 1.0;
-    }
-
-    // Safeguard ourselves against corrupt registry values...
-    if (fontSmoothingGamma > 5 || fontSmoothingGamma < 1)
-        fontSmoothingGamma = qreal(1.4);
-
     const qreal gray_gamma = 2.31;
     for (int i=0; i<256; ++i)
         pow_gamma[i] = uint(qRound(qPow(i / qreal(255.), gray_gamma) * 2047));
@@ -110,6 +101,19 @@ QWindowsFontEngineData::~QWindowsFontEngineData()
 #endif
 }
 
+qreal QWindowsFontDatabase::fontSmoothingGamma()
+{
+    int winSmooth;
+    qreal result = 1;
+    if (SystemParametersInfo(0x200C /* SPI_GETFONTSMOOTHINGCONTRAST */, 0, &winSmooth, 0))
+        result = qreal(winSmooth) / qreal(1000.0);
+
+    // Safeguard ourselves against corrupt registry values...
+    if (result > 5 || result < 1)
+        result = qreal(1.4);
+    return result;
+}
+
 #if !defined(QT_NO_DIRECTWRITE)
 static inline bool initDirectWrite(QWindowsFontEngineData *d)
 {
diff --git a/src/plugins/platforms/windows/qwindowsfontdatabase.h b/src/plugins/platforms/windows/qwindowsfontdatabase.h
index f8f2a1eb85..774a203a55 100644
--- a/src/plugins/platforms/windows/qwindowsfontdatabase.h
+++ b/src/plugins/platforms/windows/qwindowsfontdatabase.h
@@ -96,6 +96,8 @@ public:
     static HFONT systemFont();
     static QFont LOGFONT_to_QFont(const LOGFONT& lf, int verticalDPI = 0);
 
+    static qreal fontSmoothingGamma();
+
 private:
     void populate(const QString &family = QString());
     QSharedPointer<QWindowsFontEngineData> m_fontEngineData;
diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index ee58a19ca9..fa63d77dd7 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -317,6 +317,8 @@ QVariant QWindowsIntegration::styleHint(QPlatformIntegration::StyleHint hint) co
     case QPlatformIntegration::KeyboardInputInterval:
     case QPlatformIntegration::ShowIsFullScreen:
         break; // Not implemented
+    case QPlatformIntegration::FontSmoothingGamma:
+        return QVariant(QWindowsFontDatabase::fontSmoothingGamma());
     }
     return QPlatformIntegration::styleHint(hint);
 }