Enable gamma-correction on a face-by-face basis

Changes how we control if gamma-correction is done, and enables it for
the freetype CFF engine when stem-darkening is available.

The new code replaces existing hacks to force gamma-correction off
when using Freetype on X11 and Windows.

Change-Id: Ic703ca6965a3d81b204349e10f406c991b292edd
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

4 files changed, 38 insertions, 6 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 0b2972f189..8d8ca1ba2c 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -445,6 +445,11 @@ bool QFontEngine::supportsTransformation(const QTransform &transform) const
     return transform.type() < QTransform::TxProject;
 }
 
+bool QFontEngine::expectsGammaCorrectedBlending() const
+{
+    return true;
+}
+
 void QFontEngine::getGlyphPositions(const QGlyphLayout &glyphs, const QTransform &matrix, QTextItem::RenderFlags flags,
                                     QVarLengthArray<glyph_t> &glyphs_out, QVarLengthArray<QFixedPoint> &positions)
 {
diff --git a/src/gui/text/qfontengine_ft.cpp b/src/gui/text/qfontengine_ft.cpp
index de6da88245..03e72546eb 100644
--- a/src/gui/text/qfontengine_ft.cpp
+++ b/src/gui/text/qfontengine_ft.cpp
@@ -61,17 +61,19 @@
 #include FT_TRUETYPE_TABLES_H
 #include FT_TYPE1_TABLES_H
 #include FT_GLYPH_H
+#include FT_MODULE_H
 
 #if defined(FT_LCD_FILTER_H)
 #include FT_LCD_FILTER_H
+#define QT_USE_FREETYPE_LCDFILTER
 #endif
 
 #if defined(FT_CONFIG_OPTIONS_H)
 #include FT_CONFIG_OPTIONS_H
 #endif
 
-#if defined(FT_LCD_FILTER_H)
-#define QT_USE_FREETYPE_LCDFILTER
+#if defined(FT_FONT_FORMATS_H)
+#include FT_FONT_FORMATS_H
 #endif
 
 #ifdef QT_LINUXBASE
@@ -151,6 +153,14 @@ QtFreetypeData *qt_getFreetypeData()
     QtFreetypeData *&freetypeData = theFreetypeData()->localData();
     if (!freetypeData)
         freetypeData = new QtFreetypeData;
+    if (!freetypeData->library) {
+        FT_Init_FreeType(&freetypeData->library);
+#if defined(FT_FONT_FORMATS_H)
+        // Freetype defaults to disabling stem-darkening on CFF, we re-enable it.
+        FT_Bool no_darkening = false;
+        FT_Property_Set(freetypeData->library, "cff", "no-stem-darkening", &no_darkening);
+#endif
+    }
     return freetypeData;
 }
 #endif
@@ -158,8 +168,7 @@ QtFreetypeData *qt_getFreetypeData()
 FT_Library qt_getFreetype()
 {
     QtFreetypeData *freetypeData = qt_getFreetypeData();
-    if (!freetypeData->library)
-        FT_Init_FreeType(&freetypeData->library);
+    Q_ASSERT(freetypeData->library);
     return freetypeData->library;
 }
 
@@ -218,8 +227,6 @@ QFreetypeFace *QFreetypeFace::getFace(const QFontEngine::FaceId &face_id,
         return 0;
 
     QtFreetypeData *freetypeData = qt_getFreetypeData();
-    if (!freetypeData->library)
-        FT_Init_FreeType(&freetypeData->library);
 
     QFreetypeFace *freetype = freetypeData->faces.value(face_id, 0);
     if (freetype) {
@@ -687,6 +694,7 @@ QFontEngineFT::QFontEngineFT(const QFontDef &fd)
     cacheEnabled = env.isEmpty() || env.toInt() == 0;
     m_subPixelPositionCount = 4;
     forceAutoHint = false;
+    stemDarkeningDriver = false;
 }
 
 QFontEngineFT::~QFontEngineFT()
@@ -798,6 +806,17 @@ bool QFontEngineFT::init(FaceId faceId, bool antialias, GlyphFormat format,
             }
         }
     }
+#if defined(FT_FONT_FORMATS_H)
+    const char *fmt = FT_Get_Font_Format(face);
+    if (fmt && qstrncmp(fmt, "CFF", 4) == 0) {
+        FT_Bool no_stem_darkening = true;
+        FT_Error err = FT_Property_Get(qt_getFreetype(), "cff", "no-stem-darkening", &no_stem_darkening);
+        if (err == FT_Err_Ok)
+            stemDarkeningDriver = !no_stem_darkening;
+        else
+            stemDarkeningDriver = false;
+    }
+#endif
 
     fontDef.styleName = QString::fromUtf8(face->style_name);
 
@@ -841,6 +860,11 @@ void QFontEngineFT::setDefaultHintStyle(HintStyle style)
     default_hint_style = style;
 }
 
+bool QFontEngineFT::expectsGammaCorrectedBlending() const
+{
+    return stemDarkeningDriver;
+}
+
 int QFontEngineFT::loadFlags(QGlyphSet *set, GlyphFormat format, int flags,
                              bool &hsubpixel, int &vfactor) const
 {
diff --git a/src/gui/text/qfontengine_ft_p.h b/src/gui/text/qfontengine_ft_p.h
index 32357d0076..47f13eb274 100644
--- a/src/gui/text/qfontengine_ft_p.h
+++ b/src/gui/text/qfontengine_ft_p.h
@@ -252,6 +252,7 @@ private:
                                    QPoint *offset) Q_DECL_OVERRIDE;
     bool hasInternalCaching() const Q_DECL_OVERRIDE { return cacheEnabled; }
     void unlockAlphaMapForGlyph() Q_DECL_OVERRIDE;
+    bool expectsGammaCorrectedBlending() const Q_DECL_OVERRIDE;
 
     void removeGlyphFromCache(glyph_t glyph) Q_DECL_OVERRIDE;
     int glyphMargin(QFontEngine::GlyphFormat /* format */) Q_DECL_OVERRIDE { return 0; }
@@ -311,6 +312,7 @@ protected:
     bool embeddedbitmap;
     bool cacheEnabled;
     bool forceAutoHint;
+    bool stemDarkeningDriver;
 
 private:
     friend class QFontEngineFTRawFont;
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index c0e350f755..514e9424b2 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -254,6 +254,7 @@ public:
     static QByteArray convertToPostscriptFontFamilyName(const QByteArray &fontFamily);
 
     virtual bool hasUnreliableGlyphOutline() const;
+    virtual bool expectsGammaCorrectedBlending() const;
 
     enum HintStyle {
         HintNone,