Refactor lockedAlphaMapForGlyph

Simply return a Glyph pointer and not a QImage to avoid allocating and
deleting lots of d pointers for QImage when drawing text. Saves one
new/delete pair per glyph drawn and speeds up text drawing by 10% for
relatively large glyphs (probably more for smaller ones).

The qtext::paintLayoutToPixmap() benchmark shows a 16% improvement
in performance with this change.

Renamed the method to glyphData().

Change-Id: I7a353de521e4f4321c770fb1ac6043d33f6f332c
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

2 files changed, 8 insertions, 53 deletions

diff --git a/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp b/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
index ef80d68bfe..e132442e37 100644
--- a/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
+++ b/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
@@ -106,7 +106,7 @@ static bool ft_getSfntTable(void *user_data, uint tag, uchar *buffer, uint *leng
     return result;
 }
 
-static QFontEngineFT::Glyph emptyGlyph = {0, 0, 0, 0, 0, 0, 0, 0};
+static QFontEngineFT::Glyph emptyGlyph;
 
 static const QFontEngine::HintStyle ftInitialDefaultHintStyle =
 #ifdef Q_OS_WIN
@@ -556,11 +556,6 @@ void QFreetypeFace::addBitmapToPath(FT_GlyphSlot slot, const QFixedPoint &point,
                        slot->bitmap.buffer, slot->bitmap.pitch, slot->bitmap.width, slot->bitmap.rows, path);
 }
 
-QFontEngineFT::Glyph::~Glyph()
-{
-    delete [] data;
-}
-
 struct LcdFilterDummy
 {
     static inline void filterPixel(uchar &, uchar &, uchar &)
@@ -1986,11 +1981,10 @@ static inline QImage alphaMapFromGlyphData(QFontEngineFT::Glyph *glyph, QFontEng
     return img;
 }
 
-QImage *QFontEngineFT::lockedAlphaMapForGlyph(glyph_t glyphIndex, QFixed subPixelPosition,
-                                              QFontEngine::GlyphFormat neededFormat,
-                                              const QTransform &t, QPoint *offset)
+QFontEngine::Glyph *QFontEngineFT::glyphData(glyph_t glyphIndex, QFixed subPixelPosition,
+                                             QFontEngine::GlyphFormat neededFormat, const QTransform &t)
 {
-    Q_ASSERT(currentlyLockedAlphaMap.isNull());
+    Q_ASSERT(cacheEnabled);
 
     if (isBitmapFont())
         neededFormat = Format_Mono;
@@ -2000,33 +1994,10 @@ QImage *QFontEngineFT::lockedAlphaMapForGlyph(glyph_t glyphIndex, QFixed subPixe
         neededFormat = Format_A8;
 
     Glyph *glyph = loadGlyphFor(glyphIndex, subPixelPosition, neededFormat, t);
-
-    if (offset != 0 && glyph != 0)
-        *offset = QPoint(glyph->x, -glyph->y);
-
-    currentlyLockedAlphaMap = alphaMapFromGlyphData(glyph, neededFormat);
-
-    const bool glyphHasGeometry = glyph != nullptr && glyph->height != 0 && glyph->width != 0;
-    if (!cacheEnabled && glyph != &emptyGlyph) {
-        currentlyLockedAlphaMap = currentlyLockedAlphaMap.copy();
-        delete glyph;
-    }
-
-    if (!glyphHasGeometry)
+    if (!glyph || !glyph->width || !glyph->height)
         return nullptr;
 
-    if (currentlyLockedAlphaMap.isNull())
-        return QFontEngine::lockedAlphaMapForGlyph(glyphIndex, subPixelPosition, neededFormat, t, offset);
-
-    QImageData *data = currentlyLockedAlphaMap.data_ptr();
-    data->is_locked = true;
-
-    return &currentlyLockedAlphaMap;
-}
-
-void QFontEngineFT::unlockAlphaMapForGlyph()
-{
-    QFontEngine::unlockAlphaMapForGlyph();
+    return glyph;
 }
 
 static inline bool is2dRotation(const QTransform &t)
diff --git a/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h b/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h
index 109bae86e9..2863d206d2 100644
--- a/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h
+++ b/src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h
@@ -129,20 +129,6 @@ private:
 class QFontEngineFT : public QFontEngine
 {
 public:
-
-    /* we don't cache glyphs that are too large anyway, so we can make this struct rather small */
-    struct Glyph {
-        ~Glyph();
-        int linearAdvance : 22;
-        unsigned char width;
-        unsigned char height;
-        short x;
-        short y;
-        short advance;
-        signed char format;
-        uchar *data;
-    };
-
     struct GlyphInfo {
         int             linearAdvance;
         unsigned short  width;
@@ -241,11 +227,9 @@ private:
                                         QFixed subPixelPosition,
                                         const QTransform &matrix,
                                         QFontEngine::GlyphFormat format) override;
-    QImage *lockedAlphaMapForGlyph(glyph_t glyph, QFixed subPixelPosition,
-                                   GlyphFormat neededFormat, const QTransform &t,
-                                   QPoint *offset) override;
+    Glyph *glyphData(glyph_t glyph, QFixed subPixelPosition,
+                     GlyphFormat neededFormat, const QTransform &t) override;
     bool hasInternalCaching() const override { return cacheEnabled; }
-    void unlockAlphaMapForGlyph() override;
     bool expectsGammaCorrectedBlending() const override;
 
     void removeGlyphFromCache(glyph_t glyph) override;