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, 20 insertions, 28 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 5506d88f02..1895ac8283 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -923,29 +923,10 @@ QFixed QFontEngine::subPixelPositionForX(QFixed x) const
     return subPixelPosition;
 }
 
-QImage *QFontEngine::lockedAlphaMapForGlyph(glyph_t glyph, QFixed subPixelPosition,
-                                            QFontEngine::GlyphFormat neededFormat,
-                                            const QTransform &t, QPoint *offset)
+QFontEngine::Glyph *QFontEngine::glyphData(glyph_t, QFixed,
+                                           QFontEngine::GlyphFormat, const QTransform &)
 {
-    Q_ASSERT(currentlyLockedAlphaMap.isNull());
-    if (neededFormat == Format_None)
-        neededFormat = Format_A32;
-
-    if (neededFormat != Format_A32)
-        currentlyLockedAlphaMap = alphaMapForGlyph(glyph, subPixelPosition, t);
-    else
-        currentlyLockedAlphaMap = alphaRGBMapForGlyph(glyph, subPixelPosition, t);
-
-    if (offset != 0)
-        *offset = QPoint(0, 0);
-
-    return &currentlyLockedAlphaMap;
-}
-
-void QFontEngine::unlockAlphaMapForGlyph()
-{
-    Q_ASSERT(!currentlyLockedAlphaMap.isNull());
-    currentlyLockedAlphaMap = QImage();
+    return nullptr;
 }
 
 QImage QFontEngine::alphaMapForGlyph(glyph_t glyph)
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 682395ece6..48dcdbeff7 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -124,6 +124,22 @@ public:
     };
     Q_DECLARE_FLAGS(ShaperFlags, ShaperFlag)
 
+    /* Used with the Freetype font engine. We don't cache glyphs that are too large anyway, so we can make this struct rather small */
+    struct Glyph {
+        Glyph() = default;
+        ~Glyph() { delete [] data; }
+        short linearAdvance = 0;
+        unsigned char width = 0;
+        unsigned char height = 0;
+        short x = 0;
+        short y = 0;
+        short advance = 0;
+        signed char format = 0;
+        uchar *data = nullptr;
+    private:
+        Q_DISABLE_COPY(Glyph);
+    };
+
     virtual ~QFontEngine();
 
     inline Type type() const { return m_type; }
@@ -191,11 +207,7 @@ public:
     virtual QImage alphaMapForGlyph(glyph_t, QFixed subPixelPosition, const QTransform &t);
     virtual QImage alphaRGBMapForGlyph(glyph_t, QFixed subPixelPosition, const QTransform &t);
     virtual QImage bitmapForGlyph(glyph_t, QFixed subPixelPosition, const QTransform &t, const QColor &color = QColor());
-    virtual QImage *lockedAlphaMapForGlyph(glyph_t glyph, QFixed subPixelPosition,
-                                           GlyphFormat neededFormat,
-                                           const QTransform &t = QTransform(),
-                                           QPoint *offset = 0);
-    virtual void unlockAlphaMapForGlyph();
+    virtual Glyph *glyphData(glyph_t glyph, QFixed subPixelPosition, GlyphFormat neededFormat, const QTransform &t);
     virtual bool hasInternalCaching() const { return false; }
 
     virtual glyph_metrics_t alphaMapBoundingBox(glyph_t glyph, QFixed /*subPixelPosition*/, const QTransform &matrix, GlyphFormat /*format*/)
@@ -346,7 +358,6 @@ public:
     void loadKerningPairs(QFixed scalingFactor);
 
     GlyphFormat glyphFormat;
-    QImage currentlyLockedAlphaMap;
     int m_subPixelPositionCount; // Number of positions within a single pixel for this cache
 
     inline QVariant userData() const { return m_userData; }