Optimize getting bearings of a glyph on Windows for true type fonts

Usually, the bearing of a glyph is calculated based on the bounding box
of the glyph. However, retrieving these bounds is a costly operation
on Windows. For true type fonts, we can retrieve the bearings directly
by getting the ABC widths, so as an optimization we implement a new
virtual function in QFontEngine which retrieves the bearings of the
glyph. The default implementation uses boundingBox, but on Windows we
try to take the shortcut.

Reviewed-by: Simon Hausmann

6 files changed, 59 insertions, 11 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index c000457..3ec389f 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -379,6 +379,14 @@ void QFontEngine::getGlyphPositions(const QGlyphLayout &glyphs, const QTransform
     Q_ASSERT(positions.size() == glyphs_out.size());
 }
 
+void QFontEngine::getGlyphBearings(glyph_t glyph, qreal *leftBearing, qreal *rightBearing)
+{
+    glyph_metrics_t gi = boundingBox(glyph);
+    if (leftBearing != 0)
+        *leftBearing = gi.x.toReal();
+    if (rightBearing != 0)
+        *rightBearing = (gi.xoff - gi.x - gi.width).toReal();
+}
 
 glyph_metrics_t QFontEngine::tightBoundingBox(const QGlyphLayout &glyphs)
 {
@@ -1385,6 +1393,12 @@ glyph_metrics_t QFontEngineMulti::boundingBox(const QGlyphLayout &glyphs)
     return overall;
 }
 
+void QFontEngineMulti::getGlyphBearings(glyph_t glyph, qreal *leftBearing, qreal *rightBearing)
+{
+    int which = highByte(glyph);
+    engine(which)->getGlyphBearings(stripped(glyph), leftBearing, rightBearing);
+}
+
 void QFontEngineMulti::addOutlineToPath(qreal x, qreal y, const QGlyphLayout &glyphs,
                                         QPainterPath *path, QTextItem::RenderFlags flags)
 {
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 71ab5a5..e645caf 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -206,6 +206,8 @@ public:
     virtual qreal minLeftBearing() const { return qreal(); }
     virtual qreal minRightBearing() const { return qreal(); }
 
+    virtual void getGlyphBearings(glyph_t glyph, qreal *leftBearing = 0, qreal *rightBearing = 0);
+
     virtual const char *name() const = 0;
 
     virtual bool canRender(const QChar *string, int len) = 0;
@@ -374,6 +376,7 @@ public:
     virtual void recalcAdvances(QGlyphLayout *, QTextEngine::ShaperFlags) const;
     virtual void doKerning(QGlyphLayout *, QTextEngine::ShaperFlags) const;
     virtual void addOutlineToPath(qreal, qreal, const QGlyphLayout &, QPainterPath *, QTextItem::RenderFlags flags);
+    virtual void getGlyphBearings(glyph_t glyph, qreal *leftBearing = 0, qreal *rightBearing = 0);
 
     virtual QFixed ascent() const;
     virtual QFixed descent() const;
diff --git a/src/gui/text/qfontengine_win.cpp b/src/gui/text/qfontengine_win.cpp
index 1a815d3..a133b48 100644
--- a/src/gui/text/qfontengine_win.cpp
+++ b/src/gui/text/qfontengine_win.cpp
@@ -649,6 +649,30 @@ static const ushort char_table[] = {
 
 static const int char_table_entries = sizeof(char_table)/sizeof(ushort);
 
+void QFontEngineWin::getGlyphBearings(glyph_t glyph, qreal *leftBearing, qreal *rightBearing)
+{
+    HDC hdc = shared_dc();
+    SelectObject(hdc, hfont);
+
+#ifndef Q_WS_WINCE
+    if (ttf)
+#endif
+
+    {
+        ABC abcWidths;
+        GetCharABCWidthsI(hdc, glyph, 1, 0, &abcWidths);
+        if (leftBearing)
+            *leftBearing = abcWidths.abcA;
+        if (rightBearing)
+            *rightBearing = abcWidths.abcC;
+    }
+
+#ifndef Q_WS_WINCE
+    else {
+        QFontEngine::getGlyphBearings(glyph, leftBearing, rightBearing);
+    }
+#endif
+}
 
 qreal QFontEngineWin::minLeftBearing() const
 {
diff --git a/src/gui/text/qfontengine_win_p.h b/src/gui/text/qfontengine_win_p.h
index f9d8f8b..f19e48e 100644
--- a/src/gui/text/qfontengine_win_p.h
+++ b/src/gui/text/qfontengine_win_p.h
@@ -106,6 +106,8 @@ public:
     virtual QImage alphaMapForGlyph(glyph_t, const QTransform &xform);
     virtual QImage alphaRGBMapForGlyph(glyph_t t, int margin, const QTransform &xform);
 
+    virtual void getGlyphBearings(glyph_t glyph, qreal *leftBearing = 0, qreal *rightBearing = 0);
+
     int getGlyphIndexes(const QChar *ch, int numChars, QGlyphLayout *glyphs, bool mirrored) const;
     void getCMap();
 
diff --git a/src/gui/text/qfontmetrics.cpp b/src/gui/text/qfontmetrics.cpp
index 41d0af1..44a18de 100644
--- a/src/gui/text/qfontmetrics.cpp
+++ b/src/gui/text/qfontmetrics.cpp
@@ -472,8 +472,9 @@ int QFontMetrics::leftBearing(QChar ch) const
     int nglyphs = 9;
     engine->stringToCMap(&ch, 1, &glyphs, &nglyphs, 0);
     // ### can nglyphs != 1 happen at all? Not currently I think
-    glyph_metrics_t gi = engine->boundingBox(glyphs.glyphs[0]);
-    return qRound(gi.x);
+    qreal lb;
+    engine->getGlyphBearings(glyphs.glyphs[0], &lb);
+    return qRound(lb);
 }
 
 /*!
@@ -506,8 +507,9 @@ int QFontMetrics::rightBearing(QChar ch) const
     int nglyphs = 9;
     engine->stringToCMap(&ch, 1, &glyphs, &nglyphs, 0);
     // ### can nglyphs != 1 happen at all? Not currently I think
-    glyph_metrics_t gi = engine->boundingBox(glyphs.glyphs[0]);
-    return qRound(gi.xoff - gi.x - gi.width);
+    qreal rb;
+    engine->getGlyphBearings(glyphs.glyphs[0], 0, &rb);
+    return qRound(rb);
 }
 
 /*!
@@ -1317,8 +1319,9 @@ qreal QFontMetricsF::leftBearing(QChar ch) const
     int nglyphs = 9;
     engine->stringToCMap(&ch, 1, &glyphs, &nglyphs, 0);
     // ### can nglyphs != 1 happen at all? Not currently I think
-    glyph_metrics_t gi = engine->boundingBox(glyphs.glyphs[0]);
-    return gi.x.toReal();
+    qreal lb;
+    engine->getGlyphBearings(glyphs.glyphs[0], &lb);
+    return lb;
 }
 
 /*!
@@ -1351,8 +1354,10 @@ qreal QFontMetricsF::rightBearing(QChar ch) const
     int nglyphs = 9;
     engine->stringToCMap(&ch, 1, &glyphs, &nglyphs, 0);
     // ### can nglyphs != 1 happen at all? Not currently I think
-    glyph_metrics_t gi = engine->boundingBox(glyphs.glyphs[0]);
-    return (gi.xoff - gi.x - gi.width).toReal();
+    qreal rb;
+    engine->getGlyphBearings(glyphs.glyphs[0], 0, &rb);
+    return rb;
+
 }
 
 /*!
diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index 204effa..3c0e85e 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -1688,9 +1688,9 @@ namespace {
             if (currentPosition <= 0)
                 return;
 
-            glyph_metrics_t gi = fontEngine->boundingBox(currentGlyph());
-            if (gi.isValid())
-                rightBearing = qMin(QFixed(), gi.xoff - gi.x - gi.width);
+            qreal rb;
+            fontEngine->getGlyphBearings(currentGlyph(), 0, &rb);
+            rightBearing = qMin(QFixed(), QFixed::fromReal(rb));
         }
 
         inline void resetRightBearing()