Rely solely on alphaMapBoundingBox in QTextureGlyphCache

We're currently adding a lot of transparent pixels to the cache,
wasting both memory and cpu cycles while drawing. AlphaMapBoundingBox
was introduced to return the exact same bounds as the alphaMapForGlyph
function so we should only rely on this instead of adding arbitrary
padding and margins all over the place.

Windows still has an arbitrary +4 in the its drawGDIGlyph() which
means batching will not work on windows, but at least now
other platforms do not need to suffer.

Change-Id: I714903fa195004400c09c3bf6570e46179775f09
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>

2 files changed, 27 insertions, 6 deletions

diff --git a/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm b/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm
index 8d1c4ed064..9b8f10f588 100644
--- a/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm
+++ b/src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm
@@ -444,18 +444,38 @@ void QCoreTextFontEngine::addGlyphsToPath(glyph_t *glyphs, QFixedPoint *position
     }
 }
 
-QImage QCoreTextFontEngine::imageForGlyph(glyph_t glyph, QFixed subPixelPosition, bool aa, const QTransform &m)
+static void qcoretextfontengine_scaleMetrics(glyph_metrics_t &br, const QTransform &matrix)
 {
-    glyph_metrics_t br = boundingBox(glyph);
-
-    if (m.isScaling()) {
-        qreal hscale = m.m11();
-        qreal vscale = m.m22();
+    if (matrix.isScaling()) {
+        qreal hscale = matrix.m11();
+        qreal vscale = matrix.m22();
         br.width  = QFixed::fromReal(br.width.toReal() * hscale);
         br.height = QFixed::fromReal(br.height.toReal() * vscale);
         br.x      = QFixed::fromReal(br.x.toReal() * hscale);
         br.y      = QFixed::fromReal(br.y.toReal() * vscale);
     }
+}
+
+glyph_metrics_t QCoreTextFontEngine::alphaMapBoundingBox(glyph_t glyph, QFixed pos, const QTransform &matrix, GlyphFormat format)
+{
+    if (matrix.type() > QTransform::TxScale)
+        return QFontEngine::alphaMapBoundingBox(glyph, pos, matrix, format);
+
+    glyph_metrics_t br = boundingBox(glyph);
+    qcoretextfontengine_scaleMetrics(br, matrix);
+
+    br.width = qAbs(qRound(br.width)) + 2;
+    br.height = qAbs(qRound(br.height)) + 2;
+
+    return br;
+}
+
+
+QImage QCoreTextFontEngine::imageForGlyph(glyph_t glyph, QFixed subPixelPosition, bool aa, const QTransform &m)
+{
+
+    glyph_metrics_t br = boundingBox(glyph);
+    qcoretextfontengine_scaleMetrics(br, m);
 
     bool isColorGlyph = glyphFormat == QFontEngineGlyphCache::Raster_ARGB;
     QImage::Format format = isColorGlyph ? QImage::Format_ARGB32_Premultiplied : QImage::Format_RGB32;
diff --git a/src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h b/src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h
index a9b1960491..577bb25e95 100644
--- a/src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h
+++ b/src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h
@@ -96,6 +96,7 @@ public:
     virtual QImage alphaMapForGlyph(glyph_t, QFixed subPixelPosition);
     virtual QImage alphaMapForGlyph(glyph_t glyph, QFixed subPixelPosition, const QTransform &t);
     virtual QImage alphaRGBMapForGlyph(glyph_t, QFixed subPixelPosition, const QTransform &t);
+    glyph_metrics_t alphaMapBoundingBox(glyph_t glyph, QFixed, const QTransform &matrix, GlyphFormat);
     virtual QImage bitmapForGlyph(glyph_t, QFixed subPixelPosition, const QTransform &t);
     virtual qreal minRightBearing() const;
     virtual qreal minLeftBearing() const;