Re-enabled antialiasing for large font sizes in OpenGL paint engine.

In 4.4 alphaMapForGlyph() would return valid images for any font size,
but this was changed in 4.5, forcing us to use the path fallback
instead. This lead to non-antialiased fonts when not using a
multisample-enabled GL format. This patch re-introduces the
alphaMapForGlyph() fallback in QFontEngine from 4.4 which uses the
raster paint engine to draw the glyph.

Task-number: 247083
Reviewed-by: Trond

4 files changed, 47 insertions, 7 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 47fe5c2..d7a9c23 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -624,6 +624,45 @@ QImage QFontEngine::alphaRGBMapForGlyph(glyph_t glyph, int /* margin */, const Q
     return rgbMask;
 }
 
+QImage QFontEngine::alphaMapForGlyph(glyph_t glyph)
+{
+    glyph_metrics_t gm = boundingBox(glyph);
+    int glyph_x = qFloor(gm.x.toReal());
+    int glyph_y = qFloor(gm.y.toReal());
+    int glyph_width = qCeil((gm.x + gm.width).toReal()) -  glyph_x;
+    int glyph_height = qCeil((gm.y + gm.height).toReal()) - glyph_y;
+
+    if (glyph_width <= 0 || glyph_height <= 0)
+        return QImage();
+    QFixedPoint pt;
+    pt.x = 0;
+    pt.y = -glyph_y; // the baseline
+    QPainterPath path;
+    QImage im(glyph_width + qAbs(glyph_x) + 4, glyph_height, QImage::Format_ARGB32_Premultiplied);
+    im.fill(Qt::transparent);
+    QPainter p(&im);
+    p.setRenderHint(QPainter::Antialiasing);
+    addGlyphsToPath(&glyph, &pt, 1, &path, 0);
+    p.setPen(Qt::NoPen);
+    p.setBrush(Qt::black);
+    p.drawPath(path);
+    p.end();
+
+    QImage indexed(im.width(), im.height(), QImage::Format_Indexed8);
+    QVector<QRgb> colors(256);
+    for (int i=0; i<256; ++i)
+        colors[i] = qRgba(0, 0, 0, i);
+    indexed.setColorTable(colors);
+
+    for (int y=0; y<im.height(); ++y) {
+        uchar *dst = (uchar *) indexed.scanLine(y);
+        uint *src = (uint *) im.scanLine(y);
+        for (int x=0; x<im.width(); ++x)
+            dst[x] = qAlpha(src[x]);
+    }
+
+    return indexed;
+}
 
 void QFontEngine::removeGlyphFromCache(glyph_t)
 {
diff --git a/src/gui/text/qfontengine_ft.cpp b/src/gui/text/qfontengine_ft.cpp
index cb0b436..de03a3c 100644
--- a/src/gui/text/qfontengine_ft.cpp
+++ b/src/gui/text/qfontengine_ft.cpp
@@ -1788,9 +1788,11 @@ QImage QFontEngineFT::alphaMapForGlyph(glyph_t g)
 
     GlyphFormat glyph_format = antialias ? Format_A8 : Format_Mono;
 
-    Glyph *glyph = loadGlyph(g, glyph_format);
-    if (!glyph)
-        return QImage();
+    Glyph *glyph = defaultGlyphSet.outline_drawing ? 0 : loadGlyph(g, glyph_format);
+    if (!glyph) {
+        unlockFace();
+        return QFontEngine::alphaMapForGlyph(g);
+    }
 
     const int pitch = antialias ? (glyph->width + 3) & ~3 : ((glyph->width + 31)/32) * 4;
 
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 176c728..dc18991 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -178,7 +178,7 @@ public:
      * Create a qimage with the alpha values for the glyph.
      * Returns an image indexed_8 with index values ranging from 0=fully transparant to 255=opaque
      */
-    virtual QImage alphaMapForGlyph(glyph_t) = 0;
+    virtual QImage alphaMapForGlyph(glyph_t);
     virtual QImage alphaMapForGlyph(glyph_t, const QTransform &t);
     virtual QImage alphaRGBMapForGlyph(glyph_t, int margin, const QTransform &t);
 
diff --git a/src/opengl/qpaintengine_opengl.cpp b/src/opengl/qpaintengine_opengl.cpp
index ec6e33b..5a212f5 100644
--- a/src/opengl/qpaintengine_opengl.cpp
+++ b/src/opengl/qpaintengine_opengl.cpp
@@ -5068,9 +5068,8 @@ void QOpenGLPaintEngine::drawTextItem(const QPointF &p, const QTextItem &textIte
 
     // fall back to drawing a polygon if the scale factor is large, or
     // we use a gradient pen
-    if (ti.fontEngine->fontDef.pixelSize >= 64
-        || (d->matrix.det() > 1) || (d->pen_brush_style >= Qt::LinearGradientPattern
-                                     && d->pen_brush_style <= Qt::ConicalGradientPattern)) {
+    if ((d->matrix.det() > 1) || (d->pen_brush_style >= Qt::LinearGradientPattern
+                                  && d->pen_brush_style <= Qt::ConicalGradientPattern)) {
         QPaintEngine::drawTextItem(p, textItem);
         return;
     }