Support text decoration in QPainter::drawGlyphs()

In order to support text decorations (overline, underline and strikeout)
in QPainter::drawGlyphs(), we need to call drawTextItemDecoration()
from this function. To support this, it has been generalized to no
longer require a QTextItemInt. We also need to propagate the decoration
attributes of the font from QTextLayout to QGlyphs, since this is not
part of the QFontEngine.

Task-number: QTBUG-12122
Reviewed-by: Kim

1 files changed, 55 insertions, 13 deletions

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index a845842..d6fbab3 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -88,6 +88,10 @@ bool qt_show_painter_debug_output = true;
 
 extern QPixmap qt_pixmapForBrush(int style, bool invert);
 
+static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, QFontEngine *fe,
+                                   QTextCharFormat::UnderlineStyle underlineStyle,
+                                   QTextItemInt::RenderFlags flags, qreal width,
+                                   const QTextCharFormat &charFormat);
 void qt_format_text(const QFont &font,
                     const QRectF &_r, int tf, const QTextOption *option, const QString& str, QRectF *brect,
                     int tabstops, int* tabarray, int tabarraylen,
@@ -5750,6 +5754,8 @@ void qt_draw_glyphs(QPainter *painter, const quint32 *glyphArray, const QPointF
 
 void QPainterPrivate::drawGlyphs(quint32 *glyphArray, QFixedPoint *positions, int glyphCount)
 {
+    Q_Q(QPainter);
+
     updateState(state);
 
     QFontEngine *fontEngine = state->font.d->engineForScript(QUnicodeTables::Common);
@@ -5764,6 +5770,26 @@ void QPainterPrivate::drawGlyphs(quint32 *glyphArray, QFixedPoint *positions, in
         fontEngine = static_cast<QFontEngineMulti *>(fontEngine)->engine(engineIdx);
     }
 
+    QFixed leftMost;
+    QFixed rightMost;
+    QFixed baseLine;
+    for (int i=0; i<glyphCount; ++i) {
+        glyph_metrics_t gm = fontEngine->boundingBox(glyphArray[i]);
+        if (i == 0 || leftMost > positions[i].x)
+            leftMost = positions[i].x;
+
+        // We don't support glyphs that do not share a common baseline. If this turns out to
+        // be a relevant use case, then we need to find clusters of glyphs that share a baseline
+        // and do a drawTextItemDecorations call per cluster.
+        if (i == 0 || baseLine < positions[i].y)
+            baseLine = positions[i].y;
+
+        // We use the advance rather than the actual bounds to match the algorithm in drawText()
+        if (i == 0 || rightMost < positions[i].x + gm.xoff)
+            rightMost = positions[i].x + gm.xoff;
+    }
+
+    QFixed width = rightMost - leftMost;
 
     if (extended != 0) {
         QStaticTextItem staticTextItem;
@@ -5797,6 +5823,21 @@ void QPainterPrivate::drawGlyphs(quint32 *glyphArray, QFixedPoint *positions, in
 
         engine->drawTextItem(QPointF(0, 0), textItem);
     }
+
+    QTextItemInt::RenderFlags flags;
+    if (state->font.underline())
+        flags |= QTextItemInt::Underline;
+    if (state->font.overline())
+        flags |= QTextItemInt::Overline;
+    if (state->font.strikeOut())
+        flags |= QTextItemInt::StrikeOut;
+
+    drawTextItemDecoration(q, QPointF(leftMost.toReal(), baseLine.toReal()),
+                           fontEngine,
+                           (state->font.underline()
+                                ? QTextCharFormat::SingleUnderline
+                                : QTextCharFormat::NoUnderline),
+                           flags, width.toReal(), QTextCharFormat());
 }
 
 /*!
@@ -6322,15 +6363,15 @@ static QPixmap generateWavyPixmap(qreal maxRadius, const QPen &pen)
     return pixmap;
 }
 
-static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const QTextItemInt &ti)
+static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, QFontEngine *fe,
+                                   QTextCharFormat::UnderlineStyle underlineStyle,
+                                   QTextItemInt::RenderFlags flags, qreal width,
+                                   const QTextCharFormat &charFormat)
 {
-    QTextCharFormat::UnderlineStyle underlineStyle = ti.underlineStyle;
     if (underlineStyle == QTextCharFormat::NoUnderline
-        && !(ti.flags & (QTextItem::StrikeOut | QTextItem::Overline)))
+        && !(flags & (QTextItem::StrikeOut | QTextItem::Overline)))
         return;
 
-    QFontEngine *fe = ti.fontEngine;
-
     const QPen oldPen = painter->pen();
     const QBrush oldBrush = painter->brush();
     painter->setBrush(Qt::NoBrush);
@@ -6339,7 +6380,7 @@ static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const
     pen.setWidthF(fe->lineThickness().toReal());
     pen.setCapStyle(Qt::FlatCap);
 
-    QLineF line(pos.x(), pos.y(), pos.x() + ti.width.toReal(), pos.y());
+    QLineF line(pos.x(), pos.y(), pos.x() + width, pos.y());
 
     const qreal underlineOffset = fe->underlinePosition().toReal();
     // deliberately ceil the offset to avoid the underline coming too close to
@@ -6354,21 +6395,21 @@ static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const
         painter->save();
         painter->translate(0, pos.y() + 1);
 
-        QColor uc = ti.charFormat.underlineColor();
+        QColor uc = charFormat.underlineColor();
         if (uc.isValid())
             pen.setColor(uc);
 
         // Adapt wave to underlineOffset or pen width, whatever is larger, to make it work on all platforms
         const QPixmap wave = generateWavyPixmap(qMax(underlineOffset, pen.widthF()), pen);
-        const int descent = (int) ti.descent.toReal();
+        const int descent = (int) fe->descent().toReal();
 
         painter->setBrushOrigin(painter->brushOrigin().x(), 0);
-        painter->fillRect(pos.x(), 0, qCeil(ti.width.toReal()), qMin(wave.height(), descent), wave);
+        painter->fillRect(pos.x(), 0, qCeil(width), qMin(wave.height(), descent), wave);
         painter->restore();
     } else if (underlineStyle != QTextCharFormat::NoUnderline) {
         QLineF underLine(line.x1(), underlinePos, line.x2(), underlinePos);
 
-        QColor uc = ti.charFormat.underlineColor();
+        QColor uc = charFormat.underlineColor();
         if (uc.isValid())
             pen.setColor(uc);
 
@@ -6380,14 +6421,14 @@ static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const
     pen.setStyle(Qt::SolidLine);
     pen.setColor(oldPen.color());
 
-    if (ti.flags & QTextItem::StrikeOut) {
+    if (flags & QTextItem::StrikeOut) {
         QLineF strikeOutLine = line;
         strikeOutLine.translate(0., - fe->ascent().toReal() / 3.);
         painter->setPen(pen);
         painter->drawLine(strikeOutLine);
     }
 
-    if (ti.flags & QTextItem::Overline) {
+    if (flags & QTextItem::Overline) {
         QLineF overLine = line;
         overLine.translate(0., - fe->ascent().toReal());
         painter->setPen(pen);
@@ -6528,7 +6569,8 @@ void QPainter::drawTextItem(const QPointF &p, const QTextItem &_ti)
         else
             d->engine->drawTextItem(p, ti);
     }
-    drawTextItemDecoration(this, p, ti);
+    drawTextItemDecoration(this, p, ti.fontEngine, ti.underlineStyle, ti.flags, ti.width.toReal(),
+                           ti.charFormat);
 
     if (d->state->renderHints != oldRenderHints) {
         d->state->renderHints = oldRenderHints;