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Avoid processing-intensive painting of high number of tiny dashes

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When stroking a dashed path, an unnecessary amount of processing would
be spent if there is a huge number of dashes visible, e.g. because of
scaling. Since the dashes are too small to be indivdually visible
anyway, just replace with a semi-transparent solid line for such
cases.

Change-Id: I9e9f7861257ad5bce46a0cf113d1a9d7824911e6
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
(cherry picked from commit f4d791b330d02777fcaf02938732892eb3167e9b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Eirik Aavitsland 2021-04-13 14:23:45 +02:00 committed by Qt Cherry-pick Bot
parent 0ba9a4f832
commit ada12ec960
2 changed files with 69 additions and 9 deletions
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44
src/gui/painting/qpaintengineex.cpp
View File

@ -385,7 +385,7 @@ QPainterState *QPaintEngineEx::createState(QPainterState *orig) const
Q_GUI_EXPORT extern bool qt_scaleForTransform(const QTransform &transform, qreal *scale); // qtransform.cpp
void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)
void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &inPen)
{
#ifdef QT_DEBUG_DRAW
qDebug() << "QPaintEngineEx::stroke()" << pen;
@ -403,6 +403,38 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)
d->stroker.setCubicToHook(qpaintengineex_cubicTo);
}
QRectF clipRect;
QPen pen = inPen;
if (pen.style() > Qt::SolidLine) {
QRectF cpRect = path.controlPointRect();
const QTransform &xf = state()->matrix;
if (pen.isCosmetic()) {
clipRect = d->exDeviceRect;
cpRect.translate(xf.dx(), xf.dy());
} else {
clipRect = xf.inverted().mapRect(QRectF(d->exDeviceRect));
}
// Check to avoid generating unwieldy amount of dashes that will not be visible anyway
QRectF extentRect = cpRect & clipRect;
qreal extent = qMax(extentRect.width(), extentRect.height());
qreal patternLength = 0;
const QList<qreal> pattern = pen.dashPattern();
const int patternSize = qMin(pattern.size(), 32);
for (int i = 0; i < patternSize; i++)
patternLength += qMax(pattern.at(i), qreal(0));
if (pen.widthF())
patternLength *= pen.widthF();
if (qFuzzyIsNull(patternLength)) {
pen.setStyle(Qt::NoPen);
} else if (extent / patternLength > 10000) {
// approximate stream of tiny dashes with semi-transparent solid line
pen.setStyle(Qt::SolidLine);
QColor color(pen.color());
color.setAlpha(color.alpha() / 2);
pen.setColor(color);
}
}
if (!qpen_fast_equals(pen, d->strokerPen)) {
d->strokerPen = pen;
d->stroker.setJoinStyle(pen.joinStyle());
@ -430,14 +462,8 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)
return;
}
if (pen.style() > Qt::SolidLine) {
if (pen.isCosmetic()) {
d->activeStroker->setClipRect(d->exDeviceRect);
} else {
QRectF clipRect = state()->matrix.inverted().mapRect(QRectF(d->exDeviceRect));
d->activeStroker->setClipRect(clipRect);
}
}
if (!clipRect.isNull())
d->activeStroker->setClipRect(clipRect);
if (d->activeStroker == &d->stroker)
d->stroker.setForceOpen(path.hasExplicitOpen());

34
tests/auto/other/lancelot/scripts/tinydashes.qps Normal file
View File

@ -0,0 +1,34 @@
# Version: 1
# CheckVsReference: 5%
path_addEllipse mypath 20.0 20.0 200.0 200.0
save
setPen blue 20 SolidLine FlatCap
pen_setCosmetic true
pen_setDashPattern [ 0.0004 0.0004 ]
setBrush yellow
drawPath mypath
translate 300 0
setRenderHint Antialiasing true
drawPath mypath
restore
path_addEllipse bigpath 200000.0 200000.0 2000000.0 2000000.0
setPen blue 20 DotLine FlatCap
setBrush yellow
save
translate 0 300
scale 0.0001 0.00011
drawPath bigpath
restore
save
translate 300 300
setRenderHint Antialiasing true
scale 0.0001 0.00011
drawPath bigpath
restore