The following code draws text around a QPainterPath
:
QString text = "Short text";
QPainterPath rawPath;
// fill path ...
while (...)
{
double percent = ...;
double angle = rawPath.angleAtPercent(percent);
QPointF point = rawPath.pointAtPercent(percent);
m_painter.save();
m_painter.translate(point);
m_painter.rotate(-angle);
// Version 1:
//m_painter.drawText(0, 0, text.at(currentChar));
// Version 2:
QPainterPath p2;
p2.addText(0, 0, font, text.at(currentChar));
m_painter.drawPath(p2);
m_painter.restore();
}
The graphical result is as expected but the performance of both, Version 1 and Version 2 is very poor. The bottleneck is the QPainter::drawText()
respectively the QPainterPath::addText()
method. Is there a more efficient way to draw text around a path?
Regards,
There is no built-in method to draw a text following a path.
But, if QPainter
is not efficient enough, you can gain some perfs by building a new path with your text and by drawing after your loop (you will not use QPainter::save()
and QPainter::restore()
in a loop):
void paintEvent(QPaintEvent* event)
{
QString text = "Short text";
text = text.repeated(1000); // Check with a very long text
QPainterPath rawPath;
rawPath.addEllipse(QRect(0, 0, 200, 200));
QPainterPath path;
double const step = 1.0 / double(text.length());
double percent = 0.0;
for(QChar const& c: text)
{
double angle = rawPath.angleAtPercent(percent);
QPointF point = rawPath.pointAtPercent(percent);
QTransform mat;
mat.rotate(-angle);
QPainterPath p2;
p2.addText(0, 0, font(), c);
p2 = mat.map(p2);
path.addPath(p2.translated(point));
percent += step;
}
QPainter painter(this);
painter.drawPath(path.translated(100, 100));
}