Qt Rotating text around its center point - c++

Question

I am using Qt 5.6, I want to draw a number of text labels around a circle and rotate the text labels to orientate the text according to its position around the circle, so 12 o'clock would have a 0 degree rotation, 3 o'clock would be rotated 90 degrees, 6 o'clock would be rotated 180 degrees etc.
I am aligning the text around its centre position:
void drawText(QPainter* pobjPainter, qreal fltX, qreal fltY
,int intFlags, const QString* pobjText) {
const qreal fltSize = 32767.0;
QPointF ptfCorner(fltX, fltY - fltSize);
if ( (intFlags & Qt::AlignHCenter) == Qt::AlignHCenter ) {
ptfCorner.rx() -= fltSize / 2.0;
} else if ( (intFlags & Qt::AlignRight) == Qt::AlignRight ) {
ptfCorner.rx() -= fltSize;
}
if ( (intFlags & Qt::AlignVCenter) == Qt::AlignVCenter ) {
ptfCorner.ry() += fltSize / 2.0;
} else if ( (intFlags & Qt::AlignTop) == Qt::AlignTop ) {
ptfCorner.ry() += fltSize;
}
QRectF rctPos(ptfCorner, QSizeF(fltSize, fltSize));
pobjPainter->drawText(rctPos, intFlags, *pobjText);
}
I would like to apply a rotation to the text.
I would like to reproduce something similar to what is shown:
http://www.informit.com/articles/article.aspx?p=1405545&seqNum=2
It seems that the rotate function rotates the entire painter canvas, so the coordinates must take into account the rotation which is really giving me a hard time. I want to position the text around the ellipse and then rotate it, how do I know what the coordinates should be?

Answer 1

Sticking with the clock example you could try something like...
virtual void paintEvent (QPaintEvent *event) override
{
QPainter painter(this);
double radius = std::min(width(), height()) / 3;
for (int i = 0; i < 12; ++i) {
int numeral = i + 1;
double radians = numeral * 2.0 * 3.141592654 / 12;
/*
* Calculate the position of the text centre as it would be required
* in the absence of a transform.
*/
QPoint pos = rect().center() + QPoint(radius * std::sin(radians), -radius * std::cos(radians));
/*
* Set up the transform.
*/
QTransform t;
t.translate(pos.x(), pos.y());
t.rotateRadians(radians);
painter.setTransform(t);
/*
* Specify a huge bounding rectangle centred at the origin. The
* transform should take care of position and orientation.
*/
painter.drawText(QRect(-(INT_MAX / 2), -(INT_MAX / 2), INT_MAX, INT_MAX), Qt::AlignCenter, QString("%1").arg(numeral));
}
}