Change drawARC starting position

rcourtney

I am making an audio control package and am having trouble figuring out
the coordinate system.

Is there a way to rotate the start of the arc from the 3 o'clock position
to 7 o'clock to reflect modern audio dials?

@void MainWindow::displayARC(int angle)
{
QPixmap pix(61,61);
QPen pen;
pix.fill(Qt::transparent);
QPainter painter(&pix);
painter.setRenderHint(QPainter::Antialiasing);
pen.setWidth(3);
pen.setColor(QColor(220,220,0,255));
painter.setPen(pen);
painter.drawArc(11, 11, 38, 38, 0,
(int) angle * -16);
ui->labelARC->setPixmap(pix);
}@

example:
!http://cdn-data.motu.com/site/images/news/mk3-eq-tab.png(example:)!

image for code snipit:
!https://dl.dropboxusercontent.com/u/83007019/file_407.png(dial)!

dheerendra

Did you get a chance to look at QTransform class ? It may help you.@@

rcourtney

My inability to comprehend the coordinate system is my biggest hurdle.
I will review the transform class. Thanks.

!https://dl.dropboxusercontent.com/u/83007019/TestDials.PNG!

@void MainWindow::displayMark(qreal angle)
{
QPixmap pix(61,61);
QPen pen;
pen.setWidth(3);
pen.setColor(QColor ( 22,22,255,255 ));
pix.fill(Qt::transparent);
QPainter painter(&pix);
painter.translate(pix.width()/2.0,pix.height()/2.0);
painter.rotate(angle +130.0); // Zero is 3:00 position
painter.setPen(pen);
painter.setRenderHint(QPainter::Antialiasing);
painter.drawLine(23.5, 0.0, 3.0, 0.0);
ui->label->setPixmap(pix);
}@

rcourtney

Finally figured it out. Order is important.

@void MainWindow::displayARC(int angle)
{
QPixmap pix(61,61);
pix.fill(Qt::transparent);
QPen pen;
pen.setWidth(3);
pen.setColor(QColor(220,220,0,255));
pix.fill(Qt::transparent);
QPainter painter(&pix);
painter.setRenderHint(QPainter::Antialiasing);
painter.translate(pix.width()/2.0,pix.height()/2.0);
painter.rotate(130.0); // Zero is 3:00 position
painter.setPen(pen);
painter.drawArc(-19, -19, 38, 38, 0,(int)angle * -16);
ui->labelARC->setPixmap(pix);
}

void MainWindow::displayMark(qreal angle)
{
QPixmap pix(61,61);
pix.fill(Qt::transparent);
QPen pen;
pen.setWidth(3);
pen.setColor(QColor(22,22,255,255));
QPainter painter(&pix);
painter.setRenderHint(QPainter::Antialiasing);
painter.translate(pix.width()/2.0,pix.height()/2.0);
painter.rotate(angle +130.0); // Zero is 3:00 position
painter.setPen(pen);
painter.drawLine(23.5, 0.0, 3.0, 0.0);
painter.drawArc(-19, -19, 38, 38, 0,(int)angle * 16);
ui->label->setPixmap(pix);
}
@