QT Rotating Pie of a rectangle without shifting center

Question

I would like to make an application which includes rotation widget inside a circle. I started this with the AnalogClock example in qt. I wouldd like to rotate a quarter pie (quarter circle) instead of gauge. My problem is I cannot locate the pie in the center of my circle. Below picture, I barely locate the pi in the center of circle but I would like to make the pi bigger than below picture.

enter image description here I realized that all paintings locate inside of rectangle like below. enter image description here When I change the drawPie function parameters rectangle's location change and rotates based on on edge point. I can make the ractange bigger but this time drawPie center changes too like the last visual. enter image description here

You can check the code below. It is modifed from the AnalogClock example. I would like to draw a quarter pie and make it the rotate endlessly. Any help will be appreciated. If you have a better opinion, I would like hear that too.

AnalogClock::AnalogClock(QWidget *parent) :
QWidget(parent),
ui(new Ui::AnalogClock)
{
ui->setupUi(this);

QTimer *timer = new QTimer(this);

connect(timer, &QTimer::timeout, this, QOverload<>::of(&AnalogClock::update));

timer->start(1000);

setWindowTitle(tr("Analog Clock"));
resize(200, 200);
 }

void AnalogClock::paintEvent(QPaintEvent *)
{



   QColor minuteColor(0, 127, 127, 191);

   int side = qMin(width(), height());
   QTime time = QTime::currentTime();

QPainter painter(this);

painter.setRenderHint(QPainter::Antialiasing);

painter.translate(width() / 2, height() / 2);

painter.scale(side / 200.0, side / 200.0);


painter.setPen(Qt::NoPen);

qreal radius=10;
qreal startAngle=0;
qreal span=60;




for (int i = 0; i < 12; ++i) {
    painter.drawLine(88, 0, 96, 0);
    painter.rotate(30.0);
}


painter.setBrush(minuteColor);


painter.save();

painter.rotate(6.0 *  time.second() );
//painter.drawConvexPolygon(minuteHand, 3);

QRect rect( -radius, -radius, radius*10, radius*10);

painter.drawPie( rect, startAngle*16, span*16 );


   // painter.fillRect(rect,QBrush(Qt::green));
painter.restore();



painter.setPen(minuteColor);



for (int j = 0; j < 60; ++j) {
        painter.drawLine(92, 0, 96, 0);
    painter.rotate(6.0);
  }  

  }

user_18181128 · Answer

The drawPie() function takes a rectangle that defines the hypothetical full circle in which the pie (slice) will be painted. In this example, we want that circle to be the same as the full clock circle - same size, same center. Now the code has normalized the coordinate system for us, so that the clock center point is at (0, 0), and the radius is 100. So we need a rectangle that has its center point in (0,0) and sides that are 2*radius long. That is:

QRect rect(-100, -100, 200, 200);

Changing the rect in the code sample to that fixes the basic issue.

QRect rect(-100, -100, 200, 200);

Changing the rect in the code sample to that fixes the basic issue.

QT Rotating Pie of a rectangle without shifting center

1 Answers