Qt DrawPie location and rotation issue

[star673]

Hello all,

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.

I realized that all paintings locate inside of rectangle like below.

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.

![Screenshot from 2022-03-3

0 10-26-59.png](https://ddgobkiprc33d.cloudfront.net/8e3b33a3-3cc7-4d3f-9ca5-475f3df170bc.png)

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);
    }

}

[hskoglund]

Hi, I think it's easier if you use the QGraphicsView/QGraphicsScene stuff, made a sample program for you:
Start with an empty vanilla widgets app, then change your mainwindow.cpp to look like this:

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include "qgraphicsview.h"
#include "qgraphicsscene.h"
#include "QGraphicsLineItem"
#include "qvector.h"
#include "qtimer.h"

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

    auto graphicsView = new QGraphicsView(this);
    graphicsView->setGeometry(0,0,width(),height());
    auto scene = new QGraphicsScene(this);

    auto diameter          = qMin(graphicsView->width(),graphicsView->height()) / 1.05;
    auto radius            = diameter / 2;
    auto minuteLineLength  = radius / 20;
    auto minuteLineWidth   = 1;
    auto pieLineLength     = radius - minuteLineLength;
    auto pieLineWidth      = 5;
    auto origo             = QPointF(radius, radius);
    auto timerMilliseconds = 33;   // <--- the speed (33 means one rotation takes 2 seconds) 

// draw the minutes
    for (int m = 0; (m < 60); ++m)
    {
        auto degrees = m * 6 - 90;   // start at 12 o'clock (north)
        auto radians = (degrees / 360.0f) * 2 * 3.141592653;
        auto point0 = origo + QPointF(pieLineLength * cos(radians),pieLineLength * sin(radians));
        auto point1 = origo + QPointF(radius    * cos(radians),radius    * sin(radians));
        scene->addLine(QLineF(point0,point1),QPen(QBrush(Qt::black),minuteLineWidth));
    }

// store the pie lines here
    QList<QGraphicsLineItem*> lPieLines;

// draw the pie lines
    for (int p = 0; (p < 360); ++p)
    {
        auto degrees = p - 90;   // start at 12 o'clock (north)
        auto radians = (degrees / 360.0f) * 2 * 3.141592653;
        auto point0 = origo;
        auto point1 = origo + QPointF(pieLineLength * cos(radians),pieLineLength * sin(radians));
        lPieLines.append(scene->addLine(QLineF(point0,point1),QPen(QBrush(Qt::green),pieLineWidth)));

        lPieLines.constLast()->setVisible(p < 90);
    }

// all lines added, set the scene
    graphicsView->setScene(scene);

// start the party
    auto timer = new QTimer(this);
    connect(timer,&QTimer::timeout,this,[lPieLines]
    {
        static int degrees = 0;

    // step clockwise
        ++degrees;

    // go thru all of the pie lines
        for (int l = 0; (l < 360); ++l)
            lPieLines.at((l + degrees) % 360)->setVisible(l < 90);
    } );
    timer->start(timerMilliseconds);
}

MainWindow::~MainWindow()
{
    delete ui;
}

and it should look like this: (and rotate nicely :-)

[ELIF]

@hskoglund said in Qt DrawPie location and rotation issue:

for (int m = 0; (m < 60); ++m)
{
auto degrees = m * 6 - 90; // start at 12 o'clock (north)
auto radians = (degrees / 360.0f) * 2 * 3.141592653;
auto point0 = origo + QPointF(pieLineLength * cos(radians),pieLineLength * sin(radians));
auto point1 = origo + QPointF(radius * cos(radians),radius * sin(radians));
scene->addLine(QLineF(point0,point1),QPen(QBrush(Qt::black),minuteLineWidth));
}

Thank you very much :) Really appreciate it ! Best regards.

[hskoglund]

Glad you liked it, it's a fun little demo.

BTW, I realized the timer code it a bit wasteful, it hides/shows all the 360 pie lines every time, but actually you only need to update the edges (the forward edge: one line needs to be turned on and the line at trailing edge needs to be hidden).

So here is a better optimized "start the party" code:

/ start the party (revised version)
    auto timer = new QTimer(this);
    connect(timer,&QTimer::timeout,this,[lPieLines]
    {
        static int degrees = 0;

        lPieLines.at((0 +  degrees) % 360)->setVisible(false);
        lPieLines.at((90 + degrees) % 360)->setVisible(true);

    // rotate once clockwise
        ++degrees;
    } );

    timer->start(timerMilliseconds);

Also I was wrong stating that a full rotation with a milleseconds setting of 33 takes 2 seconds, of course it should be 12 seconds (i.e. 30 per second for a total of 360 steps).

[star673]

@hskoglund

Thank you so much sir. You helped me a lot. Best wishes.

[ELIF]

This post is deleted!