Creating a QSector Class (using Qt and QPaint)

Question

I have created a class name QSector to draw a sector like the following : http://www.philadelphia-reflections.com/images/GDP_Composition_By_Sector_Graph.jpg

QValue is a class with 2 attributes Label (String) and Value (double) the QSector class is composed of 4 attributes and is inherited from QWidget

• QPainter (to draw things)
• QRect (size and position)
• QVector (store all the data of the sector, values and labels)
• Double total (compute the total of QValue's Values (to compute percentage later))

here is the code ::

// <c++>
class QValue
{
public:
    QValue(QString a = "", double b = 0): f_label(a), f_value(b) {}

    double value()  {   return f_value; }
    QString label() {   return f_label; }

    void setValue(double a)  {  f_value = a;    }
    void setLabel(QString a) {  f_label = a;    }

    void set(QString a, double b)   {   f_label = a;    f_value = b;    }

private:
    QString f_label;
    double  f_value;
};

class QSector : public QWidget
{
    Q_OBJECT

public:
    QSector(int width, int height, QWidget *parent = 0)
    : QWidget(parent), f_total(0)
    {
        f_rect = new QRect(1, 1, width - 3 , height - 3);
        this->resize(width, height);
        f_paint = new QPainter;
    }

    void paintEvent(QPaintEvent* event = 0)
    {
        QBrush brush;

        brush.setColor(QColor(25, 25, 255));
        brush.setStyle(Qt::SolidPattern);

        int startAngle  = 0;
        int spanAngle   = 0;

        f_paint->begin(this);

        for (int i = 0; i < f_data.size(); i++)
        {
            int c = ( i * 150) % 255;
            brush.setColor(QColor(c, 25, 255));
            f_paint->setBrush(brush);
    // 5760 = 360 * 16 = 100%;  total = 100% => Value * 5760 / total = span angle
            spanAngle = (5760 * f_data[i].value()) / f_total;

            f_paint->drawPie(*f_rect, startAngle, spanAngle);

            startAngle = spanAngle;
        }

        f_paint->end();
    }

    void add(QString Label, double Value)
    {
        f_data.push_back(QValue(Label, Value));
        f_total = f_total + Value;

        update();   //   => paintEvent();
    }

    void add(QValue a)
    {
        f_data.push_back(a);
        f_total = f_total + a.value();

        update();   //   => paintEvent();
    }

signals:

public slots:

private:
    QPainter *f_paint;
    QRect    *f_rect;

    QVector<QValue>  f_data;
    double  f_total;
};

Everything Compile.

the problem comes when I do ::

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    int w = 300;
    int h = 300;

    QSector test(w, h);

    for (int i = 0, n  = 10; i < n; i++)
        test.add("", 10);

    test.show();

    return app.exec();
}

the program only draws the first 2 parts and stops (the sector should have 10 equal parts it has only 2)

I don't understand why it stops drawing. if I cut the sector in two it works fine but starting with 3 it only draws 2 parts

summary of the problem : https://i.stack.imgur.com/5jyi6.png (image 1, sector divided in 1) (image 2, sector divided in 2) (image 3, sector divided in 3) (image 4, sector divided in 10)

Answer 1

I suspect that

startAngle = spanAngle;

should be

startAngle += spanAngle;

It looks like you're just repainting over the same pie slice over and over at the same angle.