Using QBrush(const QGradient & gradient) constructor causes a problem

[ajo]

I'm trying to draw an image like the radial gradient one in the Qt gradients example, working with:
Qt 5.0.1 (64 bit) Qt Creator 2.6.2
on a Mac with OS X 10.8.3 (Mountain Lion)

It gives an memory access error and points to the line where the brush is constructed, whether brush is a pointer or not.

ballItem::ballItem()
{
    QGradient gradient;
    gradient.setSpread(QGradient::PadSpread);
 
    // brush = new QBrush(gradient);
    QBrush brush2(gradient);
}

ballItem::ballItem()
{
    QGradient gradient;
    gradient.setSpread(QGradient::PadSpread);

    // brush = new QBrush(gradient);
    QBrush brush2(gradient);
}

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This is the header:

#include <QGraphicsItem>
 
class ballItem : public QGraphicsItem
{
public:
    ballItem();
protected:
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
private:
    QBrush* brush;
};

#include <QGraphicsItem>

class ballItem : public QGraphicsItem
{
public:
    ballItem();
protected:
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
private:
    QBrush* brush;
};

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I was trying to use this QBrush constructor:
QBrush::QBrush(const QGradient & gradient)

I would appreciate it if somebody can show me my error.

---

Added after 40 minutes:

It seems that QConicalGradient, QLinearGradient or QRadialGradient needs to be used, not QGradient, because the QGradient type isn't initialized.
http://lists.trolltech.com/qt-jambi-...ad00025-0.html

[wysota]

So is your problem solved or not?

[ajo]

The "Elastic Nodes Example" provided me with a simpler way to draw a ball with a light spot and a smooth transition to the darker parts.

In that example - Node:: paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *) - QRadialGradient is used:

QRadialGradient gradient(-3, -3, 10);

QRadialGradient gradient(-3, -3, 10);

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My problem is solved, and I think to use QRadialGradient would also work to draw an image like the one in the "Gradients" example. Interestingly though, I see in that example - in void GradientRenderer:aint(QPainter *p) - a QGradient variable is declared and used:

void GradientRenderer:: paint(QPainter *p)
{
    QPolygonF pts = m_hoverPoints->points();
 
    QGradient g;
 
    // and then farther down in the function:
 
    p->setBrush(g);

void GradientRenderer:: paint(QPainter *p)
{
    QPolygonF pts = m_hoverPoints->points();

    QGradient g;

    // and then farther down in the function:

    p->setBrush(g);

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When I tried to do the same, it crashed, because I left out this part:

if (m_gradientType == Qt::LinearGradientPattern) {
        g = QLinearGradient(pts.at(0), pts.at(1));
 
    } else if (m_gradientType == Qt::RadialGradientPattern) {
        g = QRadialGradient(pts.at(0), qMin(width(), height()) / 3.0, pts.at(1));
 
    } else {
        QLineF l(pts.at(0), pts.at(1));
        qreal angle = l.angle(QLineF(0, 0, 1, 0));
        if (l.dy() > 0)
            angle = 360 - angle;
        g = QConicalGradient(pts.at(0), angle);
    }

if (m_gradientType == Qt::LinearGradientPattern) {
        g = QLinearGradient(pts.at(0), pts.at(1));

    } else if (m_gradientType == Qt::RadialGradientPattern) {
        g = QRadialGradient(pts.at(0), qMin(width(), height()) / 3.0, pts.at(1));

    } else {
        QLineF l(pts.at(0), pts.at(1));
        qreal angle = l.angle(QLineF(0, 0, 1, 0));
        if (l.dy() > 0)
            angle = 360 - angle;
        g = QConicalGradient(pts.at(0), angle);
    }

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g is changed to a QLinearGradient or a QRadialGradient or a QConicalGradient.