[SOLVED] Painting gradients with QGraphicsItem

[AlexRoot]

Hello everyone,
I want to draw a QGraphicsItem and fill it with a QLinearGradient.
I've subclassed the Item implemented the paint function for testig like this:

    painter->save();

    QLinearGradient gradient(m_BoxSize.topLeft(), m_BoxSize.bottomRight());
    gradient.setColorAt(0, Qt::green);
    gradient.setColorAt(1, Qt::red);

    painter->fillPath(shape(), gradient);
    painter->strokePath(shape(), QPen(Qt::red, 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));

    painter->restore();

m_BoxSize is a member variable of my Item and set to QRectF(0, 0, 40, 40);
and shape() is implemented like this:

    QPainterPath path;
    path.addRoundedRect(m_BoxSize, 5, 5);
    return path;

When I add such an Item to my Scene, I'm getting a red rounded rect without infill.
When I change painter->fillPath(shape(), gradient); to painter->fillPath(shape(), Qt::red); I'm getting a red rounded rect as expected.

Can someone tell me my mistake?

Thank you in advance and kind regards
AlexRoot

Edit: why aren't the code blocks working?

[edit: Fixed coding tags, use ``` SGaist]
->Edit: Thank you :)

[SGaist]

Hi,

Can you share the complete class code ?

[AlexRoot]

Hi,
yes, here it is:

namespace Graphics
{
    namespace Items
    {
        class ClassItem : public QGraphicsItem
        {
        public:
            ClassItem(const QColor &color, const QPoint &position, QGraphicsScene *scene);

            virtual QRectF boundingRect() const override;
            virtual QPainterPath shape() const override;
            virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *item, QWidget *widget) override;

        private:
            QColor m_Color;
            QPoint m_Position;
            QRectF m_BoxSize;
            QPainterPath m_ShapePath;
            QLinearGradient m_TitleGradient;
            QGraphicsScene *m_pScene;

        public slots:
            void resize(const QRectF &newRect);
        };
    }
}

and the implementation

Graphics::Items::ClassItem::ClassItem(const QColor &color, const QPoint &position, QGraphicsScene *scene) :
    m_Color(color),
    m_Position(position),
    m_pScene(scene)
{
    setFlags(ItemIsSelectable | ItemIsMovable);
    setAcceptHoverEvents(true);

    m_TitleGradient.setCoordinateMode(QLinearGradient::ObjectBoundingMode);
    m_TitleGradient.setColorAt(0, Qt::red);
    m_TitleGradient.setColorAt(1, Qt::blue);
    resize(QRectF(0, 0, 40, 40));
}

void Graphics::Items::ClassItem::resize(const QRectF &newRect)
{
    m_BoxSize = newRect;
    m_ShapePath = QPainterPath();
    m_ShapePath.setFillRule(Qt::WindingFill);
    m_ShapePath.addRoundedRect(newRect, 5, 5);

    m_TitleGradient.setStart(newRect.topLeft());
    m_TitleGradient.setFinalStop(newRect.bottomRight());
}

QPainterPath Graphics::Items::ClassItem::shape() const
{
    return m_ShapePath;
}

void Graphics::Items::ClassItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
{
    painter->save();

    painter->fillPath(m_ShapePath, m_TitleGradient);
    painter->strokePath(m_ShapePath, QPen(Qt::red, 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));

    painter->restore();
}

It looks very different now, I've reimplemented it. My problem persists:
the example code "ignores" the fillPath line but
painter->fillPath(m_ShapePath, Qt::green);
works

Kind regards
AlexRoot

[AlexRoot]

Any ideas on that?

Tanks in advance and have a nice day :)

[LuGRU]

Check gradient fill mode:

m_TitleGradient.setCoordinateMode(QLinearGradient::ObjectBoundingMode);
// ...
resize(QRectF(0, 0, 40, 40));

ObjectBoundingMode accepts range 0 -> 1.
Check LogicalMode (default mode).

[AlexRoot]

Thank you for your answere. I've already tried that but it wasn't the solution. I've figured out that the problem occures when turning on OpenGL rendering. I guess it has to do with my hibryd graphic system. My main card has some serious problems so I can't run Optirun right now and I guess my secondary GPU does not support the required features (only OpenGL 3.X).
I'm not shure about that but as I said: turning off the OpenGL rendering solved that problem for me. Maybe it helps others.

Have a nice day everyone