How to draw triangle points in QtChart?

[NeeMoo]

Hello everyone,

I want to draw some points with triangle symbol, but the marker shape only support circle and rectangle shape.
I can create a triangle shape as QImage and send it to the QBrush of QScatterSeries, but if I want to draw I border, I still can only draw a circular or rectangular border.
Is there anyway I can draw a triangle point with triangle border?

[SGaist]

Hi and welcome to devnet,

If your QImage based triangle does the job, then why not update that QImage with a new triangle with the border painted ? It's essentially a question of setting a pen and a brush to your requested colours.

Hope it helps

[NeeMoo]

@SGaist Hi SGaist, Thank you for your answering.
Maybe I didn't make it clear, I want to draw some triangles with border, and others without border, so I have to use setBorderColor or set Pen of QScatterSeries to add the border in some cases.

[NeeMoo]

@SGaist I rewrited the source code of QtChart and now it works! Thank you all the same!

[SGaist]

What did you modify ?

[Vinod Kuntoji]

@NeeMoo ,

void Widget::paintEvent(QPaintEvent *event){
QPainter painter(this);
QPen pen;
pen.setWidth(4);
pen.setColor(Qt::red);
painter.setBrush(Qt::blue);
painter.setPen(pen);
QPointF *points = new QPointF[3];
points[0] = QPointF(100,50);
points[1] = QPointF(50,150);
points[2] = QPointF(150,150);
painter.drawPolygon(points,3);
}

[NeeMoo]

@SGaist I rewrited the ScatterChartItem and ScatterSeries, added a TriangleMarker:
void ScatterChartItem::createPoints(int count)
{
for (int i = 0; i < count; ++i) {

    QGraphicsItem *item = 0;

    switch (m_shape) {
    case QScatterSeries::MarkerShapeCircle: {
        item = new CircleMarker(0, 0, m_size, m_size, this);
        const QRectF &rect = item->boundingRect();
        item->setPos(-rect.width() / 2, -rect.height() / 2);
        break;
    }
    case QScatterSeries::MarkerShapeRectangle:
        item = new RectangleMarker(0, 0, m_size, m_size, this);
        item->setPos(-m_size / 2, -m_size / 2);
        break;
	case QScatterSeries::MarkerShapeTriangle:
		item = new TriangleMarker(0, 0, m_size, m_size, this);
		item->setPos(-m_size / 2, -m_size / 2);
    default:
        qWarning() << "Unsupported marker type";
        break;
    }
    m_items.addToGroup(item);
}

}

class TriangleMarker : public QGraphicsPolygonItem
{

public:
TriangleMarker(qreal x, qreal y, qreal w, qreal h, ScatterChartItem *parent)
: QGraphicsPolygonItem(QPolygonF() << QPointF(x, y + h) << QPointF(x + w, y + h) << QPointF(x + w / 2.0f, y), parent),
m_parent(parent)
{
setAcceptHoverEvents(true);
setFlag(QGraphicsItem::ItemIsSelectable);
}

protected:
void mousePressEvent(QGraphicsSceneMouseEvent *event)
{
QGraphicsPolygonItem::mousePressEvent(event);
m_parent->markerPressed(this);
m_parent->setMousePressed();
}
void hoverEnterEvent(QGraphicsSceneHoverEvent *event)
{
QGraphicsPolygonItem::hoverEnterEvent(event);
m_parent->markerHovered(this, true);
}
void hoverLeaveEvent(QGraphicsSceneHoverEvent *event)
{
QGraphicsPolygonItem::hoverLeaveEvent(event);
m_parent->markerHovered(this, false);
}
void mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
QGraphicsPolygonItem::mouseReleaseEvent(event);
m_parent->markerReleased(this);
if (m_parent->mousePressed())
m_parent->markerSelected(this);
m_parent->setMousePressed(false);
}
void mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event)
{
QGraphicsPolygonItem::mouseDoubleClickEvent(event);
m_parent->markerDoubleClicked(this);
}

private:
ScatterChartItem *m_parent;
};

But the legend of that maker shape is not correct, so it should have a little work on legend.

[SGaist]

Nice !

Did you consider contributing your changes ?

[NeeMoo]

Yeah of course! But I don't know how to contribute my code, I'm a beginner of programming, haha, could you give me some advice?

[SGaist]

Sure, the starting point is here. Take your time to go through it. The first time setup might take some time but following the documentation it's not that complicated.

[JKappes]

@NeeMoo Nice! I'm also a beginner right now, so could you explain where exactly the data-point is in relation to the triangle? If I'm interpreting your code right, I think it's in the bottom left corner?
Because I would like to have two kinds of TriangleMarker, one pointing up with the data-point at the top corner and one pointing down with the data-point at the bottom corner. To do that I would just have to make two TriangleMarker classes and change the 3 QPoints that make up the QPolygonF, right?