Determine bounding rect of line in Qt

Question

I am drawing a line using QPainterPath between two points as follows:

QPainterPath line;
line.moveTo(start_p);
line.lineTo(end_p);

QPen paintpen(Qt::black);
paintpen.setWidth(1);
painter->setRenderHint(QPainter::Antialiasing);
painter->setBrush(Qt::SolidPattern);
painter->setPen(paintpen);
painter->drawPath(line);

I have defined bounding rect as:

QRectF Line::boundingRect() const
{
 return QRectF(start_p.x(), start_p.y(), end_p.x(), end_p.y());
}

I get line painted correctly when:

start_p.x() < end_p.x() 

and

start_p.y() < end_p.y()

How should the bounding rect be defined so that line is drawn correctly irrespective of the relationship between the coordinates of two points(start_p and end_p)?

Nato

Answer 1

You might try to normalize your rectangle:

QRectF Line::boundingRect() const
{
    return QRectF(start_p.x(), start_p.y(), end_p.x(), end_p.y()).normalized();
}

Gelation

The arguments to this version of QRectF's constructor (doc.qt.io/qt-5/qrectf.html#QRectF-3) are x, y, width, and height. Shouldn't it be QRectF(start_p, end_p) (doc.qt.io/qt-5/qrectf.html#QRectF-2)? – Unsphere

@Mitch, right, it might be QRectF(start_p, end_p) too. – Gelation

Answer 2

You could either:-

• Check for the conditions when the ends are greater than the start points and set the rect appropriately
• Return the QPainterPath's bounding rect
• Use a QGraphicsLineItem instead of reinventing the wheel.

If you just want a line, QGraphicsLineItem is likely the best way to go here.

Shortcoming

The third one is the best! – Adrian

Answer 3

You can use QPainterPath::boundingRect which returns the bounding rectangle of the QPainterPath. You can keep the painter path as a class member and access it in the boundingRect function :

QRectF Line::boundingRect() const
{
     return line.boundingRect();
}

Roi