How to draw a rectangle on a graph with XY axes Qt - c++

Question

I want to draw a rectangle on a graph with XY axes using Qt. I have found QCustomPlot widget, but it is not what i need (or i did not understand how to apply it to solve my problem).
Please any suggestions how to make it work?

Answer 1

This is an example of what you need:
#include <QWidget>
#include <QPainter>
class MyPlot : public QWidget
{
Q_OBJECT
public:
MyPlot(QWidget *parent = 0)
: QWidget(parent)
{
}
protected:
void paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.save();
painter.translate(2, height() -2); // 2 pixels between axes and the windows frame
painter.scale(1,-1);
QPen pen;
pen.setWidth(2);
painter.setPen(pen);
// X Axis
painter.drawLine(0,0, width(),0);
// Y Axis
painter.drawLine(0,0, 0,height());
pen.setWidth(4);
painter.setPen(pen);
// Rect
painter.drawRect(10,10, 60,80);
painter.restore();
}
};

Answer 2

You can do it by adding QCPItemRect to QCPLayer of QCustomPlot. It seems to be the easiest solution.

Answer 3

The simplest override paintEvent in QWidget:
void MyWidget::paintEvent(QPaintEvent * event)
{
Q_UNUSED(event);
QPainter painter(this);
painter.drawLine(0, 10, 100, 10);
painter.drawLine(10, 0, 10, 100);
painter.drawRect(20, 20, 30, 30);
}

Answer 4

You can use just the plain QWidget and reimplement it's paintEvent() function. The painting would be realized by the QPainter.
void CMyWidget::paintEvent(QPaintEvent* event)
{
QPainter p(this);
p.drawLine(...);
p.drawRect(...);
p.drawText(...);
}
Or you can use a QGraphicsView / QGraphicsScene framework: http://doc.qt.io/qt-4.8/graphicsview.html