テキスト書けたよありがとう！

graphicsview.cpp

#include <QApplication>
#include <QtWidgets>
#include <QtCore>
#include <QtGui>

class MyView : public QGraphicsView
{
    Q_OBJECT
public:
    MyView() {
        setScene(new QGraphicsScene(-2000, -2000, 4000, 4000));
    }
protected:
    void drawBackground(QPainter *painter, const QRectF &rect) {
        for (int x = static_cast<int>(rect.left() / 10 + 1) * 10; x < rect.right(); x += 10) {
            for (int y = static_cast<int>(rect.top() / 10 + 1) * 10; y < rect.bottom(); y += 10) {
                painter->drawLine(rect.left(), y, rect.right(), y);
                painter->drawLine(x, rect.top(), x, rect.bottom());
                if (y % 50 == 0) {
                    painter->drawText(0, y, QString::number(y));
                    if (x == y) {
                        painter->save();
                        painter->setPen(QPen(Qt::red));
                        painter->setBrush(QBrush(qRgba(128, 0, 0, 50)));
                        painter->drawEllipse(x - 20, y - 20, 40, 40);
                        painter->restore();
                    }
                }
            }
            if (x % 50 == 0)
                painter->drawText(x, 0, QString::number(x));
        }
        QGraphicsView::drawBackground(painter, rect);
    }
};


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MyView v;
    v.resize(200, 200);
    v.show();
    return a.exec();
}

#include "graphicsview.moc"