Let's extend our code so that all future operations focus only on drawing within the border boundaries after the border is drawn. Use the window and
viewport transformation as follows:
void Widget::paintEvent(QPaintEvent *) {
QPainter painter(this);
painter.setRenderHint(QPainter::Antialiasing, true);
QPen pen(Qt::black);
pen.setWidth(4);
painter.setPen(pen);
QRect r = rect().adjusted(10, 10, -10, -10);
painter.drawRoundedRect(r, 20, 10);
painter.save();
r.adjust(2, 2, -2, -2);
painter.setViewport(r);
r.moveTo(0, -r.height()/2);
painter.setWindow(r);
drawChart(&painter, r);
painter.restore();
}Also create a protected method called drawChart():
void Widget::drawChart(QPainter *painter, const QRect &rect) {
painter->setPen(Qt::red);
painter->drawLine(0, 0, rect.width(), 0);
}Let's take a look at our output:
