Game Programming Using Qt Beginner's Guide

Time for action – transforming the viewport

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 ...