Consider the following paintEvent() reimplementation:

void TilingWidget::paintEvent(QPaintEvent *event) {
QPainter painter(this);
painter.scale(1.0 / 3.0, 1.0 / 3.0);

for(int i = 0; i < 10; ++i) {
for(int j = 0; j < 10; ++j)

{ QRect area(i * 100, j * 100, 100, 100); QPixmap pix(area.size()); pix.fill(Qt::yellow); painter.fillRect(area, Qt::blue); painter.drawPixmap(area, pix); }

}
}

The expected result is that the entire painted area is yellow, since a yellow pixmap is painted on top of the blue background.

The actual result is that when the painter is scaled down by a number with infinite decimal expansion (1.0 / 3.0, for example), drawPixmap() does not work correctly, and artifacts show up. In the above example, parts of the blue background can be seen in recurring vertical and horizontal lines.