setWindow 为什么会影响 brush 效果？ [复制链接]

实验代码：

void paint_test::paintEvent(QPaintEvent * e)
{
  QPainter painter(this);
  painter.setPen(Qt::red);

  QBrush brush(Qt::Dense6Pattern);
  brush.setColor(Qt::blue);
  painter.setBrush(brush);

  painter.setWindow(0, 0, 1000, 1000);
  painter.drawRect(50, 50, 100, 200);

  painter.setWindow(0, 0, 2000, 2000);
  painter.drawRect(500, 100, 200, 400);

  painter.setWindow(0, 0, 3000, 3000);
  painter.drawRect(1350, 150, 300, 600);

  painter.setWindow(0, 0, 4000, 4000);
  painter.drawRect(2600, 200, 400, 800);

  painter.setWindow(0, 0, 5000, 5000);
  painter.drawRect(4250, 250, 500, 1000);
}

画图结果显示 window 大小对 brush 的效果有较大影响。

能否帮忙解释一下原因和解决办法？