Qt简单绘图，圆形笔头的设置

void Painter::paintEvent(QPaintEvent *e)
{
qDebug()<<"************";
QPainter painter(this);

//绘线
painter.drawLine(0,0,400,400);
//绘矩形
painter.drawRect(0,0,400,400);
//绘圆
painter.drawEllipse(0,0,400,400);
//绘椭圆
//painter.drawEllipse(0,0,400,300);
painter.drawEllipse(QPoint(200,200), 200, 150);

//设置绘笔大小，颜色
QPen pen = painter.pen();
pen.setColor(Qt::gray);
pen.setWidth(20);
pen.setCapStyle(Qt::RoundCap);//设置绘笔线头为圆角
painter.setPen(pen);

//0开始位置为右边水平方向， 跨度为正逆时针， 为负顺时针
painter.drawArc(400,10,200,200,0,360*16);  //圆角一度==弧度16

pen.setColor(Qt::green);
painter.setPen(pen);
painter.drawArc(400,10,200,200,180*16,-len*16);

}