qt画旋转的带箭头的线段

tesb::tesb(QWidget *parent)
	: QWidget(parent)
{
	ui.setupUi(this);
}

void tesb::DrawCustomLine(QPainter& _painter, double _angle, double _len, const QString& _name, const QColor& _color)
{
	// 初始化
	_painter.resetTransform(); // 重设画笔
	_painter.translate(QPoint(300,300));
	_painter.setPen(QPen(Qt::black, 2));

	// 绘制线段
	QLine _line(QPoint(0,0), QPoint(_len,0));
	_painter.rotate(_angle);
	_painter.drawLine(_line);

	// 绘制箭头
	int off_x = 10;
	QPainterPath _path;
	_path.moveTo(_len-off_x, -5);
	_path.lineTo(_len,0);
	_path.lineTo(_len-off_x,5);
	_painter.drawPath(_path);

	// 绘制名称
	_painter.setPen(_color);
	
	QFont _font = _painter.font();
	_font.setPointSize(10);
	_font.setBold(true);
	_painter.setFont(_font);

	_painter.drawText(QPoint(_len-2*off_x,-10), _name);
}

void tesb::paintEvent( QPaintEvent *ev )
{
	QPainter _painter(this);
	_painter.setPen(QPen(Qt::black, 2));
	// 反锯齿
	_painter.setRenderHint(QPainter::Antialiasing);

	// 将画笔中心点移动至(300,300)
	_painter.translate(QPoint(300,300));

	// 绘制中心点
	_painter.drawPoint(QPoint(0,0));
	// 绘制外圆
	_painter.drawEllipse(QRect(-150,-150,300,300));

	DrawCustomLine(_painter, 0, 150, "Da", Qt::red);
	DrawCustomLine(_painter, 123.5, 130, "Db", Qt::green);
	DrawCustomLine(_painter, -45, 30, "Dc", Qt::blue);
	DrawCustomLine(_painter, -145, 60, "Dd", Qt::yellow);

	QWidget::paintEvent(ev);
}