How to change the position of DrawLine according to the size of the widget

[IknowQT]

void wCtrl_Indicator::drawTicks(QPainter* painter)
{
	QBrush		brushActive(QColor(58,62,64));
	QPen		pen(QBrush(brushActive), 2);
	pen.setCapStyle(Qt::FlatCap);
	painter->setPen(pen);

	QPoint c = this->rect().center();
	painter->translate(c);
	painter->rotate(-90);

	for (int s = 0; s <= THICKS_STEP; s++)
	{
		painter->drawLine(15, 0, 25, 0);
		painter->rotate(360 / THICKS_STEP);
	}
}

void wCtrl_Indicator::drawBackGround(QPainter* painter)
{
	QPoint	center = this->rect().center();
	QRect	drawingRect(
		center.x()-20 , 
		center.y()-20 , 
		this->size().height() * 50 / 100,
		this->size().height() * 50 / 100);

	QBrush	brushBackgnd(QColor(82, 95, 99));
	QPen	pen(QBrush(brushBackgnd), PROGRESS_THINKNESS);
	pen.setCapStyle(Qt::FlatCap);

	painter->setPen(pen);
	painter->setBrush(brushBackgnd);
	painter->drawArc(drawingRect, 90 * 16, ConvertAngle(m_nMax) * 16);
}

void wCtrl_Indicator::drawProgress(QPainter* painter)
{
	QPoint	center = this->rect().center();
	QRect	drawingRect(
		center.x() - 20,
		center.y() - 20,
		this->size().height() * 50 / 100,
		this->size().height() * 50 / 100);

	QBrush	brushBackgnd(QColor(75, 147, 191));
	QPen	pen(QBrush(brushBackgnd), PROGRESS_THINKNESS);
	pen.setCapStyle(Qt::FlatCap);

	painter->setPen(pen);
	painter->setBrush(brushBackgnd);
	painter->drawArc(drawingRect, (m_dTransAngle--)* 16, 45 * 16);
}

I made this widget, but if I change the size of the drawarc, the drawline should also be changed to match the size of the drawarc, but that's not possible.
Is there a way to automatically calculate the size?