Why the result of display is not anti-aliased?

[superwave]

grCanvas derived from QGLWidget.

void grCanvas::paintEvent(QPaintEvent* event)
{
	QPainter ipainter(this);
	ipainter.begin(this);
	ipainter.setWindow(QRect(this->translate.X-iMargin,this->translate.Y-iMargin,zoom.X+2*iMargin,zoom.Y+2*iMargin));
 
	//ipainter.setRenderHint(QPainter::SmoothPixmapTransform, true);
	ipainter.setRenderHint(QPainter::Antialiasing);
	CanvasDrawer->RefreshCanvas(this);
 
	CanvasDrawer->RunOpenGL(&ipainter,ShowLens);
	if(ShowLens==TRUE)
	ipainter.drawImage(m_pos - QPointF(m_radius, m_radius), m_lens_image);
}

void grCanvas::paintEvent(QPaintEvent* event)
{
	QPainter ipainter(this);
	ipainter.begin(this);
	ipainter.setWindow(QRect(this->translate.X-iMargin,this->translate.Y-iMargin,zoom.X+2*iMargin,zoom.Y+2*iMargin));
	
	//ipainter.setRenderHint(QPainter::SmoothPixmapTransform, true);
	ipainter.setRenderHint(QPainter::Antialiasing);
	CanvasDrawer->RefreshCanvas(this);

	CanvasDrawer->RunOpenGL(&ipainter,ShowLens);
	if(ShowLens==TRUE)
	ipainter.drawImage(m_pos - QPointF(m_radius, m_radius), m_lens_image);
}

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the code to draw texts, edges, nodes are inside the function RunOpenGL(&ipainter,ShowLens)

the display is like this:

Why the QPainter::Antialiasing fail to act?

Looking for your advice.

Thanks a lot.