QGLFrameBufferObject as a QPainterDevice transparent pen problem

Hi there,

I'm using QGLFrameBufferObject as a QPainterDevice like that ;

Code:

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m_pen(QBrush(QColor(255,0,0,80)),10)

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Code:

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//		QGLFramebufferObjectFormat format;
//		format.setAttachment(QGLFramebufferObject::CombinedDepthStencil);
//		format.setSamples(3);
		m_FBO = new QGLFramebufferObject(width(),height()/*, format*/);

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Code:

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QPainter painter(m_FBO);
painter.setRenderHints(QPainter::HighQualityAntialiasing | QPainter::SmoothPixmapTransform | QPainter::TextAntialiasing);
painter.setPen(m_pen);
painter.drawLine(m_start,m_end);

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If i use opaque colors everything is going well. and if i don't use opaque colors in m_pen like that m_pen(QBrush(QColor(255,0,0,80)),10) transparent colors drawing so weird as like attached image;

Attachment 6592

is there any idea what is going wrong ? Thanks ...