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void CQt3dText::draw(QGLPainter *painter, const QString& _str, const QVector3D& coords, const QFont& _font, const QPen& _pen, const Qt::Alignment& align)
{
	if (_str.isEmpty()) 
		return;

	QFontMetrics fm(_font);
	QRect rect = fm.boundingRect(_str); // text bounding box
	rect.adjust(0, 0, 1, 1);

	QImage image(rect.size(), QImage::Format_ARGB32);
	image.fill(0); // set to transparent

	// Draw the text on an image
	QPainter p2d(&image);
	p2d.setFont(_font);
	p2d.setPen(_pen);
	p2d.drawText(0, 0, rect.width(), rect.height(), Qt::AlignCenter, _str);
	p2d.end();

	// Get viewport
	GLint view[4];
	glGetIntegerv(GL_VIEWPORT, view);

	// Convert the object coordinate to screen coordinate
	GLdouble winx, winy, winz; // the screen coordinate of the object
	QMatrix4x4 model = painter->modelViewMatrix().top();
	QMatrix4x4 proj = painter->projectionMatrix().top();

	GLdouble modelMatrix[16];
	for (int i = 0; i < 16; i++)
		modelMatrix[i] = model.data()[i];

	GLdouble projMatrix[16];
	for (int i = 0; i < 16; i++)
		projMatrix[i] = proj.data()[i];

	gluProject(coords.x(), coords.y(), coords.z(),
		modelMatrix, projMatrix, view,
		&winx, &winy, &winz);

	// Define the font rectangle
	int x = (int) winx, y = (int) winy;

	if (align & Qt::AlignLeft){
		x -= rect.width();
	}
	if (align & Qt::AlignTop){
		y -= rect.height();
	}
	if (align & Qt::AlignHCenter){
		x -= rect.width() / 2;
	}
	if (align & Qt::AlignVCenter){
		y -= rect.height() / 2;
	}

	QVector2DArray vertices;
	vertices.append(x, y);
	vertices.append(x, y + rect.height());
	vertices.append(x + rect.width(), y + rect.height());
	vertices.append(x + rect.width(), y);

	// Texture coordinates
	QVector2DArray texCoord;
	texCoord.append(0.0f, 0.0f);
	texCoord.append(0.0f, 1.0f);
	texCoord.append(1.0f, 1.0f);
	texCoord.append(1.0f, 0.0f);

	// Map the image to texture
	QGLTexture2D texture;
	texture.setImage(image);

	// Set projection matrix stack
	painter->modelViewMatrix().push();
	painter->modelViewMatrix().setToIdentity();

	// Use ortho projection to draw the text
	QMatrix4x4 projm;
	projm.ortho(view[0], view[2], view[1], view[3], 0, 1);

	painter->projectionMatrix().push();
	painter->projectionMatrix() = projm;

	// Enable blend to make the background transparency of the text
	glEnable(GL_BLEND);
	glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
	painter->clearAttributes();
	painter->setStandardEffect(QGL::FlatReplaceTexture2D);
	texture.bind();
	painter->setVertexAttribute(QGL::Position, vertices);
	painter->setVertexAttribute(QGL::TextureCoord0, texCoord);
	painter->draw(QGL::TriangleFan, 4);
	painter->setStandardEffect (QGL::FlatColor);
	glBindTexture(GL_TEXTURE_2D, 0);
	glDisable(GL_BLEND);

	// Restore the matrix stack
	painter->projectionMatrix().pop();
	painter->modelViewMatrix().pop();
}