[Interest] GLWidget blinking when moving

[baneyue]

Hi guys:

	I'm doing with a customlize title bar combined with a QGLWidget.
	My trouble is that when i drag the title bar, it should behave like
	a native title bar(move its content, i.e. the GLWidget, along with
	itself), BUT in fact, the GLWidget keep blinking and sometimes the
	widget woule *disappear*(move to some area that cannot be seen, out
	of the screen rect), it's weird.

	Here's some basic information:
	* QGLWidget has been wrapped in a dummy widget as th QtDoc says;
	* Both widget has the flags: Frameless & Window;
	* Title bar widget use the geometry of the GLWidget to locate
	itself(in its own paintEvent()), and use GLWidget.move() to change
	the pos of GLWidget in the mouseMoveEvent();
	* widget.update() method is called at every possible place;
	* I tried the customlize title in a common non-openGL widget, the
	widget blinking issue not came to me.

	I know not much about openGL, but it seems to be the problem of
	QGLWidget.

	Any advise would be appreciated.

	Thx.
	baneyue