get openGL screen size

def getScreenRes(panel):
	m3v = OpenMayaUI.M3dView.active3dView()
	OpenMayaUI.M3dView.getM3dViewFromModelPanel(panel, m3v)
 
	xPtr = OpenMaya.MScriptUtil().asUintPtr()
	yPtr = OpenMaya.MScriptUtil().asUintPtr()
	widthPtr = OpenMaya.MScriptUtil().asUintPtr()
	heightPtr = OpenMaya.MScriptUtil().asUintPtr()
 
	m3v.viewport(xPtr, yPtr, widthPtr, heightPtr)
 
	viewWidth = OpenMaya.MScriptUtil().getUint( widthPtr )
	viewHeight = OpenMaya.MScriptUtil().getUint( heightPtr )
 
	return (float(viewWidth), float(viewHeight))