Center of the screen, from the point of view of the camera, at z = 0

Property definitions

gamnit $ UICamera :: center=
	# Center of the screen, from the point of view of the camera, at z = 0
	var center: IPoint3d[Float] = new CameraAnchor(self, 0.5, -0.5)
lib/gamnit/cameras.nit:238,2--239,64