I agree with Vishnu.. AFAIK, there is no 3D line primitive in M3G API. So, you'd have to make at least a couple 3D quads to make a line, so at least one of them is visible at all times. If these lines are static, you can just incorporate the quads into your model. If the lines are dynamic (change in real time), then you've got problems, because you'll have to create a new mesh every frame. This would probably end up pretty slow, since M3G probably does some sort of processing when a new mesh is created.. Never tried it though.