Motor control for line drawing with scara

Hello

I am forth year computer engineering student and working on NXT scara robot for my graduation project.

I coded Matlab program which makes image process from the webcam taken photo and creates x y coordinates of lines as a matrices and I would like to send that lines to NXT to draw but I have some difficulties to understand how to do that. The question is how to program motors for these coordinates. I know that I need to use inverse kinematics and I know how to learn the theta angles of joints. The motor controller works with that theta angles but how will I make the lines continuous? I need some guiding and suggestions...

Best regards