Two link mainpulator

i`m working in a project to design to link arm that writes letters or
draws some simple figure(sqaure,traingle).i obtained the inverse
kinematic and simulated the mechanasim in mathlab.I could draw cicrle
my question is how i can modify my program to draw a suqaure or
trianlge or even letters?
this is the mathlab code:

clear all
close all
clc
clear
t=0:0.1:2*pi;
r=1; //raduis of the cicle
n=length(t);
l1=1;
l2=1;

for i=1:n;
  x(i)=r*cos(t(i));
  y(i)=r*sin(t(i));

    c2=(x(i)^2+y(i)^2-l1^2-l2^2)/(2*l1*l2);
    s2=sqrt(1-c2^2);
    th2(i)=atan2(s2,c2)
    k1=l1+l2*c2;
    k2=l2*s2;
    th1(i)=atan2(y(i),x(i))-atan2(k1,k2)
    x1=l1*cos(th1(i));
    y1=l1*sin(th1(i));
    x2=x1+l2*cos(th1(i)+th2(i));
    y2=y1+l2*sin(th1(i)+th2(i));
    line([0,x1,x2],[0,y1,y2]);hold on;pause(0.5);
    
 
end;