float x1,y1,x2,y2;
float x3,y3;

size(300,300);
x1=100;
y1=200;

x2=250;
y2=300;

line(x1,y1, x2,y2);
line(0,0, x1,y1);
line(0,0, x2,y2);

rectMode(CENTER_DIAMETER);
rect(x1,y1, 20,20);
rect(x2,y2, 20,20);