void setup(){
  size(600,400);
  background(255);
  stroke(255,0,0);
  garis(400,100,200,100);
  garis(400,100,400,200);
  garis(200,100,200,200);
  garis(200,200,400,200);
}

void garis(int xAwal,int yAwal, int xAkhir,int yAkhir){
  float x = xAwal;
  float y = yAwal;
  float dX=xAkhir-xAwal;
  float dY=yAkhir-yAwal;
  float k;

   if(abs(dX)>=abs(dY)){
    k=abs(dX);
  }else{
    k=abs(dY);
  }
  point(x,y);
  for(int i=1;i<=k;i++){
  x=(dX/k)+x;
  y=(dY/k)+y;
  point(x,y);
}
}