final int W = 400; final int H = 400;
float x = W/2;     float y = H/2;
int i = 0;         boolean down = true;
final float pi = 3.14;   final float pi2 = 6.28;
float dir = 0;
void setup(){
  size( W, H );
  strokeWeight(2);
  background( #000000 );
}
void rt(float angle){
  dir = dir-angle/180*pi; if (dir < 0) dir = dir + pi2;
}
void lt(float angle){
  dir = dir+angle/180*pi; if (dir > 2*pi) dir = dir - pi2;
}
void fwd(float d){
  float u = x+d*cos(dir); float v = y +d*sin(dir);
  if (down) line( u, v, x, y );
  x = u; y = v;
}
public void draw(){
  stroke( (i*i+127)%255, 0, (i+127)%255, i%31 );
  fwd(i/5); lt(i/5);
  if (i < 1000) i++; else noLoop();
}