plot.html

<input id=I value=z=y/x*9><p><canvas id=a width=500 height=500>
<script>
c=a.getContext`2d`;
var P = [];
var w = 0;
if(location.hash)I.value=atob(location.hash.slice(1));
setInterval(e=>{
  a.width ^= 0;
  w += .01;
  for(X = 38; X--;){
    P[X] = [];
    for(Y = 38; Y--;){
      x = X * 5 - 90;
      y = Y * 5 - 90;
      eval(I.value);
      p=Math.atan2(y,x)-w;
      d=Math.hypot(y,x);
      x=Math.sin(p)*d;
      y=Math.cos(p)*d;
      p=Math.atan2(y,z)+1;
      d=Math.hypot(y,z);
      z=Math.sin(p)*d;
      y=Math.cos(p)*d;
      y+=250;
      P[X][Y] = [250+x/y*250, 250+z/y*250];
      c.moveTo(P[X][Y][0], P[X][Y][1]);
      try{c.lineTo(P[X][Y+1][0], P[X][Y+1][1])}catch(e){};
      c.moveTo(P[X][Y][0], P[X][Y][1]);
      try{c.lineTo(P[X+1][Y][0], P[X+1][Y][1])}catch(e){};
    }
  }
  c.stroke();
  location.hash=btoa(I.value);
}, 33);
</script>