parallelparabola

c = 0;a = 0.5;x = -20;y = 400;
function setup() {
  createCanvas(400, 400);
  frameRate(15);
  background(0)
  stroke(255)
}
function draw() {
  translate(200,200)//set origin (0,0)
  for (let i=-21;i<22;i=i+0.05){
    t = i;
    oldx = x;
    oldy = y;
    x = 2*a*t+c*t/sqrt(1+pow(t,2));
    y = a*pow(t,2)-c/sqrt(1+pow(t,2));
    if (i >-40){
      line(x,y,oldx,oldy)
    }
  }
  c =c+5;
  x = -20;
  y = 400;
  stroke(255-c/1.1)
  circle(0,200-c,2)
  if (c>200){
    fill(0,0,0,5);
    circle(0,0,c/2.5)
    print(c)
  }
  if (c>1250){
    background(0);
    c = 0;
  }
  
}