​

let x = 50;

 let speed = 1;

​

 function setup() {

   createCanvas(400, 400);

   textAlign(CENTER, CENTER);

​

 }

​

 function draw() {

​

   background(0);

   strokeWeight(1);

   stroke(100);

   noFill();

   ellipse(50, 200, 100, 100);

   ellipse(350, 200, 100, 100);

   stroke(255);

   strokeWeight(2);

   ellipse(x, 200, 100, 100);

​

   noStroke();

   fill(100);

   text("keyframe A", 50, 200);

   text("keyframe B", 350, 200);

​

   x = x + speed;

​

   if (x > width - 50) {

     speed = -1;

   } else if (x == 50) {

     speed = 1;

   }

​

 }