36 lines, no comments · 385 tokens, written in 3 seconds for $0.0033

 1  let circles = [];
 2  const NUM_CIRCLES = 20;
 3  
 4  function setup() {
 5    createCanvas(600, 400);
 6    for(let i=0; i<NUM_CIRCLES; i++) {
 7      circles.push({
 8        x: random(50, width-50),
 9        y: random(50, height-50),
10        r: random(15, 40),
11        dx: random(-3, 3),
12        dy: random(-3, 3),
13        c: color(random(255), random(255), random(255), 200)
14      });
15    }
16    noStroke();
17  }
18  
19  function draw() {
20    background(30, 30, 40, 100);
21    for(let i=0; i<circles.length; i++) {
22      let c = circles[i];
23      fill(c.c);
24      ellipse(c.x, c.y, c.r*2);
25      c.x += c.dx;
26      c.y += c.dy;
27      if (c.x - c.r < 0 || c.x + c.r > width) {
28        c.dx *= -1;
29        c.x = constrain(c.x, c.r, width-c.r);
30      }
31      if (c.y - c.r < 0 || c.y + c.r > height) {
32        c.dy *= -1;
33        c.y = constrain(c.y, c.r, height-c.r);
34      }
35    }
36  }