SketchBook

var N = 1;
var bump = 3;
var speed = 0.001;
var span = 3;
var SIZE = 300;

function setup() {
createCanvas(SIZE, SIZE);
noStroke();
}

var centerX = SIZE / 2;
var centerY = SIZE / 2;
var change_diameter = SIZE / (bump * N);
var change_centerX;

function draw() {
background(238, 238, 238);
draw_circles();
}

function draw_circles() {
var dia = SIZE;
var flag = 0;

centerX = SIZE / 2;
centerY = SIZE / 2;
change_centerX = span;

for (var n = 0; n < bump; n++) {
for (var i = 0; i < N; i++) {
fill(25) * (flag);
ellipse(centerY + (width / 2 - centerX) * cos(speed * millis()), centerY, dia);
dia -= change_diameter;
centerX += change_centerX;
flag = !flag;
}
change_centerX = -change_centerX;
}
}