let spotA;

let spots = [];

​

function setup() {

  createCanvas(1920, 1080);

  //Initial spot size and alpha 

  spotSize = 240;

  spotA = 200;

}

​

function draw() {

  background(255);

  fill(0);

  circle(width/2,height/2,height);

  noFill();

  stroke(255);

  strokeWeight(5);

  ellipse(mouseX, mouseY, spotSize);

  for (let s of spots){

    s.drop();

    s.disappear();

  }

  //Clean up old spots in the array

  if (spots.length > 50) {

    spots.splice(0, 1);

  }

}

​

​

​

function mousePressed(){

  let spot = new Spot(mouseX, mouseY);

  spots.push(spot);

}

​

​

​

class Spot {

  constructor(x,y) {

    this.x = x;

    this.y = y;

    this.size = spotSize;

    this.a = spotA;

  }

  drop(){

    noStroke();

    fill(255, this.a);

    ellipse(this.x, this.y, this.size);

  }

  disappear(){

    this.size -= 0.08;  //how fast spots shrink

    this.a -= 0.2;     //how fast spots fade

    this.size = constrain(this.size, 0, this.size);

    this.a = constrain(this.a, 0, this.a);

  }

}