var a = 0;

var bg = true;

​

function setup() { 

  createCanvas(600, 400);

  background(255);

} 

​

function draw() { 

  d=random(20,60);

  a = map(mouseX,0,width,40,120);

  // a=random(40,120);

  noStroke ();

  fill(random(0,255),0,random(100,255),a);

  ellipse(random(width),random(height),d,d);

}

​

function mousePressed() {

    bg=!bg;

    if (bg == false) {

    background(0); 

  } else { 

    background(255);

  }

}

​

​