​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  //square(0,0,100)

  //square(100,0,100)

  //square(200,0,100)

  //square(300,0,100)

  blockSize = constrain(mouseX,4,width);

  for (let x=0; x<width; x+=blockSize){

    square(x,0,blockSize)

  }

}