var letter = 'a'

​

function setup() {

  createCanvas(windowWidth, windowHeight)

  background(255)

  fill(0)

  textFont(font)

  textAlign(CENTER, CENTER)

}

​

function mouseDragged() {

  background(255, 80)

  stroke(0)

  noFill()

  textSize((mouseX - width/2) * 5)

  text(letter, width/2, mouseY)

}

​