function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  // Draw an ellipse at the center of the screen.

  // Relate the width and height of the ellipse to mouseX.

  // There is a positive relationship between mouseX and the width of the ellipse. As mouseX increases, so does the width.

  // There is a negative relationship between the mouseX and the height of the ellipse. As mouseX increases, the height decreases.

  ellipse(width/2, height/2, mouseX, 400-mouseX);

}