​

let left, right, upper, bottom

​

function setup() {

  createCanvas(800, 400);

  left= width/4;

  right= 3/4 * width;

  upper= height/4;

  bottom= 3/4 * height

  upperLeftX= left ;

  upperLeftY= upper;

  upperRightX= right;

  upperRightY= upper;

  bottomRightx= right;

  bottomRightY= bottom ;

  bottomLeftX= left;

  bottomLeftY= bottom;

}

​

function draw() {

  background(220);  

  line(upperLeftX, upperLeftY, upperRightX, upperRightY );

  line(upperRightX, upperRightY, bottomRightx, bottomRightY );

  line(bottomRightx, bottomRightY , bottomLeftX, bottomLeftY );

  line(bottomLeftX, bottomLeftY, upperLeftX, upperLeftY);

}