function setup() {

  createCanvas(400, 400);

  stroke(255, 0, 0);

  background(220);

  for (let x = 0; x < width/2; x+=1) {

    for (let y = 0; y < height/2; y +=1) {

      // simple logic to change pixel color based on

      // x and y position

      if (x % 2 === 0) {

        stroke(0,0,255); 

      } else {

        stroke(255, 0, 0); 

      }

      point(x,y); 

    }

  }

}

​

function draw() {

​

}

​

​

​

​

​