var end = 0;

function setup() {

  createCanvas(400, 400);

  noStroke();

}

​

function draw() {

  background(220);

  fill(255,0,0);

  if ((mouseX<=width/3) && ((mouseY<=height)&&(mouseY>=0))){

    if (end != 0) {

        rectPressed[0] = false;

    }

    end = 0;

  } else if ((mouseX<=width*2/3) && ((mouseY<=height)&&(mouseY>=0))){

    if (end != 1) {

        rectPressed[1] = false;

    }

    end = 1;

  } else if ((mouseX<=width) && ((mouseY<=height)&&(mouseY>=0))) {

    if (end != 2) {

        rectPressed[2] = false;

    }

    end = 2;

  } else {

    end = 4;

  }

  if (rectPressed[0]){

    rect(0,0,width/3,height);

  }

  if (rectPressed[1]){

    rect(width/3,0,width/3,height);

  }

  if (rectPressed[2]){

    rect(width*2/3,0,width,height);

  }

}

​

function mousePressed(){

  if ((mouseX<=width/3) && ((mouseY<=height)&&(mouseY>=0))) {

    rectPressed[0] = true;

  } else if ((mouseX<=width*2/3) && ((mouseY<=height)&&(mouseY>=0))){

    rectPressed[1] = true;

  } else if ((mouseX<=width) && ((mouseY<=height)&&(mouseY>=0))){

    rectPressed[2] = true;

  }

}