int i = 0;
    int x = 10;
    int rectX, rectY;
    int rectSize = 25;
    int width =285;
    int height =285;

    color rectColor;
    boolean rectOver = false;

    //--//

    void setup() {
       size(600,600);
       background(0);

       rectColor = color(0);
       rectX = width/2-rectSize-10;
       rectY = height/2-rectSize/2;
    }

    void draw() {
      frameRate(5);
      for(int a = 15 ; a < 585 ; a = a + 20) {
        for(int i = 15 ; i < 585 ; i = i + 20) {
          fill(0,random(0,200),random(0,200));
          noStroke();
          rect(i,a,10,10);
        }
      }
      update(mouseX, mouseY);

      noStroke();
      if (rectOver) {
        background(rectColor);
      }
    }

    void update(int x, int y) {
      if ( overRect(rectX, rectY, rectSize, rectSize) ) {
        rectOver = true;
      }
    }

    boolean overRect(int x, int y, int width, int height) {
      if (mouseX >= x && mouseX <= x+width &&
          mouseY >= y && mouseY <= y+height) {
        return true;
          }
    }



    //╮( ˘_˘ )╭
    void mousePressed (){
      fill(random(0,200),0,random(0,200));
      redraw();
    }