let grid = [];

​

function setup() {

  createCanvas(400, 400);

  cols = width/size;

  rows = height/size;

  rectMode(CENTER);

  for (let i=0; i<cols; i++) {

    grid[i] = [];

    for (let j=0; j<rows; j++) {

      grid[i][j] = new Rect(size/2 + i*size, size/2 + j*size);

    }

  }

}

​

function draw() {

  background(220);

  let x = floor(mouseX / size);

  let y = floor(mouseY / size);

  for (let i=-1; i<2; i++) {

    for (let j=-1; j<2; j++) {

      let xIndex = x + i;

      let yIndex = y + j; 

      xIndex = constrain(xIndex, 0, cols-1);

      yIndex = constrain(yIndex, 0, rows-1);

      grid[xIndex][yIndex].display();

      grid[xIndex][yIndex].life = 255;

    }

  }

}

​

​