const numCols = 6;

const boxPadding = 8;

​

let boxWidth;

let boxHeight;

​

function setup() {

  createCanvas(400, 400);

​

  boxWidth   = (width - ((numCols + 1) * boxPadding))/ numCols;

  boxHeight  = (height - ((numRows + 1) * boxPadding)) / numRows;

}

​

function draw() {

  background(120);

  renderGrid();

}

​

function renderGrid(){

  for(let i = 0; i < numRows; i++){

    for(let j = 0; j < numCols; j++){

      rect( getX(j), getY(i), boxWidth, boxHeight);

    }

  }

}

function getX(colIndex){

  return colIndex * boxWidth + boxPadding + colIndex * boxPadding;

}

function getY(rowIndex){

  return rowIndex * boxHeight + boxPadding + rowIndex * boxPadding;

}

​