code: function fillMatrix(id, t, l, w, h) {
                  for (var y = t; y < t + h;) {
                      for (var x = l; x < l + w;) {
                          matrix[y + '-' + x] = id;
                          ++x > maxX && (maxX = x);
                      }
                      ++y > maxY && (maxY = y);
                  }
              }
docs: fill area with top, left, width, height;