code: function fillFinders(matrix) {
      var N = matrix.length;
      for (var i = -3; i <= 3; i++) {
          for (var j = -3; j <= 3; j++) {
              var max = Math.max(i, j);
              var min = Math.min(i, j);
              var pixel = (max == 2 && min >= -2) || (min == -2 && max <= 2) ? 0x80 : 0x81;
              matrix[3 + i][3 + j] = pixel;
              matrix[3 + i][N - 4 + j] = pixel;
              matrix[N - 4 + i][3 + j] = pixel;
          }
      }
      for (var i = 0; i < 8; i++) {
          matrix[7][i] = matrix[i][7] =
          matrix[7][N - i - 1] = matrix[i][N - 8] =
          matrix[N - 8][i] = matrix[N - 1 - i][7] = 0x80;
      }
  }
docs: {{{1 Put finders into matrix