function getAdjacentArrayBounds(pointer, spread, length) {
        return [
            // Math.max(0, pointer - spread),
            Math.max(0, pointer),
            Math.min(length - 1, pointer + spread)
        ]
    }
[getAdjacentArrayBounds retuns existing adjacent lower and upper column bounds]
@param  {[int]} pointer [current index]
@param  {[int]} spread  [distance from index]
@param  {[int]} length     [total length]
@return {[array]}         [0] lower bound, [1] upper bound