  Given a simple polygon $ \mathcal {P} $ of $ n $ vertices in the Plane. We
study the problem of computing the visibility area from a given viewpoint $ q $
inside $ \mathcal {P} $ where only sub-linear variables are allowed for working
space. Without any memory-constrained, this problem was previously solved in $
O(n) $-time and $ O(n) $-variables space. In a newer research, the visibility
area of a point be computed in $ O(n) $-time, using $ O(\sqrt{n}) $ variables
for working space. In this paper, we present an optimal-time algorithm, using $
O(c/\log n) $ variables space for computing visibility area, where $ c<n $ is
the number of critical vertices. We keep the algorithm in the linear-time and
reduce space as much as possible.
