  The shadow-complexity is an invariant of closed $4$-manifolds defined by
using $2$-dimensional polyhedra called Turaev's shadows, which, roughly
speaking, measures how complicated a $2$-skeleton of the $4$-manifold is. In
this paper, we define a new version $\mathrm{sc}_{r}$ of shadow-complexity
depending on an extra parameter $r\geq0$, and we investigate the relationship
between this complexity and the trisection genus $g$. More explicitly, we prove
an inequality $g(W) \leq 2+2\mathrm{sc}_{r}(W)$ for any closed $4$-manifold $W$
and any $r\geq1/2$. Moreover, we determine the exact values of
$\mathrm{sc}_{1/2}$ for infinitely many $4$-manifolds, and also we classify all
the closed $4$-manifolds with $\mathrm{sc}_{1/2}\leq1/2$.
