  Two-dimensional simulations are used to explore topological transitions that
occur during the formation of films grown from grains that are seeded on
substrates. This is done for a relatively large range of the initial value
$\Phi_s$ of the grain surface fraction $\Phi$. The morphology of porous films
is captured at the transition when grains connect to form a one-component
network using newly developed raster-free algorithms that combine computational
geometry and network theory. Further insight on the morphology of porous films
and their suspended counterparts is obtained by studying the pore surface
fraction $\Phi_p$, the pore over grain ratio, the pore area distribution, and
the contribution of pores of certain chosen areas to $\Phi_p$. Pinhole survival
is evaluated at the transition when film closure occurs using survival function
estimates. The morphology of closed films ($\Phi = 1$) is also characterized
and is quantified by measuring grain areas and perimeters. The majority of
investigated quantities are found to depend sensitively on $\Phi_s$ and the
long-time persistence of pinholes exhibits critical behavior as a function of
$\Phi_s$. In addition to providing guidelines for designing effective processes
for manufacturing thin films and suspended porous films with tailored
properties, this work may advance the understanding of continuum percolation
theory.
