  Thanks to Pfaffian techniques, we study the R\'enyi entanglement entropies
and the entanglement spectrum of large subsystems for two-dimensional
Rokhsar-Kivelson wave functions constructed from a dimer model on the
triangular lattice. By including a fugacity $t$ on some suitable bonds, one
interpolates between the triangular lattice (t=1) and the square lattice (t=0).
The wave function is known to be a massive $\mathbb Z_2$ topological liquid for
$t>0$ whereas it is a gapless critical state at t=0. We mainly consider two
geometries for the subsystem: that of a semi-infinite cylinder, and the
disk-like setup proposed by Kitaev and Preskill [Phys. Rev. Lett. 96, 110404
(2006)]. In the cylinder case, the entropies contain an extensive term --
proportional to the length of the boundary -- and a universal sub-leading
constant $s_n(t)$. Fitting these cylinder data (up to a perimeter of L=32
sites) provides $s_n$ with a very high numerical accuracy ($10^{-9}$ at t=1 and
$10^{-6}$ at $t=0.5$). In the topological $\mathbb{Z}_2$ liquid phase we find
$s_n(t>0)=-\ln 2$, independent of the fugacity $t$ and the R\'enyi parameter
$n$. At t=0 we recover a previously known result, $s_n(t=0)=-(1/2)\ln(n)/(n-1)$
for $n<1$ and $s_n(t=0)=-\ln(2)/(n-1)$ for $n>1$. In the disk-like geometry --
designed to get rid of the boundary contributions -- we find an entropy $s^{\rm
KP}_n(t>0)=-\ln 2$ in the whole massive phase whatever $n>0$, in agreement with
the result of Flammia {\it et al.} [Phys. Rev. Lett. 103, 261601 (2009)]. Some
results for the gapless limit $R^{\rm KP}_n(t\to 0)$ are discussed.
