  Graphene has proven to host outstanding mesoscopic effects involving massless
Dirac quasiparticles travelling ballistically resulting in the current flow
exhibiting light-like behaviour. A new branch of 2D electronics inspired by the
standard principles of optics is rapidly evolving, calling for a deeper
understanding of transport in large-scale devices at a quantum level. Here we
perform large-scale quantum transport calculations based on a tight-binding
model of graphene and the non-equilibrium Green's function method and include
the effects of $p-n$ junctions of different shape, magnetic field, and
absorptive regions acting as drains for current. We stress the importance of
choosing absorbing boundary conditions in the calculations to correctly capture
how current flows in the limit of infinite devices. As a specific application
we present a fully quantum-mechanical framework for the "2D Dirac fermion
microscope" recently proposed by B{\o}ggild $et\, al.$ [Nat. Comm. 8, 10.1038
(2017)], tackling several key electron-optical effects therein predicted via
semiclassical trajectory simulations, such as electron beam collimation,
deflection and scattering off Veselago dots. Our results confirm that a
semiclassical approach to a large extend is sufficient to capture the main
transport features in the mesoscopic limit and the optical regime, but also
that a richer electron-optical landscape is to be expected when coherence or
other purely quantum effects are accounted for in the simulations.
