  A new window to observing individual stars and other small sources at
cosmological distances was opened recently, with the detection of several
caustic-crossing events in galaxy cluster fields. Many more such events are
expected soon from dedicated campaigns with the \emph{Hubble Space Telescope}
and from the \emph{James Webb Space Telescope}. These events can teach us not
only about the lensed sources themselves, such as individual high-redshift
stars, star clusters, or accretion disks, but through their light-curves they
also hold information about the point-mass function of the lens and thus,
potentially, the composition of dark matter. We present here a simple method
for simulating light curves of such events, i.e., the change in apparent
magnitude of the source as it sweeps over the net of caustics generated by
microlenses embedded around the critical region of the lens. The method is
recursive and so any reasonably sized small source can be accommodated, down to
sub-solar scales, in principle. We compare the method, which we dub
\emph{Adaptive Boundary Method}, with other common methods such as simple
inverse ray shooting, and demonstrate that it is significantly more efficient
and accurate in the small-source and high-magnification regime of interest. A
\textsc{python} version of the code is made publicly available in an
open-source fashion for simulating future events.
