Computer simulations typically determine the particle-distribution function corresponding to a single-event point source. This distribution function contains all the information needed to determine the corresonding steady-state distribution. From the single-event point-source distribution one can also deduce the distributions resulting from plane and volume-homogeneous sources, both for single event and steady state. A formalism for making these deductions is developed, based on the observation that the distribution determined by computer simulation obeys the Boltzmann transport equation, and on the properties of the Green's functions solutions of that equation, particularly the consequences of space- and time-translation invariance. The treatment deals explicitly with a homogeneous target infinite in every direction, but is easily generalized to cases with boundary conditions, such as a beam bombarding a layered target in slab geometry.