Rain simulations in video games and other real-time applications can be used to enhance the atmosphere of immersive titles, immersing the audience in a believable simulacrum of a seemingly commonplace event. Most existing sources use several layers of effects to convincingly fake the effect of rain, resulting in an experience which appears seamless initially, but falls apart under scrutiny. These methods tend to rely on the quality of each individual effect to hide the seams at first glance, long enough that most viewers could move on without the problems becoming apparent. The Real Time Rain Simulation (RTRS) is meant as a proof of concept for a simplified physical simulation of rain falling against a window and aims to be extensible, able include a wide variety of effects with minimal effort.