Serious Sam

Croteam created a proprietary engine for use in both Serious Sam: The First Encounter and Serious Sam: The Second Encounter. At the time Croteam was making Serious Sam, licensing other engines was costly (upwards of US$1 million), so they made their own from scratch, following the feature set of the first Doom engine, which simulated 3D spaces in 2D, and did not include up or down targeting. As they were creating their own, both Duke Nukem 3D (which added up-and-down freelook) and Quake (a fully 3D rendered environment) were released, requiring Croteam to incorporate these features into their engine for their game to be competitive. Development was further complicated when the first 3D accelerators were released, prompting Croteam to develop for hardware rendering over software.

Recognizing they needed to bring something new to what other games were pushing at that time, Croteam decided that they would make their Serious Engine support extremely large environments, with virtual view distances of over a kilometre, physics support, and capability of rendering up to a hundred enemies on screen at a time, and do this on the processing power of what current low-end computers using the original Pentium CPUs could handle. The team devised ways of doing object path caching so that they only had to perform collision detection with environmental features every few seconds rather than every cycle. Collision detection was also sped up by approximating the environment with spheres rather than boxes. This also enabled them to have multidirection gravity which was used for some of the game's secret areas.