The SuperTux game engine is structured as follows:
:*A Screen (screen.hpp) is the abstract base class for code that the MainLoop runs exclusively and full-screen.
Probably the most important Screen is the GameSession (game_session.cpp), which actually runs a Level (level.cpp).
Examples of other Screens are:
A GameSession loads and runs a single Level, which consists of multiple, separate parts, the Sectors. Sectors contain the various GameObjects that can be encountered in SuperTux.
Examples of such GameObjects are the Badguys, Players and TileMaps, but also Thunderstorm controllers, the currently visible viewport (i.e. a Camera object), the sector's time limit, etc.
More in-depth information about the game engine can be found in the source code itself, e.g. as Doxygen HTML Documentation, or on pages in :Category:Game Engine, most notably: