Editing Hexen: Beyond Heretic (section)

===Engine modifications===
"Polyobjects" are the walls that move within the game. Because the ''Doom'' engine uses the [[binary space partitioning]] system for rendering, it does not enable moving walls. ''Hexen''{{'}}s moving walls are actually one-sided lines built somewhere else on the map and rendered at the desired start spot when the level is loaded. This enables a pseudo-moving wall, but does not allow moving sectors (such as seeing the tops of moving doors). This often creates problems in sectors containing more than one node, however, explaining the relatively limited use of polyobjects.

Whereas ''Doom'', ''Doom II'', and ''Heretic'' rely on lines within the maps to perform simple actions, ''Hexen'' also allows these actions to be activated by Action Code Script (ACS). These scripts use a syntactic variant of [[C (programming language)|C]], thus allowing special sequencing of game actions. Programming features such as randomization, variables, and intermap script activation enable smooth hub gameplay and are responsible for most of the special effects within the game: on-screen messages, random sound effects, monster spawning, sidedef texture changes, versatile control of polyobjects, level initialization for deathmatch, and even complex environment changes such as earthquakes manipulating floor textures and heights.