This variable can be used to emulate the behavior of prior engine versions
for compatibility reasons.
5 - IGNORE_PASSABLE won't ignore passable map entities, as in A7.10 or earlier.
Don't load sun_color and ambient_color from a level, as in A7.20 or earlier.
Don't use the primary monitor, but a hypothetical 4:3 monitor as reference for view.aspect, as in A7.60 or earlier.
File functions open files in the SAVEDIR rather than the work folder, as in A.66 or earlier.
c_setminmax does not use the entity scale and frames, as required for the A6 templates.
Render targets bigger than the screen are reduced to screen size, as in A7.82 or earlier.
Lightmaps in models with more than 3 skins are not detected and don't affect entSkin2, as in A7.84 or earlier.
Video memory is indicated in KB, not MB, as in 8.10 or earlier.
compatibilty = 6; // behave like version 7.20; keep sun_color and ambient_color at their default settings