This was done to ensure that this code only runs when the thinker itself is fully set up.
With a constructor there is no control about such things, if some common initialization needs to be done it has to be in the base constructor, but that makes the entire approach chosen here to ensure proper linking into the thinker chains impossible.
ZDoom originally did it that way, which resulted in a very inflexible system and required some awful hacks to let the serializer work with it - the corresponding bSerialOverride flag is now gone.
The only thinker class still having a constructor is DFraggleThinker, because it contains non-serializable data that needs to be initialized in a piece of code that always runs, regardless of whether the object is created explicitly or from a savegame.
This doesn't really write out any info for the pointer, if the level does not match it just errors out.
This is both for quick detection of badly used level data and for automatic restoring of the pointer from the serializer's working level.
This also removed the temporary workarounds in DAutomap and DLevelScript to restore these pointers when a savegame is loaded.
UI always runs on the primary level, so this does not need the ability to operate on multiple levels. Additionally, this can later be set to null when running play code so that scope violations result in an abort.
This also changes the action special interface to pass a Level parameter to the separate functions and makes a few other minor adjustments to the polyobject code.
This caused bad calculations with CMF_OFFSETPITCH. Note that to compensate for the fix, the SphericalCoords function had to have its own inversion of the value removed so that it calculates the same result as before.
There are several places where a temporary change of light mode is needed, all these made this change in the global level struct. Now the change is only local to the active draw info.
I have to wonder why it had to use such a complicated implementation that provided no advantages whatsoever.
The new code is just 1/5th of the old one's size and much closer to Hexen's original implementation which also was a simple array but with no means to resize the queue.
This involves passing the level explicitly to many functions. What was done here may seem a bit excessive but at least it covers everything.
Most importantly, the global ActiveThinker pointer has been moved into FLevelLocals and is now getting tracked properly by the level without using dangerous assumptions about how the game organizes its data.
Unlike the other classes, the places where variables from this class were accessed were quite scattered so there isn't much scriptified code. Instead, most of these places are now using the script variable access methods.
This was the last remaining subclass of AActor, meaning that class Actor can now be opened for user-side extensions.
Since these can be changed on the placed light actor they have to be read from there, so this is now a pointer in FDynamicLight, just like the other properties that can be user-changed.
Also did some cleanup on the interface so that external code doesn't need to dereference the lightflags pointer but can use utility functions for all flags.
This did no longer sort sprites in the same position reliably since the feature to render sprites which only partially are inside a sector was added.
With this, sprites in the same position are no longer guaranteed to be added to the render list in sequence.
Fixed by adding an 'order' field to AActor which gets incremented with each spawned actor and reset when a new level is started.
The software renderer will also need a variation of this fix but its data no longer has access to the defining actor when being sorted, so a bit more work is needed here.
* it was never saved in savegames, leaving the state of dead bodies undefined
* it shouldn't be subjected to pointer substitution because all it contains is old dead bodies, not live ones.
Game crashed when any of gl_brightfog, gl_lightadditivesurfaces, gl_notexturefill CVARs is set with no level loaded
There was impossible to reset settings to defaults because of this
