Document Game Start Process Order

[jdrueckert]

Documentation Topic

In StateLoading.java I noticed some discrepancies in the process loading order between client and host.
I don't think this topic is well-documented yet or at least I'm not aware of any such documentation.

Major question for me also is: is the difference in order intentional or a bug?

Documentation Type

With this being architectural documentation of sorts but heavily coupled with the code (despite probably being not modified too often), I would recommend this being documented in the Terasology Engine wiki or in-repo docsify to allow for documentation update as part of related code changes.

If these differences in order of loading are indeed intentional, then this should potentially also be documented in a code comment to avoid future confusion.

Additional notes

The order of process loading for client and host is generally equal (+/- some host only processes and processes that come in dedicated client or host flavours) save for

• LoadExtraBlockData (which is done later on host side than on client side) and
• RegisterBlockFamilies (which is done a lot later on client side than on host side)

Step	Client	Host
1	JoinServer (clients only)	RegisterMods (host only)
2	InitialiseRendering*	InitialiseRendering*
3	InitialiseEntitySystem	InitialiseEntitySystem
4	RegisterBlocks	RegisterBlocks
5	InitialiseGraphics*	InitialiseGraphics*
6	LoadPrefabs	LoadPrefabs
7	ProcessBlockPrefabs	ProcessBlockPrefabs
8	LoadExtraBlockData	-
9	InitialiseComponentSystemManager	InitialiseComponentSystemManager
10	RegisterInputSystem*	RegisterInputSystem*
11	RegisterSystems	RegisterSystems
12	InitialiseCommandSystem	InitialiseCommandSystem
13	-	LoadExtraBlockData
14	InitialiseRemoteWorld (clients variant)	InitialiseWorld (host variant)
15	-	RegisterBlockFamilies
16	-	EnsureSaveGameConsistency (host only)
17	InitialisePhysics	InitialisePhysics
18	InitialiseSystems	InitialiseSystems
19	PreBeginSystems	PreBeginSystems
20	-	LoadEntities (host only)
21	-	InitialiseBlockTypeEntities (host only)
22	CreateRemoteWorldEntity (client variant)	CreateWorldEntity (host variant)
23	-	InitialiseWorldGenerator (host only)
24	-	InitialiseRecordAndReplay (host only)
25	-	Start Server (server only)
26	PostBeginSystems	PostBeginSystems
27	SetupRemotePlayer (client variant)	SetupLocalPlayer (host variant if local player)
28	AwaitCharacterSpawn	AwaitCharacterSpawn
29	RegisterBlockFamilies	-
30	PrepareWorld	PrepareWorld

* only if not in headless mode

While we're at it we might also want to document the different execution modes (client only, host but not server, host and server, host with local player, etc.)
E.g., a singleplayer game is actually a host, as is a server game. only clients in a multiplayer setup are actually clients (see logic in stateloading.java and newgamescreen.java)