Added description of simultaneous turns functionality to player docs

docs/players/Game_Mechanics.md

@@ -144,7 +144,7 @@ It's the new feature meant for testing game performance on various platforms.
 
 Additional color are supported for text fields (e.g. map description). Uses HTML color syntax (e.g. #abcdef) / HTML predefined colors (e.g. green).
 
-##### Original Heroes III Support
+### Original Heroes III Support
 
 `This is white`
 
@@ -154,7 +154,7 @@ Additional color are supported for text fields (e.g. map description). Uses HTML
 
 <span style="color:yellow;background-color:black;">This is yellow</span>
 
-##### New
+### New
 
 `{#ff0000|This is red}`
 
@@ -164,6 +164,41 @@ Additional color are supported for text fields (e.g. map description). Uses HTML
 
 <span style="color:green">This is green</span>
 
+# Multiplayer
+
+Opening new Turn Option menu in scenario selection dialog allows detailed configuration of turn timers and simultaneous turns
+
+## Turn Timers
+
+TODO
+
+## Simultaneous turns
+
+Simultaneous turns allow multiple players to act at the same time, speeding up early game phase in multiplayer games. During this phase if different players (allies or not) attempt to interact with each other, such as capture objects owned by other players (mines, dwellings, towns) or attack their heroes, game will block such actions. Interaction with same map objects at the same time, such as attacking same wandering monster is also blocked.
+
+Following options can be used to configure simultaneous turns:
+- Minimal duration (at least for): this is duration during which simultaneous turns will run unconditionally. Until specified number of days have passed, simultaneous turns will never break and game will not attempt to detect contacts.
+- Maximal duration (at most for): this is duration after which simultaneous turns will end unconditionally, even if players still have not contacted each other. However if contact detection discovers contact between two players, simultaneous turns between them might end before specified duration.
+- Simultaneous turns for AI: If this option is on, AI can act at the same time as human players. Note that AI shares settings for simultaneous turns with human players - if no simultaneous turns have been set up this option has no effect.
+
+### Contact detection
+
+While simultaneous turns are active, VCMI tracks contacts for each pair of player separately.
+
+Players are considered to be "in contact" if movement range of their heroes at the start of turn overlaps, or, in other words - if their heroes can meet on this turn if both walk towards each other. When calculating movement range, game uses same rules as standard movement range calculation in vcmi, meaning that game will track movement through monoliths and subterranean gates, but will not account for any removable obstacles, such as wandering monsters or treasures that block path between heroes. At the moment, game will not account for any ways to extend movement range - Dimension Door or Town Portal spells, visiting map objects such as Stables, releasing heroes from prisons, etc.
+
+Once detected, contact can never be "lost". If game detected contact between two players, this contact will remain active till the end of the game, even if their heroes move far enough from each other.
+
+Game performs contact detection once per turn, at the very start of each in-game day. Once contact detection has been performed, players that are not in contact with each other can start making turn. For example, in game with 4 players: red, blue, brown and green. If game detected contact between red and blue following will happen:
+- red, brown and green will all instantly start turn
+- once red ends his turn, blue will be able to start his own turn (even if brown or green are still making turn)
+
+Once maximal duration of simultaneous turns (as specified during scenario setup) has been reached, or if all players are in contact with each other, game will return to standard turn order: red, blue, brown, green...
+
+### Differences compared to HD Mod version
+
+- In VCMI, players can see actions of other players immediately (provided that they have revealed fog of war) instead of waiting for next turn
+- In VCMI, attempt to attack hero of another player during simultaneous turns will be blocked instead of reloading save from start of turn like in HD Mod
 
 # Manuals and guides