Managing game state / 'what to update' within an XNA game 'screen'
- by codinghands
Note - having read through other GDev questions suggested when writing this question I'm confident this isn't a dupe. Of course, it's 3am and I'm likely wrong, so please mod as such if so.
I'm trying to figure out how best to manage state within my game screens - please bare with me though! At the moment I'm using a heavily modified version of the fantastic game state management example on the XNA site available here. This is working perfectly for my 'Screens' - 'IntroScreen' with some shiny logos, 'TitleScreen' and a 'MenuScreen' stacked on top for the title and menu, 'PlayScreen' for the actual gameplay, etc. Each screen has the a bunch of sprites, and an 'Update' and 'Draw', managed by a 'ScreenManager'.
In addition to the above, and as suggested as an answer to my other question here, most screens have a 'GameProcessQueue' class full of 'GameProcess'es which lets me do just about anything (animations, youbetcha!), in any order, in sequence or parallel.
Why mention all this? When I talk about managing game state I'm thinking more for complex scenarios within a 'Screen'. 'TitleScreen', 'MenuScreen' and the like are all relatively simple. 'Play Screen' less so. How do people manage the different 'states' within the screen (or whatever you call it) that 'does' gameplay? (for me, the 'PlayScreen')
I've thought about the following:
Enum of different states in the Screen, 'activeState' enum-type
variable, switching on the enum in the Screen Update() loop to
determine what Screen Update 'sub'-function is called. I can see this getting hairy pretty fast though as screens get more complex and with the 'PlayScreen' becoming a behemoth mega-class.
'State' class with Update loop - a Screen can have any number of 'States', 1+ of which are 'active'. Screen update loop calls update on all active states. States themselves know which screen they belong to, and may even belong to a 'StateManager' which handles transitioning from one state to the next. Once a state is over it's removed from the ScreenState list. The Screen doesn't need a bunch of GameProcessQueues, each State has its own.
Abstract Screen further to be more flexible - I can see the similarities between what I've got (game 'Screens' handled by a ScreenManager) and what I want (states within a screen, and a mechanism to manage them). However at the moment I see 'Screens' as high level and very distinct ('PlayScreen' with baddies != 'MenuScreen' with 4 words and event handlers), where as my proposed 'States' are more intrinsically tied to a specific screen with complex requirements. I think.
This is for a turn-based board game, so it's easier to define things as a discrete series of steps (IntroAnimation - P1Turn - P2Turn - P1Turn ... - GameOver - .... Obviously with an open-world RPG things are very different, but any advice in this scenario is appreciated.
If I'm just going OOP-crazy please say so. Similarly I'm concious there's a huge amount on this site re: state management. But as my first 'serious' game after a couple of false starts I'd like to get this right, and would rather be harassed and modded down than never ask :)
