Gameloop for j2me "turn-based" game

Question

Edit: This makes alot more sense to me now that i've taken a step away from the code, thanks for the help.

Just found stack overflow the other day through Coding Horror and it looks awesome. Figure that i'd ask the community about a problem i'm currently trying to work out.

I'm developing a roguelike sortof game using j2me for midp 2.0 phones. The project is still in the basic stages of development as I figure out how it's going to work. The part i'm currently stuck on has to do with threading.

The game has a custom HaxCanvas class which extends GameCanvas and Implements runnable. It's run method calls repaint() and then sleeps for 50 ms, resulting in a frame rate of 20 FPS. This allows me to write the rest of the game without having to put repaint everywhere and should make animations and effects easier to do later on. (at least in theory).

The flow of the game is controlled by a GameManager class, which loops through all the NPC's on the map, taking their turns, until it's the player's turn. At this point I need to get input to allow the player to move around and/or attack things. I originally was calling gameManager.runUntilHeroTurn() in the keyPressed method of my HaxCanvas. However after reading up on j2me system threads I realized that putting a method with the potential to run for a while in a callback is a bad idea. However I must used keyPressed to do input handeling, since i need access to the number keys, and getKeyStates() does not support this.

Sofar my attempts to put my gameloop in it's own thread have resulted in disaster. A strange "uncaught ArrayIndexOutOfBoundsException" with no stack trace shows up after the game has run for several turns .

So i suppose my question is this:

For a "turn based" game in j2me, what's the best way to implement the game loop, allowing for input handeling only when it's the player's turn?

Answer 1

Although not j2me specifically you should capture user input, the general strategy is to queue the input it until its time to process the input.

input ---> queue <---> Manager(loop)

This way you can even script input for debug purposes.

So you don't need a new thread. Each time the user presses key you store them in a buffer, and then process the contents of the buffer when necessary. If the player buffer has no input, the manager should skip all gameplay, do animations and then start over (since the game is not an action game).

Answer 2

I would avoid threading for the game logic as J2ME threading, depending on manufacturer of course, does not do a great job of sharing the limited resources. You will often see pauses while a thread does heavy processing. I would only recommend threads for loading or network connectivity features as in this case you will just be giving the user basic "Loading..." feedback.

To handle this, I would not have sub-loops to update each of the AI in one frame. I would do something like following in the run function:

public void run() {
    while(true) {
        // Update the Game
        if(gameManager.isUsersTurn()) {
            // Collect User Input
            // Process User Input
            // Update User's State
        }
        else {
            // Update the active NPC based on their current state
            gameManager.updateCurrentNPC();
        }

        // Do your drawing
    }
}

You want to avoid having everything updated in one frame as 1) the updating might be slow, resulting in no immediate visual feedback for the user 2) you can't animate each individual NPC as they make their action. With this setup you could have NPC states, NPC_DECIDE_MOVE and NPC_ANIMATING, that would allow you further control of what the NPC is doing. NPC_ANIMATING would basically put the game in a waiting state for the animation to take place, avoiding any further processing until the animation is complete. Then it could move on to the next NPC's turn.

Also, I would just have a gameManager.update() and gameManager.paint(g) (paint would be called from paint) that would handle everything and keep the run method thin.

Finally, did you look into flushGraphics()? With the GameCanvas you usually create a Graphics object, draw everything to that and then call flushGraphics(), then wait. The method you mention is the way of tackling it for the Canvas class. Just thought I would mention this and post a link: Game Canvas Basics