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1  Game Development / Performance Tuning / Fast engine.tick() design on: 2009-10-13 05:17:18
Hello all.

I am making a Java game.  It's intended target platform is NOT Windows, but I'm still going to write it in Java.  So, I have a pretty basic question, but there's a few different rather complicated answers.

My question is this: How can I make the most efficient engine, or main loop, which ticks and does gameplay action (moves character, enemies, etc.), while also dealing with repainting?  There are a few different ways to do so.

Method A:
Put delay in the tick() method.  Here, the game loop logic, and the repainting, is done on the same thread.  If the game processing and drawing takes longer than the delay, then the game will simply slow down.  I'll have to code efficiently!

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class GameThread extends Thread {
   public void run() {
      running = true;
      do {
         try {
            game.tick();
            display.repaint();
         } catch (Exception e) {
            e.printStackTrace();
         }
      } while (running);
   }
}
// ... Engine tick ...
   public void tick() {
      long start = System.nanoTime();

      // Do game logic
      doActions();

      // Wait until a given amount of time has passed
      while (now - lastFrameNs < DELAY_NS) {
         try {
            Thread.sleep(1);
         } catch (Exception e) {}
         now = System.nanoTime();
      }
   }


Method B:
Calculate the time delta in the tick() method, and move enemies and other game logic according to how much time has passed.  The game will always appear to run at the same speed, although the FPS will go higher or lower depending on the processing load of the game actions and drawing. 

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   long delta = System.currentTimeMillis() - lastLoopTime;
   lastLoopTime = System.currentTimeMillis();

   // Do game logic
   entity.moveBy(delta);


In the above logic, you see that enemies will move depending on the time taken.  So, if it took 50ms, they'll move by 10 pixels, or if it took 25ms, they'll move by 5 pixels.

The problem with this method, is that in-game logic timing becomes hard.  What if a gun is supposed to fire 3 times a second?  If the processing theoretically took a total of 1 second, I would have to fire the gun 3 times in the same tick(), which is bad because what if you'd want a back and forth between two entities (A interacts with B, B interacts with A, etc., instead of A interacts with B x 3, and THEN B interacts with A x 3).  Or, in some cases where the logic just fails, the gun would only fire once when it was supposed to fire three times.

Method C:

Hmmm, I can't think of a method C.   Smiley

Well, what are you guys' take on this?

Thanks!
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