com.jme.app
Class FixedLogicrateGame

java.lang.Object
  extended by com.jme.app.AbstractGame
      extended by com.jme.app.FixedLogicrateGame

public abstract class FixedLogicrateGame
extends AbstractGame

A game that attempts to run at a fixed logic rate.

The main loop makes every effort to update at the specified rate. The goal is to keep a consistent game-play speed regardless of the frame rate achieved by the visuals (i.e. the game will render as fast as the hardware permits, while running it's logic at a fixed rate). This gives tighter control on how the game state is processed, including such things as AI and physics.

The concept behind this is forcing every game logic tick to represent a fixed amount of real-time. For example, if the logic is updated at a rate of 15 times per second, and we have a person moving at 30 pixels per second, each update the person should move 2 pixels. To compensate for the non-constant frame rate, we smooth the visuals using interpolation. So, if the scene is rendered twice without the game logic being updated, we do not render the same thing twice.

Using a fixed time-step model has a number of benefits: game logic is simplified as there is no longer any need to add time deltas to achieve frame rate independence. There is also a gain in efficiency as the logic can be run at a lower frequency than the rendering, meaning that the logic may be updated only once every second game - a net save in time. Finally, because the exact same sequence of game logic code is executed every time, the game becomes deterministic (that is to say, it will run the exact same way every time).

Further extension of this class could be used to integrate both a fixed logic rate and a fixed frame rate.

Version:
$Revision: 4131 $, $Date: 2009-03-19 20:15:28 +0000 (Thu, 19 Mar 2009) $
Author:
Eric Woroshow

Nested Class Summary
 
Nested classes/interfaces inherited from class com.jme.app.AbstractGame
AbstractGame.ConfigShowMode
 
Field Summary
 
Fields inherited from class com.jme.app.AbstractGame
display, finished, settings
 
Constructor Summary
FixedLogicrateGame()
           
 
Method Summary
protected abstract  void cleanup()
          Called once the game loop has finished.
protected abstract  void initGame()
          Create and initialise all game data.
protected abstract  void initSystem()
          Initialise the display system.
protected  void quit()
          Quits the program abruptly using System.exit.
protected abstract  void reinit()
          Rebuild the system.
protected abstract  void render(float percentWithinTick)
          Renders the scene.
 void setLogicTicksPerSecond(int tps)
          setLogicTicksPerSecond sets the number of logic times per second the game should update the logic.
 void start()
          Ticks logic at a fixed rate while rendering as fast as hardware permits.
protected abstract  void update(float interpolation)
          Update the game state.
 
Methods inherited from class com.jme.app.AbstractGame
assertDisplayCreated, finish, getAttributes, getNewSettings, getVersion, setConfigShowMode, setConfigShowMode
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

FixedLogicrateGame

public FixedLogicrateGame()
Method Detail

setLogicTicksPerSecond

public void setLogicTicksPerSecond(int tps)
setLogicTicksPerSecond sets the number of logic times per second the game should update the logic. This should not be called prior to the application being start() -ed.

Parameters:
tps - the desired logic rate in ticks per second

start

public final void start()
Ticks logic at a fixed rate while rendering as fast as hardware permits.

Specified by:
start in class AbstractGame

quit

protected void quit()
Quits the program abruptly using System.exit.

Specified by:
quit in class AbstractGame
See Also:
AbstractGame.quit()

update

protected abstract void update(float interpolation)
Description copied from class: AbstractGame
Update the game state.

Any user input checks, changes to game physics, AI, networking, score table updates, and so on, should happen in this method. The rate at which this method is called will depend on the specific game implementation in use.

Note that this method should not update the screen.

Specified by:
update in class AbstractGame
Parameters:
interpolation - unused in this implementation
See Also:
AbstractGame.update(float interpolation)

render

protected abstract void render(float percentWithinTick)
Renders the scene. Under no circumstances should the render method alter anything that could directly or indirectly modify the game logic.

Specified by:
render in class AbstractGame
Parameters:
percentWithinTick - decimal value representing the position between update ticks
See Also:
AbstractGame.render(float interpolation)

initSystem

protected abstract void initSystem()
Description copied from class: AbstractGame
Initialise the display system.

This includes not just the DisplaySystem but also any other input and display related elements such as windows, cameras, and the input system.

Note that the display must be initialised in this method.

Specified by:
initSystem in class AbstractGame
See Also:
AbstractGame.initSystem()

initGame

protected abstract void initGame()
Description copied from class: AbstractGame
Create and initialise all game data.

What happens here is purely application dependent; it is where, for example, the initial scene graph and the starting environment could be loaded. It is suggested that any frequently used resources are loaded and cached in this method.

This method is called once after AbstractGame.initSystem() has completed.

Specified by:
initGame in class AbstractGame
See Also:
AbstractGame.initGame()

reinit

protected abstract void reinit()
Description copied from class: AbstractGame
Rebuild the system.

This method is called when the system requires rebuilding, for example is the screen resolution is altered. This method may be called at any time by client code.

Specified by:
reinit in class AbstractGame
See Also:
AbstractGame.reinit()

cleanup

protected abstract void cleanup()
Description copied from class: AbstractGame
Called once the game loop has finished.

Subclasses should use this method to release any resources, for example data that was loaded in the initXXX() methods.

Specified by:
cleanup in class AbstractGame
See Also:
AbstractGame.cleanup()