Learn how a game program written with the Slick game library creates and maintains a game loop.
Table of contents
Preface
This module is one in a collection of modules designed to teach you about
the anatomy of a game engine.
Although the modules in this collection will concentrate on the Java game
library named Slick2D, theconcepts involved and the knowledge that you will gain is applicable to
different game engines written in different programming languages as well.
Viewing tip
I recommend that you open another copy of this module in a separate
browser window and use the following links to easily find and view the Figuresand Listings while you are reading about them.
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Figure 1 . Screen output from program named Slick0130a.
Listings
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Listing 1 . The start method of the AppGameContainer class.
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Listing 2 . The gameLoop method of the AppGameContainer class.
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Listing 3 . Beginning of the updateAndRender method of the GameContainer class.
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Listing 4 . The remainder of the updateAndRender method of the GameContainer class.
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Listing 5 . Beginning of the class named Slick0130a.
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Listing 6 . The main method.
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Listing 7 . The overridden init method.
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Listing 8 . The overridden update method.
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Listing 9 . The overridden render method.
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Listing 10 . Source code for the program named Slick0130a.
Preview
What you have learned
The main purpose of this and the previous module is to analyze the behavior
of the Slick2D game engine when you call the
start method to
cause a Slick2D game program to start running.
In the previous module, you learned how and why you should extend the
BasicGame class instead of implementing the
Game interface directly.
You learned about the behavior of the constructors for the
AppGameContainer class.
You learned that the
start method of the
AppGameContainer class
(see
Listing 1 ) calls the following three methods:
You learned about the behavior of the
setup and
getDelta methods.
What you will learn
I will explain the overall behavior of the
gameLoop method in this module.
In addition, you will learn
- about a property of the
GameContainer class
named
running , and how it is used by the
start method to keep the game loop running,
- about the salient features of the
gameLoop method of the
AppGameContainer class,
- about the
updateAndRender method of the
GameContainer class and how it decides when and if to call the
update and
render methods of the object of the
Game class that is wrapped in the container,
- about the difference between normal delta and smoothed delta,
- about
minimumLogicInterval and
maximumLogicInterval and how the contents of those two variables are
used to determine if, when, and how many times to call the
update method during each iteration of the game loop,
- how the contents of
minimumLogicInterval and
maximumLogicInterval are used to determine the value that
is passed as delta each time the
update method is called,
- that the
render method is normally called once and only
once during each iteration of the game loop,
- how you can use the value of delta that is received by the
update method to control the behavior of a game program,
- that you can set the size of the game window when you instantiate an
object of the
AppGameContainer class by passing dimension
parameters to the constructor,
- that you can set the target frame rate by calling the
setTargetFrameRate method on the
GameContainer object, and
- how to display text in the game window.
