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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.

Figures

  • Figure 1 . Screen output from program named Slick0130a.

Listings

  • Listing 1 . The start method of the AppGameContainer class.
  • Listing 2 . The gameLoop method of the AppGameContainer class.
  • Listing 3 . Beginning of the updateAndRender method of the GameContainer class.
  • Listing 4 . The remainder of the updateAndRender method of the GameContainer class.
  • Listing 5 . Beginning of the class named Slick0130a.
  • Listing 6 . The main method.
  • Listing 7 . The overridden init method.
  • Listing 8 . The overridden update method.
  • Listing 9 . The overridden render method.
  • 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:

  • setup
  • getDelta
  • gameLoop

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.

Questions & Answers

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LITNING
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Sahil
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Bob
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brayan
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research.net
kanaga
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Introduction about quantum dots in nanotechnology
Praveena Reply
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Anassong Reply
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s. Reply
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NANO
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Lily
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Damian
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Source:  OpenStax, Anatomy of a game engine. OpenStax CNX. Feb 07, 2013 Download for free at https://legacy.cnx.org/content/col11489/1.13
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