0.10 Slick0200: developing a sprite class

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• Preview
• General background information
• Discussion and sample code
  • The class named Sprite01
  • The class named Slick0200
    • The init method
    • The update method
    • The render method
• Run the program
• Summary
• What's next?
• Miscellaneous
• Complete program listings

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.

The purpose of this module is to teach you how to develop a sprite class (see Sprite01 ) from which you can instantiate and animate swarms of sprite objects.

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 imagesand listings while you are reading about them.

Figures

• Figure 1 . Graphic output from program named Slick0200.
• Figure 2 . Graphic output from the earlier program.

Listings

• Listing 1 . Beginning of the class named Sprite01.
• Listing 2 . Beginning of the class named Slick0200.
• Listing 3 . Beginning of the init method.
• Listing 4 . Populate the array.
• Listing 5 . The update method.
• Listing 6 . The move method of the Sprite01 class.
• Listing 7 . The edgeBounce method of the Sprite01 class.
• Listing 8 . The render method.
• Listing 9 . The draw method of the Sprite01 class.
• Listing 10 . Source code for the program named Slick0200.
• Listing 11 . Source code for the sprite class named Sprite01.

Preview

I will present and explain a program that uses a class named Sprite01 (see Listing 11 ) to produce an animation of 1000 ladybug sprite objects flying around inside thegame window as shown in Figure 1 .

Figure 1 . Graphic output from program named Slick0200.

The frame rate

As you can see from the text in the upper-left corner of Figure 1 , the program is running at 62 frames per second. My rather old desktop computer can maintain this frame rate up to about 7000 sprite objects.Beyond that, it can no longer handle the computing load and the frame rate begins to decrease.

What you have learned

In the previous module, you learned how to use objects of the SpriteSheet class and the Animation class to perform relatively complex sprite sheet animations.

What you will learn

In this module, you will learn how to develop a sprite class from which you can instantiate and animate swarms of sprite objects. In the next two modules,you will learn how to put that class to work.

General background information

While the Slick2D library provides many useful classes, there is nothing to stop you from developing your own classes to work in combination with theSlick2D library classes. That is the thrust of this module.

In an earlier module titled Slick0150: A first look at sprite motion, collision detection, and timing control , you learned how to cause a single sprite to bounce around inside the game window as shown in Figure 2 .