0.5 Slick0150: a first look at sprite motion, collision detection

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• Preview
• General background information
• Discussion and sample code
  • A program witha relatively constant frame rate - Slick0150a
    • The screen output for Slick0150a
    • Beginning of the class named Slick0150a
    • The constructor and the main method
    • The init method
    • The update method
    • The render method
  • A program with ahighly variable frame rate Slick0150b
    • The screen output for Slick0150b
    • The render method
    • The update method
• Run the programs
• 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 teach you how to make sprites move at a constant speed in front of an image in the face of a widely varying frame rate. You will also learn about a rudimentary form of collision detection.

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 . Image of a ladybug.
• Figure 2 . Background image.
• Figure 3 . Screen shot of the program named Slick0150a.
• Figure 4 . Screen shot of the program named Slick0150b.
• Figure 5 . Screen shot of the program named Slick0150b without correction for varying frame rate.

Listings

• Listing 1 . Beginning of the class named Slick0150a.
• Listing 2 . The init method for Slick0150a.
• Listing 3 . Beginning of the update method for Slick0150a.
• Listing 4 . Detection of collision with right edge.
• Listing 5 . Test for collisions on other three sides of game window.
• Listing 6 . The render method for Slick150a.
• Listing 7 . The render method for Slick150b.
• Listing 8 . Beginning of the update method for Slick0150b.
• Listing 9 . Source code for the program named Slick0150a.
• Listing 10 . Source code for the program named Slick0150b.

Preview

What you have learned

In the previous module, you learned that while there are many classes and interfaces in the Slick2D library with names that match the names of classes andinterfaces in the standard edition Java library, they are not the same.

You learned that you can access the Slick2D documentation at (External Link) . (A copy of the documentation is also included in the distribution zip file.)

You learned how to set the drawing mode so that bitmap images drawn in the game window will either honor or not honor transparent pixels.

You learned how to draw bitmap images in the game window using both the draw methods of the Image class and the drawImage methods of the Graphics class.

What you will learn