0.15 Xna0128-improving the sprite class

Revised: Mon May 09 17:04:23 CDT 2016

This page is part of a Book titled XNA Game Studio .

Table of Contents

• Table of Contents
• Preface
  • Viewing tip
    • Figures
    • Listings
• General background information
• Preview
  • The screen output
  • Lots and lots of sprites
• Discussion and sample code
  • The Sprite class
    • Properties
    • Other instance variables
    • The first three property accessor methods
    • The property accessor method for Speed
      • The set side
      • The get side
    • The constructor
      • Load an image
      • A random number generator
    • The SetImage method
    • The Move method
      • To move or not to move
      • Keeping up on the average
      • Code in the body of the if statement
        • Add the direction vector to the position vector
        • A collision with an edge of the game window
        • Modify the position and call the NewDirection method
      • The end of the Move method
    • The method named NewDirection
      • The length of the direction vector and the signs of the components
        • Compute the hypotenuse
        • Use the conditional operator
      • Compute components of a new direction vector
        • Compute a new random value for the X component
        • Compute a consistent value for the Y component
        • Adjust the signs of the X and Y components
        • A new direction vector with the same length in the same quadrant
    • The Draw method
    • The end of the Sprite class
  • The Game1 class
    • Instance variables
    • The modified constructor
    • The overridden LoadContent method
      • Instantiate all of the space rock sprites
        • Call the Sprite constructor
        • Set the property values
      • Instantiate and set properties on the power pills and the UFOs
    • The private DirectionVector method
      • Return a direction vector
      • The signs of the components
    • The overridden Update method
      • Very simple code
      • To move or not to move, that is the question
      • A characteristic of an object-oriented program
    • The overridden Game.Draw method
      • Erase and redraw the entire game window
  • Not the same approach as some other game engines
  • The end of the program
• Run the program
• Run my program
• Summary
• What's next?
• Miscellaneous
• Complete program listing

Preface

This module is one in a collection of modules designed primarily for teaching GAME 1343 Game and Simulation Programming I at Austin Community College in Austin, TX. These modules are intended tosupplement and not to replace the textbook.

An earlier module titled Getting Started provided information on how to get started programming with Microsoft's XNA Game Studio.

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 shot of the running program.

Listings

• Listing 1 . Beginning of the Sprite class.
• Listing 2 . The first three property accessor methods.
• Listing 3 . The property accessor method for Speed.
• Listing 4 . The constructor for the Sprite class.
• Listing 5 . The SetImage method.
• Listing 6 . Beginning of the Move method.
• Listing 7 . Add the direction vector to the position vector.
• Listing 8 . Process a collision with an edge of the game window.
• Listing 9 . Beginning of the method named NewDirection.
• Listing 10 . Compute components of a new direction vector.
• Listing 11 . The Sprite.Draw method.
• Listing 12 . Beginning of the Game1 class.
• Listing 13 . The modified constructor.
• Listing 14 . Beginning of the overridden LoadContent method.
• Listing 15 . Instantiate and set properties on the power pills and the UFOs.
• Listing 16 . The private DirectionVector method.
• Listing 17 . Tell the sprites to move.
• Listing 18 . The overridden Game.Draw method.
• Listing 19 . The class named Sprite for the project named XNA0128Proj.
• Listing 20 . The class named Game1 for the project named XNA0128Proj.