0.13 Xna0124-using background images and color key transparency

Revised: Sun May 08 15:53:42 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
  • Layer depth
  • Color key transparency
  • Transparent green
  • Store your image in a lossless image file
  • Be aware of the default values
• Preview
  • The UFO image
  • Image of the planet
  • The screen output
    • Flying a relatively straight path
    • The background is moving
    • Preparing to change course
    • Flying towards the camera
    • Heading for home
• Discussion and sample code
  • The class named Game1
  • The constructor for the class named Game1
    • Setting the size of the game window
    • Maintaining the aspect ratio
  • The overridden LoadContent method
    • The new material
    • Compute the position of the UFO relative to the game window
    • Compute the base scale factor for the background image
    • Not the only scale factor
    • An optical illusion
  • The overridden Update method
    • Controlling the animation speed
      • Draw new material every 83 milliseconds
      • Apply dynamic scaling to the background image
        • Two components in the scale factor
        • An optical illusion
        • The dynamic portion of the overall scale factor
    • Changing the origin of the background image
      • Increasing the scale alone is insufficient
      • Need to stabilize the location of the planet in the game window
      • Examples
    • The end of the Update method
  • The overridden Game.Draw method
    • No need to clear the game window
    • Two main sections of code
      • Draw the background image showing the planet
      • Draw the UFO
        • Center the UFO image on the position
        • The UFO does not move
        • The front of the z-order stack
  • The end of the program
  • Recap on the origin and position parameters
• Run the program
• Run my program
• Summary
• 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 . Property settings for green transparency.
• Figure 2 . The UFO image.
• Figure 3 . Reduced version of the alien planet image.
• Figure 4 . The UFO approaching the planet from some distance away.
• Figure 5 . Flying over the planet.
• Figure 6 . Flying over the planet.
• Figure 7 . Flying over the planet.
• Figure 8 . Preparing to change course.
• Figure 9 . Flying towards the camera very close to the surface of the planet.
• Figure 10 . Still flying towards the camera very close to the surface of the planet.
• Figure 11 . Almost touching the rings around the planet.
• Figure 12 . Heading for home.