0.12 Using chroma key compositing to create transparent backgrounds

Table of contents

• Preface
  • General
    • Viewing tip
      • Figures
      • Listings
  • Supplemental material
• General background information
• Preview
• Discussion and sample code
• Run the program
• Resources
• Complete program listings
• Miscellaneous

Preface

General

This tutorial lesson is part of a series of lessons dedicated to object-oriented programming (OOP) with ActionScript.

Several ways to create and launch ActionScript programs

There are several ways to create and launch programs written in the ActionScript programming language. Many of the lessons in this series will useAdobe Flex as the launch pad for the sample ActionScript programs.

Getting started

An earlier lesson titled The Default Application Container provided information on how to get started programming with Adobe's Flex Builder 3.

The lesson titled Using Flex 3 in a Flex 4 World was added later to accommodate the release of Flash Builder 4. (See Baldwin's Flex programming website .)

You should study those lessons before embarking on the lessons in this series.

Some understanding of Flex MXML will be required

I also recommend that you study all of the lessons on Baldwin's Flex programming website in parallel with your study of these ActionScript lessons. Eventually you will probably need to understand both ActionScript and Flex andthe relationships that exist between them in order to become a successful ActionScript programmer.

Will emphasize ActionScript code

It is often possible to use either ActionScript code or Flex MXML code toachieve the same result. Insofar as this series of lessons is concerned, the emphasis will be on ActionScript code even in those cases where Flex MXML codemay be a suitable alternative.

Viewing tip

I recommend that you open another copy of this document 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 for the program named ChromaKey01.

Listings

• Listing 1 . Beginning of the class named Driver.
• Listing 2 . The constructor for the class named Driver.
• Listing 3 . The CREATION_COMPLETE event handler.
• Listing 4 . Beginning of the processChromaKey method.
• Listing 5 . Set selected alpha values to zero.
• Listing 6 . Store the modified pixel data in the bitmap.
• Listing 7 . Listing of the class named Driver.
• Listing 8 . Listing of the MXML file.

Supplemental material

I recommend that you also study the other lessons in my extensive collection of online programming tutorials. You will find a consolidated index at www.DickBaldwin.com .

General background information

In an earlier lesson titled Bitmap Basics , I explained the differences between Flex projects and ActionScript projects. I also introduced you to the classes named Bitmap and BitmapData .