Section 8.0. Introduction


8.0. Introduction

Flash 8 introduced the BitmapData class, one of the most important additions to the program at that time. Since its inception, Flash has been a vector-based tool. Vector graphics consist of mathematical descriptions of each graphical element. For example, a line starts at point x0, y0 and extends to point x1, y1. A bitmap, on the other hand, describes a graphic as a rectangular grid of values, with one color value assigned to each pixel.

The two main advantages of vector graphics are scaling and file size. When you scale a vector graphic, you are actually moving the points that make up the lines and curves of the graphic further apart or closer together. Thus, you can scale up or down to almost any size and still maintain smooth lines and curves. A bitmap, on the other hand, starts to look "blocky" as soon as you increase its size even slightly, since each pixel is simply made into a larger rectangle.

Since a vector graphic is nothing more than a list of coordinates that make up various lines, curves, and shapes, the file size tends to be quite low when compared to a bitmap graphic. Bitmap graphics, on the other hand, contain value information for each pixel in the image. For a 100x100-pixel image, this is a list of 10,000 individual values. Of course, most bitmap images use some form of compression to reduce the file size. Even so, they can be quite large.

The advantage of vector graphics went a long way to make Flash such a popular media format on the web. However, bitmaps are not without their own advantages. For one, bitmaps are much better at displaying photographic images. The amount of vectors it would take to describe all the shapes and color variations in a photograph would generally result in a larger file size than a bitmap of the same image.

Another benefit of bitmaps is that they are often easier on the processor than vectors are. In a vector image, each point's position must be calculated, and then the formulas for the lines and curves are calculated and drawn. Complex images can take quite a while to render. Bitmaps are relatively easy to render, though, no matter how complex they are. In terms of animation, you usually find very significant gains in speed and efficiency using bitmaps over vectors.

Before Flash 8, support for bitmap images was minimal. Although they could be loaded and displayed, there wasn't much you could do with them at runtime. The BitmapData class offers a nice set of tools for creating and manipulating bitmap graphics at runtime in Flash.




ActionScript 3. 0 Cookbook
ActionScript 3.0 Cookbook: Solutions for Flash Platform and Flex Application Developers
ISBN: 0596526954
EAN: 2147483647
Year: 2007
Pages: 351

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