Learning Java

Producing Image Data

There are two different approaches to generating image data. The easiest way is to treat the image as a drawing surface and use the methods of Graphics2D to render things into the image. The second way is to twiddle the bits of the image data yourself. This is harder, but it can be useful in specific cases: loading and saving images in files or mathematically analyzing image data are two examples.

Drawing Animations

Let’s begin with the simpler approach, rendering on an image. We’ll throw in a twist, to make things interesting: we’ll build an animation. Each frame will be rendered as we go along. This is very similar to the double buffering we examined in the last chapter, but this time we’ll use a timer, instead of mouse events, as the signal to generate new frames.

Swing performs double buffering automatically, so we don’t even have to worry about the animation flickering. Although it looks like we’re drawing directly to the screen, we’re really drawing into an image that Swing uses for double buffering. All we need to do is draw the right thing at the right time.

Let’s look at an example, Hypnosis, that illustrates the technique. This example shows a constantly shifting shape that bounces around the inside of a component. When screen savers first came of age, this kind of thing was pretty hot stuff. Hypnosis is shown in Figure 18.2; here is its source code:

//file: Hypnosis.java import java.awt.*; import java.awt.event.*; import java.awt.geom.GeneralPath; import ...