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Beginning Java 2- JDK 1.3 Version : Images and Animation

Buy this book Title: Beginning Java 2- JDK 1.3 Version ISBN: 1861003668 US Price: $ 49.99 Canadian Price: C$ 74.95 UK Price: £ 35.99 Publication Date: March 2000 Pages: 1230 © Wrox Press Limited, US and UK.

Beginning Java 2- JDK 1.3 Version
Images and Animation

Animation

You can create animated effects in Java on any component. You can create animation in a window or a panel, your buttons can have animated labels, and you can even animate your menu items if you wish. The general principles for producing animated images on your screen are the same as for a film. You display, or draw, a series of static images on the screen with a fixed interval of time between one image and the next. Each image differs slightly from its predecessor so that an object that is in a different position on successive images will appear to move. Since you know how to display one image you are part way there, and since you also know how to create a loop it is clearly not going to be too difficult to implement animated images.

There are two basic ways in which animation can be generated. You can create or obtain a set of images that are snapshots of the position of everything at fixed intervals, and then display them in sequence. Alternatively you can create or obtain an image of whatever you want to have moving, and display it at different positions at fixed intervals of time. Of course, before you display the moving entity at any given position, you must erase it at whatever position it was previously. Come to think of it, you already know one way to do this. Drawing a line or a circle in Sketcher produces an animated effect while you drag the mouse cursor.

Animation is often used in applets to make web pages more interesting and eye catching and there can be multiple, independent animated images in a page. The code producing an animated effect generally runs continuously, so you usually have to make this independent of any other code that may be running to allow the apparent concurrent operations. For this reason, you always implement code that generates an animated effect as a separate thread. If you don't implement your animation in a separate thread, it is unlikely to work properly, and other code that you expect to be executable while the animation is running will not work either. This goes for animations in applications as well as applets. We have already discussed threads in some detail so we just need to dredge the stuff up again and apply it for drawing images.

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