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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