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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

Transforming Images

We have already seen back in Chapter 15 that we can apply a transformation to a graphics context to modify the user coordinate system relative to the device coordinate system. The transformation can be a translation, a rotation, a scaling operation, a shearing operation or a combination of all four. Of course, such a transformation applies to images that you draw as well as anything else.

In our previous example we adjusted the size of the applet to accommodate the image. In many situations you would not want to do this. Typically there are likely to be all kinds of things on the web page so you would want your applet to keep within the space allotted to it. We could have done this by scaling the image to fit the space available. Rather than go over the old ground let's create a new applet to try this out, and to add a bit of spice this time we will spin the image about its center, rather than dropping it. That way we will get to use a more complicated transform.

Try It Out – Spinning an Image

This applet will create an animation that spins the image about its center point. We will therefore need to make the diagonal of the image fit within both the height and width of the applet if we want to see all of it as it rotates. We also want the scaled image to fit in the center of the applet, so we will translate the user space after we have applied the scale transform.

Once the image is loaded, we can calculate the length of the diagonal of the image as the square root of the sum of the squares of the width and height. We can then calculate the scale factor that we require by dividing the width and height of the applet by the diagonal of the image, and taking the minimum of these two values. We can create an AffineTransform object in the init() method that combines both the scaling and the translation, and then just apply it in the paint() method for the ImagePanel class.

This applet class will contain the same methods as the previous example but with different implementations. The rotation will be accomplished by an additional transformation. We will also have an inner ImagePanel class to define the panel that will display the image. This will only differ in the implementation of the paint() method.

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