Swing Hacks

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Chapter 1, Basic JComponents

#3 Fill Your Borders with Pretty Pictures

HACK

H A C K

#3

Fill Your Borders with Pretty Pictures

Hack #3

Swing comes with a set of customizable borders, but sometimes you want

more than they provide. This hack shows how to create a completely image-

based border that can be resized.

Swing has a prefabricated border, called the MatteBorder, which can accept

an image in its constructor. For simple tiled backgrounds, such as a checker-

board pattern, this works fine. However, if you want to have particular

images in each corner, creating a fully resizable image border, then you’ll

need something more powerful. Fortunately, Swing makes it very easy to

create custom border classes. The image border in this hack will produce a

border that looks like Figure 1-12.

The first step to any custom border is to subclass

AbstractBorder and imple-

ment the

paintBorder( ) method. The class will take eight images in the con-

structor, one for each corner and each side; all the code is shown in

Example 1-6.

Figure 1-12. An image-based border

Example 1-6. Building an image-based border

public class ImageBorder extends AbstractBorder {

Image top_center, top_left, top_right;

Image left_center, right_center;

Image bottom_center, bottom_left, bottom_right;

Insets insets;

public ImageBorder(Image top_left, Image top_center, Image top_right,

Image left_center, Image right_center,

Image bottom_left, Image bottom_center, Image bottom_right) {

this.top_left = top_left;

this.top_center = top_center;

this.top_right = top_right;

this.left_center = left_center;

this.right_center = right_center;

this.bottom_left = bottom_left;

this.bottom_center = bottom_center;

this.bottom_right = bottom_right;

}

Fill Your Borders with Pretty Pictures #3

Chapter 1, Basic JComponents

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15

HACK

The two methods after the constructor control the border insets. These are

the gaps between the panel’s outer edge (and its parent) and the inner edge

of the panel where the panel’s children are drawn.

setInsets( ) lets you set

any size insets, but most of the time you want the insets to be based on the

actual images that make up the border. The implementation of

getBorderInsets( ) returns the insets variable if it’s not null. However, if the

developer didn’t set the insets, then they will be derived from the widths and

heights of the images that make up each side of the border (top, bottom,

left, and right).

To actually draw the border, align the corner images to the appropriate cor-

ners and then tile the side images along each border side. Doing this will

require using the

TexturePaint class, which is an implementation of the

Paint interface. Unfortunately, TexturePaint takes only BufferedImages, not

regular ones, so you’ve got to convert your images before use.

BufferedImages are a special form of image that the Java2D framework can

read and write at a pixel level. The standard

Image is controlled by the oper-

ating system and is very difficult to access at the pixel level. Java doesn’t let

you do a straight conversion between the two kinds of images, but you can

just draw one image on top of another, which is what this method in the

ImageBorder class does:

public BufferedImage createBufferedImage(Image img) {

BufferedImage buff = new BufferedImage(img.getWidth(null),

img.getHeight(null), BufferedImage.TYPE_INT_ARGB);

Graphics gfx = buff.createGraphics( );

gfx.drawImage(img, 0, 0, null);

gfx.dispose( );

return buff;

}

public void setInsets(Insets insets) {

this.insets = insets;

}

public Insets getBorderInsets(Component c) {

if(insets != null) {

return insets;

} else {

return new Insets(top_center.getHeight(null),

left_center.getWidth(null),

bottom_center.getHeight(null), right_center.getWidth(null));

}

}

Example 1-6. Building an image-based border (continued)