Swing Hacks

Add a Third Dimension to Swing #63

Chapter 8, Rendering

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319

HACK

As you can see, you end up with a black background in the Canva3D. Because

the only way to get rid of a component’s background is to call

setOpaque(false)

—which is defined by

JComponent

and thus isn’t available

to AWT components—you are stuck with this ugly background. Indeed, as

a lightweight component, the canvas cannot be made transparent. Things

get even worse when you try to add a menu bar to the application because of

the order in which components are painted: lightweight first, heavyweight

next. Figure 8-10 shows an example of what happens when a pop-up menu

is drawn by Swing. Because it is a lightweight component, it is drawn before

Canvas3D

, when it should be drawn after the canvas.

Thankfully, this new problem (it’s all AWT’s fault!) was so annoying that

the Swing team decided to add a workaround for it. You can simply force all

pop-up menus of your applications to be created as heavyweight compo-

nents instead of lightweight components. A single line of code is enough to

fix the problem:

JPopupMenu.setDefaultLightWeightPopupEnabled(false);

If you invoke this method before you create the first JMenu or JPopupMenu,

you ensure your menus will be drawn on top of heavyweight components.

So, this takes care of one issue, but you still need to deal with the black

background problem.

Faking Transparency

Because you cannot change the opacity of the Canvas3D, you are left with

only two possible solutions. The first is to get rid of Swing, go back to AWT,

and offer a crappy interface to the users. Because this doesn’t seem like too

great an option, we’ll just have to fake transparency.

Figure 8-10. Lightweight components are drawn behind heavyweight components

320

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Chapter 8, Rendering

#63 Add a Third Dimension to Swing

HACK

A Java3D scene is represented as a graph in which every node is an object or

a group of objects. A close look at the package

com.sun.j3d.utils.geometry

reveals the existence of the

Background

class, which you can use to change

the background of the 3D scene. For instance, you can create an Alpine

scene just by adding a background with a photo of the Alps as its texture.

Therefore, to fake transparency, you just have to use the window’s content

panel as texture for a new

Background object that you then add to the scene

graph. This is how AmazonPick creates the Java3D scene and adds a special

background:

public void createScene( )

{

BranchGroup objRoot = new BranchGroup( );

objRoot.addChild(createBackground( ));

// creates the whole scene

}

In Java3D, the scene is an instance of BranchGroup. By adding the Background

created by the method createBackground( ) as a child of the scene node, you

can set the background of the scene. The background itself is created like

this:

protected Background createBackground( )

{

BufferedImage image;

image = new BufferedImage(c3d.getParent().getWidth( ),

c3d.getParent().getHeight( ),

BufferedImage.TYPE_INT_RGB);

getContentPane().paint(image.getGraphics( ));

BufferedImage subImage;

subImage = new BufferedImage(CANVAS3D_WIDTH,

CANVAS3D_HEIGHT,

BufferedImage.TYPE_INT_RGB);

Graphics2D subGraphics = (Graphics2D) subImage.getGraphics( );

subGraphics.drawImage(image, null, -c3d.getX(), -c3d.getY( ));

ImageComponent2D backImage;

backImage = new ImageComponent2D(ImageComponent2D.FORMAT_RGB,

subImage)

Background bg = new Background(backImage);

BoundingSphere bounds = new BoundingSphere( );

bounds.setRadius(100.0);

bg.setApplicationBounds(bounds);

return bg;

}

The texture is created in two steps. The first is to create a BufferedImage

called image on which you paint the content panel of the window. Notice

that the picture has the same dimensions as the content panel. Calling the