Swing Hacks

324

|

Chapter 8, Rendering

#64 Turn the Spotlight on Swing

HACK

You can even go one step further: the more light you shed, the less darkness

there is. For instance, when several books are found, it is likely that the

search query was not very precise. This means the user will be more inter-

ested in lots of items. When the query yields only a few results, it is likely

that the user wants to see only a few specific items.

As you create several spotlights—one per result—the interface is less dark-

ened than with only one spotlight. If you take a close look at Figure 8-13,

you’ll be able to perceive the other books. Nevertheless, a single search

result will prevent the user from seeing the other books, as shown in

Figure 8-14.

Add the Spotlight

The implementation of spotlights for Swing is divided into two classes,

SpotlightPanel and Spotlight. The first class is a glass pane that needs to be

set up on a frame, and the second defines the location and the shape of a

spotlight. Here is an example of how to use spotlights:

SpotlightPanel glassPane = new SpotlightPanel( );

setGlassPane(glassPane);

Spotlight s1 = glassPane.addSpotlight(0, 0, 25, 50);

Spotlight s2 = glassPane.addSpotlight(100, 100, 30);

Figure 8-14. With only one spotlight, it is almost impossible to see the other books

Turn the Spotlight on Swing #64

Chapter 8, Rendering

|

325

HACK

Here, you create two spotlights: s1 and s2. The first is an ellipse 25-pixels

wide, 50-pixels high, and located at the top-left corner of the frame; the sec-

ond is a circle with a radius of 30 pixels and located 100 pixels away from

the top and the left of the frame’s border. Each spotlight is implemented as

an ellipse with the class

Ellipse2D.Double

, as shown in Example 8-11.

As you can see in the code, the

Spotlight class is fairly simple and contains

only two public methods. The first one,

getSpot( ), returns the Ellipse2D

instance used to draw the spotlight. It can also be used to dynamically

change the location and the size of the spotlight. Once you’ve installed a few

spotlights, you will be able to get

Ellipse2D to animate them. By moving

them around, shrinking them, or growing them, you can create stunning

effects. The second method of this class,

getArea( ), is used by

SpotlightPanel to define the amount of darkness according to the total area

occupied by the spotlights on the window. Thus, if you have enough spot-

lights to cover 80% of the window with light,

SpotlightPanel will use a

darkness of 20%. In short,

getArea( ) computes the geometrical area of the

spotlight’s ellipse.

The

SpotlightPanel panel class (shown in Example 8-12) only needs a few

methods as well. You must be able to create spotlights, to remove a particu-

lar spotlight, to remove all spotlights, and to paint spotlights on the screen.

You also need two constructors. If you look at the previous figures, you

should see that the spotlights’ borders are blurred to get a nicer rendering.

Example 8-11. Representing a spotlight with an Ellipse2D

public class Spotlight

{

protected Ellipse2D.Double spot;

protected Rectangle2D.Double bounds;

public Spotlight(int x, int y, int w, int h)

{

this.spot = new Ellipse2D.Double(x, y, w, h);

}

public Ellipse2D getSpot( )

{

return spot;

}

public double getArea( )

{

return Math.PI * spot.getWidth() * spot.getHeight( ) / 4.0;

}

}

326

|

Chapter 8, Rendering

#64 Turn the Spotlight on Swing

HACK

Unfortunately, the blurring method used in the painting algorithm is very

slow and prevents smooth animation of the spotlights. To account for this,

you need a special constructor to instruct the panel to draw blurred borders,

along with a constructor that leaves blurring at its default (on in this class,

although you may want to leave it off normally). When you need still spot-

lights, activate the blur to get a nicer result. On the contrary, when you want

to animate the spotlights, deactivate the blur to get full-speed animations.

The default constructor enables the blur. You can use the second construc-

tor and pass it

false to deactivate this option. The rendering of the blur

effect is done with the help of a

ConvolveOp. You learned about the inner

workings of a blur operation when you blurred disabled components

[Hack #9].

The constructor also creates an instance of

ArrayList in which all the spot-

lights are stored:

public Spotlight addSpotlight(int x, int y, int w, int h)

{

if (spotlights.size( ) == 0)

{

Example 8-12. Constructors of the SpotlightPanel class

public class SpotlightPanel extends JComponent implements MouseListener

{

protected boolean blur;

protected List spotlights;

protected ConvolveOp blurOp;

protected RenderingHints hints;

public SpotlightPanel( )

{

this(true);

}

public SpotlightPanel(boolean blur)

{

this.blur = blur;

spotlights = new ArrayList( );

blurOp = new ConvolveOp(getBlurKernel(3), ConvolveOp.EDGE_NO_OP, null);

hints = new RenderingHints(RenderingHints.KEY_RENDERING,

RenderingHints.VALUE_RENDER_QUALITY);

hints.put(RenderingHints.KEY_ANTIALIASING,

RenderingHints.VALUE_ANTIALIAS_ON);

hints.put(RenderingHints.KEY_FRACTIONALMETRICS,

RenderingHints.VALUE_FRACTIONALMETRICS_ON);

}

// other methods omitted

}