Swing Hacks

Indefinite Progress Indicator #47

Chapter 6, Transparent and Animated Windows

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249

HACK

Picture as Indicator

The first solution relies on cycling the brightness of a picture in a panel.

Instead of moving a rectangle back and forth, you can increase and decrease

the brightness of a picture. The result is much more appealing and lets you

choose an adequate picture regarding the current running task. Figure 6-14

shows the

AnimatedPanel

in action.

When you click the Start button, the contents of the Animated tab are

replaced by a panel containing a picture and a message. With the picture’s

brightness cycles, as shown in Figure 6-15, you can see the most bright state

on the left and the less bright state on the right.

Figure 6-14. The first tab demonstrates the use of a picture as an indefinite progress

indicator

Figure 6-15. AnimatedPanel displays a picture and cycles its brightness

250

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Chapter 6, Transparent and Animated Windows

#47 Indefinite Progress Indicator

HACK

To change the brightness of the picture dynamically, AnimatedPanel starts an

animation thread responsible for computing the brightness over the time:

public void start( ) {

this.animator = new Thread(new HighlightCycler( ), "Highlighter");

this.animator.start( );

}

class HighlightCycler implements Runnable {

private int way = 1;

private final int LOWER_BOUND = 10;

private final int UPPER_BOUND = 35;

private int value = LOWER_BOUND;

public void run( ) {

while (true) {

try {

Thread.sleep(1000 / (UPPER_BOUND - LOWER_BOUND));

} catch (InterruptedException e) {

return;

}

value += this.way;

if (value > UPPER_BOUND) {

value = UPPER_BOUND;

this.way = -1;

} else if (value < LOWER_BOUND) {

value = LOWER_BOUND;

this.way = 1;

}

synchronized (convolvedImage) {

setBrightness((float) value / 10);

setGradientFactor((float) value / UPPER_BOUND);

}

}

}

}

When the start( ) method of the panel is called, a new thread is spawned to

run

HighlightCycler. The animation loop is very simple, and it increases or

decreases the variable

value until its value reaches LOWER_BOUND or UPPER_

BOUND

. Then, setBrightness( ) is invoked to change the brightness of the pic-

ture. Given the values of the bounds, the brightness swings between 1.0

(unchanged) and 3.5 (the picture is 3.5 times brighter). You can notice this

call is synchronized with the object

convolvedImage, which is one of the two

BufferedImages contained in AnimatedPanel. This image is the result of a fil-

ter applied on

originalImage, the picture that contains the unchanged origi-

nal picture. As applying the filter can take some time, the code synchronizes

on

convolvedImage to ensure the previous filtering is done before running a

new one. This code shows how to change the brightness of the picture: