Using the Media Classes - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 408

GridPane.setHalignment(spectrumBars[i], HPos.CENTER);
gp.add(spectrumBars[i], i, 0);
}
}
The createSpectrumBars method creates a new array of SpectrumBar controls, one for each equalizer band
that was previously created. SpectrumBar is a custom control class that extends VBox to arrange a series of Rectangle
nodes in a vertical stack. The constructor parameters determine the maximum value of the bar, 100 in this case,
and the number of Rectangle nodes in the stack, which we have set to 20. The control has a setValue method
that determines how many of the bars are lit. For example, if we set a value of 50 (out of a maximum of 100), half of
the bars, 10 in this case, will be lit. The maximum width of each SpectrumBar is set to 44 to match the width of the
equalizer sliders. Each bar is then added to the GridPane layout in row zero where they are each centered horizontally
within their GridPane cell. Several examples of the control are shown in Figure 9-7 . We do not list the code for
SpectrumBar because creating a custom control is not the focus of this chapter. If you would like to view the source
code for this control, it is in SpectrumBar.java in the AudioPlayer4 example project.
Figure 9-7. A row of six SpectrumBar controls
Listing 9-24 also shows a new line in the createEQInterface method that instantiates a new instance of the
SpectrumListener class. This class is an implementation of the AudioSpectrumListener interface. Its job is to listen
for spectrum data updates, calculate the magnitude of the frequencies that lie within each of the equalizer bands we
have defined, and update the corresponding SpectrumBar with this calculated value. Listing 9-25 shows the class and
its initialization code.
Listing 9-25. The SpectrumListener Class
class SpectrumListener implements AudioSpectrumListener {
private final SpectrumBar[] bars;
private double minValue;
private double[] norms;
private int[] spectrumBucketCounts;
SpectrumListener(double startFreq, MediaPlayer mp, SpectrumBar[] bars) {
this.bars = bars;
this.minValue = mp.getAudioSpectrumThreshold();
this.norms = createNormArray();
int bandCount = mp.getAudioSpectrumNumBands();
this.spectrumBucketCounts = createBucketCounts(startFreq, bandCount);
}