このコードは、scrollPane 内の波形を表示します。
var scrollPane = new JScrollPane
var waveform = new Waveform(trackModel) // JPanel with waveform
scrollPane.setViewportView(waveform)
そして、これはscrollPaneの灰色の背景だけを示しています:
var scrollPane = new JScrollPane
var layeredPane = new JLayeredPane
var waveform = new Waveform(trackModel) // JPanel with waveform
layeredPane.add(waveform, JLayeredPane.DEFAULT_LAYER)
layeredPane.setPreferredSize(trackModel.getSize())
scrollPane.setViewportView(layeredPane)
波形（Waveform extends JPanel）が表示されない理由がわかりません。詳細は次のとおりです。
System.out.println("waveform visibility: " + waveform.isVisible)
System.out.println("layeredPane visibility: " + layeredPane.isVisible)
System.out.println("scrollPane visibility: " + scrollPane.isVisible)
System.out.println("waveform dimensions: " + waveform.getPreferredSize.width + "/" + waveform.getPreferredSize.height)
System.out.println("layeredPane dimensions: " + layeredPane.getPreferredSize.width + "/" + layeredPane.getPreferredSize.height)
System.out.println("scrollPane dimensions: " + scrollPane.getPreferredSize.width + "/" + scrollPane.getPreferredSize.height)
System.out.println("waveform dimensions: " + waveform.getWidth + "/" + waveform.getHeight)
System.out.println("layeredPane dimensions: " + layeredPane.getWidth + "/" + layeredPane.getHeight)
System.out.println("scrollPane dimensions: " + scrollPane.getWidth + "/" + scrollPane.getHeight)
そして出力：
waveform visibility: true
layeredPane visibility: true
scrollPane visibility: true
waveform dimensions: 40315/200
layeredPane dimensions: 40315/200
scrollPane dimensions: 40318/203
waveform dimensions: 0/0
layeredPane dimensions: 0/0
scrollPane dimensions: 0/0