levelmeter.cpp Example File

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  #include "levelmeter.h"

  #include <math.h>

  #include <QPainter>
  #include <QTimer>
  #include <QDebug>

  // Constants
  const int RedrawInterval = 100; // ms
  const qreal PeakDecayRate = 0.001;
  const int PeakHoldLevelDuration = 2000; // ms

  LevelMeter::LevelMeter(QWidget *parent)
      :   QWidget(parent)
      ,   m_rmsLevel(0.0)
      ,   m_peakLevel(0.0)
      ,   m_decayedPeakLevel(0.0)
      ,   m_peakDecayRate(PeakDecayRate)
      ,   m_peakHoldLevel(0.0)
      ,   m_redrawTimer(new QTimer(this))
      ,   m_rmsColor(Qt::red)
      ,   m_peakColor(255, 200, 200, 255)
  {
      setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Preferred);
      setMinimumWidth(30);

      connect(m_redrawTimer, SIGNAL(timeout()), this, SLOT(redrawTimerExpired()));
      m_redrawTimer->start(RedrawInterval);
  }

  LevelMeter::~LevelMeter()
  {

  }

  void LevelMeter::reset()
  {
      m_rmsLevel = 0.0;
      m_peakLevel = 0.0;
      update();
  }

  void LevelMeter::levelChanged(qreal rmsLevel, qreal peakLevel, int numSamples)
  {
      // Smooth the RMS signal
      const qreal smooth = pow(qreal(0.9), static_cast<qreal>(numSamples) / 256); // TODO: remove this magic number
      m_rmsLevel = (m_rmsLevel * smooth) + (rmsLevel * (1.0 - smooth));

      if (peakLevel > m_decayedPeakLevel) {
          m_peakLevel = peakLevel;
          m_decayedPeakLevel = peakLevel;
          m_peakLevelChanged.start();
      }

      if (peakLevel > m_peakHoldLevel) {
          m_peakHoldLevel = peakLevel;
          m_peakHoldLevelChanged.start();
      }

      update();
  }

  void LevelMeter::redrawTimerExpired()
  {
      // Decay the peak signal
      const int elapsedMs = m_peakLevelChanged.elapsed();
      const qreal decayAmount = m_peakDecayRate * elapsedMs;
      if (decayAmount < m_peakLevel)
          m_decayedPeakLevel = m_peakLevel - decayAmount;
      else
          m_decayedPeakLevel = 0.0;

      // Check whether to clear the peak hold level
      if (m_peakHoldLevelChanged.elapsed() > PeakHoldLevelDuration)
          m_peakHoldLevel = 0.0;

      update();
  }

  void LevelMeter::paintEvent(QPaintEvent *event)
  {
      Q_UNUSED(event)

      QPainter painter(this);
      painter.fillRect(rect(), Qt::black);

      QRect bar = rect();

      bar.setTop(rect().top() + (1.0 - m_peakHoldLevel) * rect().height());
      bar.setBottom(bar.top() + 5);
      painter.fillRect(bar, m_rmsColor);
      bar.setBottom(rect().bottom());

      bar.setTop(rect().top() + (1.0 - m_decayedPeakLevel) * rect().height());
      painter.fillRect(bar, m_peakColor);

      bar.setTop(rect().top() + (1.0 - m_rmsLevel) * rect().height());
      painter.fillRect(bar, m_rmsColor);
  }