Qt Reference Documentation

levelmeter.cpp Example File

demos/spectrum/app/levelmeter.cpp
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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);
 }
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