levelmeter.cpp Example File

 /****************************************************************************
 **
 ** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
 ** All rights reserved.
 ** Contact: Nokia Corporation (qt-info@nokia.com)
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** You may use this file under the terms of the BSD license as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
 **     the names of its contributors may be used to endorse or promote
 **     products derived from this software without specific prior written
 **     permission.
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #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);
 }