Qt Reference Documentation

spectrograph.cpp Example File

demos/spectrum/app/spectrograph.cpp
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 #include "spectrograph.h"
 #include <QPainter>
 #include <QMouseEvent>
 #include <QDebug>
 #include <QTimerEvent>

 const int NullTimerId = -1;
 const int NullIndex = -1;
 const int BarSelectionInterval = 2000;

 Spectrograph::Spectrograph(QWidget *parent)
     :   QWidget(parent)
     ,   m_barSelected(NullIndex)
     ,   m_timerId(NullTimerId)
     ,   m_lowFreq(0.0)
     ,   m_highFreq(0.0)
 {
     setMinimumHeight(100);
 }

 Spectrograph::~Spectrograph()
 {

 }

 void Spectrograph::setParams(int numBars, qreal lowFreq, qreal highFreq)
 {
     Q_ASSERT(numBars > 0);
     Q_ASSERT(highFreq > lowFreq);
     m_bars.resize(numBars);
     m_lowFreq = lowFreq;
     m_highFreq = highFreq;
     updateBars();
 }

 void Spectrograph::timerEvent(QTimerEvent *event)
 {
     Q_ASSERT(event->timerId() == m_timerId);
     Q_UNUSED(event) // suppress warnings in release builds
     killTimer(m_timerId);
     m_timerId = NullTimerId;
     m_barSelected = NullIndex;
     update();
 }

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

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

     const int numBars = m_bars.count();

     // Highlight region of selected bar
     if (m_barSelected != NullIndex && numBars) {
         QRect regionRect = rect();
         regionRect.setLeft(m_barSelected * rect().width() / numBars);
         regionRect.setWidth(rect().width() / numBars);
         QColor regionColor(202, 202, 64);
         painter.setBrush(Qt::DiagCrossPattern);
         painter.fillRect(regionRect, regionColor);
         painter.setBrush(Qt::NoBrush);
     }

     QColor barColor(51, 204, 102);
     QColor clipColor(255, 255, 0);

     // Draw the outline
     const QColor gridColor = barColor.darker();
     QPen gridPen(gridColor);
     painter.setPen(gridPen);
     painter.drawLine(rect().topLeft(), rect().topRight());
     painter.drawLine(rect().topRight(), rect().bottomRight());
     painter.drawLine(rect().bottomRight(), rect().bottomLeft());
     painter.drawLine(rect().bottomLeft(), rect().topLeft());

     QVector<qreal> dashes;
     dashes << 2 << 2;
     gridPen.setDashPattern(dashes);
     painter.setPen(gridPen);

     // Draw vertical lines between bars
     if (numBars) {
         const int numHorizontalSections = numBars;
         QLine line(rect().topLeft(), rect().bottomLeft());
         for (int i=1; i<numHorizontalSections; ++i) {
             line.translate(rect().width()/numHorizontalSections, 0);
             painter.drawLine(line);
         }
     }

     // Draw horizontal lines
     const int numVerticalSections = 10;
     QLine line(rect().topLeft(), rect().topRight());
     for (int i=1; i<numVerticalSections; ++i) {
         line.translate(0, rect().height()/numVerticalSections);
         painter.drawLine(line);
     }

     barColor = barColor.lighter();
     barColor.setAlphaF(0.75);
     clipColor.setAlphaF(0.75);

     // Draw the bars
     if (numBars) {
         // Calculate width of bars and gaps
         const int widgetWidth = rect().width();
         const int barPlusGapWidth = widgetWidth / numBars;
         const int barWidth = 0.8 * barPlusGapWidth;
         const int gapWidth = barPlusGapWidth - barWidth;
         const int paddingWidth = widgetWidth - numBars * (barWidth + gapWidth);
         const int leftPaddingWidth = (paddingWidth + gapWidth) / 2;
         const int barHeight = rect().height() - 2 * gapWidth;

         for (int i=0; i<numBars; ++i) {
             const qreal value = m_bars[i].value;
             Q_ASSERT(value >= 0.0 && value <= 1.0);
             QRect bar = rect();
             bar.setLeft(rect().left() + leftPaddingWidth + (i * (gapWidth + barWidth)));
             bar.setWidth(barWidth);
             bar.setTop(rect().top() + gapWidth + (1.0 - value) * barHeight);
             bar.setBottom(rect().bottom() - gapWidth);

             QColor color = barColor;
             if (m_bars[i].clipped)
                 color = clipColor;

             painter.fillRect(bar, color);
         }
     }
 }

 void Spectrograph::mousePressEvent(QMouseEvent *event)
 {
     const QPoint pos = event->pos();
     const int index = m_bars.count() * (pos.x() - rect().left()) / rect().width();
     selectBar(index);
 }

 void Spectrograph::reset()
 {
     m_spectrum.reset();
     spectrumChanged(m_spectrum);
 }

 void Spectrograph::spectrumChanged(const FrequencySpectrum &spectrum)
 {
     m_spectrum = spectrum;
     updateBars();
 }

 int Spectrograph::barIndex(qreal frequency) const
 {
     Q_ASSERT(frequency >= m_lowFreq && frequency < m_highFreq);
     const qreal bandWidth = (m_highFreq - m_lowFreq) / m_bars.count();
     const int index = (frequency - m_lowFreq) / bandWidth;
     if(index <0 || index >= m_bars.count())
         Q_ASSERT(false);
     return index;
 }

 QPair<qreal, qreal> Spectrograph::barRange(int index) const
 {
     Q_ASSERT(index >= 0 && index < m_bars.count());
     const qreal bandWidth = (m_highFreq - m_lowFreq) / m_bars.count();
     return QPair<qreal, qreal>(index * bandWidth, (index+1) * bandWidth);
 }

 void Spectrograph::updateBars()
 {
     m_bars.fill(Bar());
     FrequencySpectrum::const_iterator i = m_spectrum.begin();
     const FrequencySpectrum::const_iterator end = m_spectrum.end();
     for ( ; i != end; ++i) {
         const FrequencySpectrum::Element e = *i;
         if (e.frequency >= m_lowFreq && e.frequency < m_highFreq) {
             Bar &bar = m_bars[barIndex(e.frequency)];
             bar.value = qMax(bar.value, e.amplitude);
             bar.clipped |= e.clipped;
         }
     }
     update();
 }

 void Spectrograph::selectBar(int index) {
     const QPair<qreal, qreal> frequencyRange = barRange(index);
     const QString message = QString("%1 - %2 Hz")
                                 .arg(frequencyRange.first)
                                 .arg(frequencyRange.second);
     emit infoMessage(message, BarSelectionInterval);

     if (NullTimerId != m_timerId)
         killTimer(m_timerId);
     m_timerId = startTimer(BarSelectionInterval);

     m_barSelected = index;
     update();
 }
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