Qt 5.8 | Qt Multimedia | Spectrum Example | spectrograph.cpp Example File

Qt 5.8.0 Reference Documentation

# spectrograph.cpp Example File

multimedia/spectrum/app/spectrograph.cpp

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      #include "spectrograph.h"
      #include <QDebug>
      #include <QMouseEvent>
      #include <QPainter>
      #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();
      }