Qt 5.8 | Qt Multimedia | Media Player Example | histogramwidget.cpp Example File

Qt 5.8.0 Reference Documentation

# histogramwidget.cpp Example File

multimediawidgets/player/histogramwidget.cpp

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      #include "histogramwidget.h"
      #include <QPainter>

      HistogramWidget::HistogramWidget(QWidget *parent)
          : QWidget(parent)
          , m_levels(128)
          , m_isBusy(false)
      {
          m_processor.moveToThread(&m_processorThread);
          qRegisterMetaType<QVector<qreal> >("QVector<qreal>");
          connect(&m_processor, SIGNAL(histogramReady(QVector<qreal>)), SLOT(setHistogram(QVector<qreal>)));
          m_processorThread.start(QThread::LowestPriority);
      }

      HistogramWidget::~HistogramWidget()
      {
          m_processorThread.quit();
          m_processorThread.wait(10000);
      }

      void HistogramWidget::processFrame(QVideoFrame frame)
      {
          if (m_isBusy)
              return; //drop frame

          m_isBusy = true;
          QMetaObject::invokeMethod(&m_processor, "processFrame",
                                    Qt::QueuedConnection, Q_ARG(QVideoFrame, frame), Q_ARG(int, m_levels));
      }

      void HistogramWidget::setHistogram(QVector<qreal> histogram)
      {
          m_isBusy = false;
          m_histogram = histogram;
          update();
      }

      void HistogramWidget::paintEvent(QPaintEvent *event)
      {
          Q_UNUSED(event);

          QPainter painter(this);

          if (m_histogram.isEmpty()) {
              painter.fillRect(0, 0, width(), height(), QColor::fromRgb(0, 0, 0));
              return;
          }

          qreal barWidth = width() / (qreal)m_histogram.size();

          for (int i = 0; i < m_histogram.size(); i++) {
              qreal h = m_histogram[i] * height();
              // draw level
              painter.fillRect(barWidth * i, height() - h, barWidth * (i + 1), height(), Qt::red);
              // clear the rest of the control
              painter.fillRect(barWidth * i, 0, barWidth * (i + 1), height() - h, Qt::black);
          }
      }

      void FrameProcessor::processFrame(QVideoFrame frame, int levels)
      {
          QVector<qreal> histogram(levels);

          do {
              if (!levels)
                  break;

              if (!frame.map(QAbstractVideoBuffer::ReadOnly))
                  break;

              if (frame.pixelFormat() == QVideoFrame::Format_YUV420P ||
                  frame.pixelFormat() == QVideoFrame::Format_NV12) {
                  // Process YUV data
                  uchar *b = frame.bits();
                  for (int y = 0; y < frame.height(); y++) {
                      uchar *lastPixel = b + frame.width();
                      for (uchar *curPixel = b; curPixel < lastPixel; curPixel++)
                          histogram[(*curPixel * levels) >> 8] += 1.0;
                      b += frame.bytesPerLine();
                  }
              } else {
                  QImage::Format imageFormat = QVideoFrame::imageFormatFromPixelFormat(frame.pixelFormat());
                  if (imageFormat != QImage::Format_Invalid) {
                      // Process RGB data
                      QImage image(frame.bits(), frame.width(), frame.height(), imageFormat);
                      image = image.convertToFormat(QImage::Format_RGB32);

                      const QRgb* b = (const QRgb*)image.bits();
                      for (int y = 0; y < image.height(); y++) {
                          const QRgb *lastPixel = b + frame.width();
                          for (const QRgb *curPixel = b; curPixel < lastPixel; curPixel++)
                              histogram[(qGray(*curPixel) * levels) >> 8] += 1.0;
                          b = (const QRgb*)((uchar*)b + image.bytesPerLine());
                      }
                  }
              }

              // find maximum value
              qreal maxValue = 0.0;
              for (int i = 0; i < histogram.size(); i++) {
                  if (histogram[i] > maxValue)
                      maxValue = histogram[i];
              }

              if (maxValue > 0.0) {
                  for (int i = 0; i < histogram.size(); i++)
                      histogram[i] /= maxValue;
              }

              frame.unmap();
          } while (false);

          emit histogramReady(histogram);
      }