- Qt 5.3
- Qt Multimedia Widgets
- Media Player Example
- histogramwidget.cpp Example File
- Qt 5.3.2 Reference Documentation

# histogramwidget.cpp Example File

player/histogramwidget.cpp

    /****************************************************************************
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    ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
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    ** This file is part of the examples of the Qt Toolkit.
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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);
    }