Player example histogram: Process frames on a separate thread

Change-Id: I6989f9ea9cb6e45c54ed75079a5b5748e15ee0d8
Reviewed-by: Dmytro Poplavskiy <dmytro.poplavskiy@nokia.com>
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

examples/player/histogramwidget.cpp

@@ -44,63 +44,34 @@
 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)
 {
-    m_histogram.clear();
+    if (m_isBusy)
+        return; //drop frame
 
-    do {
+    m_isBusy = true;
-        if (!m_levels)
+    QMetaObject::invokeMethod(&m_processor, "processFrame",
-            break;
+                              Qt::QueuedConnection, Q_ARG(QVideoFrame, frame), Q_ARG(int, m_levels));
-
-        if (!frame.map(QAbstractVideoBuffer::ReadOnly))
-            break;
-
-        m_histogram.resize(m_levels);
-
-        if (frame.pixelFormat() == QVideoFrame::Format_YUV420P) {
-            // Process YUV420P 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++)
-                    m_histogram[(*curPixel * m_levels) / 256] += 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++)
-                        m_histogram[(qGray(*curPixel) * m_levels) / 256] += 1.0;
-                    b = (const QRgb*)((uchar*)b + image.bytesPerLine());
-                }
-            }
 }
 
-        // find maximum value
+void HistogramWidget::setHistogram(QVector<qreal> histogram)
-        qreal maxValue = 0.0;
+{
-        for (int i = 0; i < m_histogram.size(); i++) {
+    m_isBusy = false;
-            if (m_histogram[i] > maxValue)
+    m_histogram = histogram;
-                maxValue = m_histogram[i];
-        }
-
-        if (maxValue > 0.0) {
-            for (int i = 0; i < m_histogram.size(); i++)
-                m_histogram[i] /= maxValue;
-        }
-
-        frame.unmap();
-    } while (false);
-
     update();
 }
 
@@ -125,3 +96,59 @@ void HistogramWidget::paintEvent(QPaintEvent *event)
         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);
+}

examples/player/histogramwidget.h

@@ -43,18 +43,31 @@
 
 #include <QWidget>
 #include <qvideoframe.h>
+#include <QThread>
 
 QT_USE_NAMESPACE
 
+class FrameProcessor: public QObject {
+    Q_OBJECT
+
+public slots:
+    void processFrame(QVideoFrame frame, int levels);
+
+signals:
+    void histogramReady(QVector<qreal> histogram);
+};
+
 class HistogramWidget : public QWidget
 {
     Q_OBJECT
 public:
     explicit HistogramWidget(QWidget *parent = 0);
+    ~HistogramWidget();
     void setLevels(int levels) { m_levels = levels; }
 
 public slots:
     void processFrame(QVideoFrame frame);
+    void setHistogram(QVector<qreal> histogram);
 
 protected:
     void paintEvent(QPaintEvent *event);
@@ -62,6 +75,9 @@ protected:
 private:
     QVector<qreal> m_histogram;
     int m_levels;
+    FrameProcessor m_processor;
+    QThread m_processorThread;
+    bool m_isBusy;
 };
 
 #endif // HISTOGRAMWIDGET_H