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>

2 files changed, 79 insertions, 36 deletions

diff --git a/examples/player/histogramwidget.cpp b/examples/player/histogramwidget.cpp
index cf7ae6fff..d9327519e 100644
--- a/examples/player/histogramwidget.cpp
+++ b/examples/player/histogramwidget.cpp
@@ -44,29 +44,78 @@
 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
+
+    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 (!m_levels)
+        if (!levels)
             break;
 
         if (!frame.map(QAbstractVideoBuffer::ReadOnly))
             break;
 
-        m_histogram.resize(m_levels);
-
-        if (frame.pixelFormat() == QVideoFrame::Format_YUV420P) {
-            // Process YUV420P data
+        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++)
-                    m_histogram[(*curPixel * m_levels) / 256] += 1.0;
+                    histogram[(*curPixel * levels) >> 8] += 1.0;
                 b += frame.bytesPerLine();
             }
         } else {
@@ -80,7 +129,7 @@ void HistogramWidget::processFrame(QVideoFrame frame)
                 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;
+                        histogram[(qGray(*curPixel) * levels) >> 8] += 1.0;
                     b = (const QRgb*)((uchar*)b + image.bytesPerLine());
                 }
             }
@@ -88,40 +137,18 @@ void HistogramWidget::processFrame(QVideoFrame frame)
 
         // find maximum value
         qreal maxValue = 0.0;
-        for (int i = 0; i < m_histogram.size(); i++) {
-            if (m_histogram[i] > maxValue)
-                maxValue = m_histogram[i];
+        for (int i = 0; i < histogram.size(); i++) {
+            if (histogram[i] > maxValue)
+                maxValue = histogram[i];
         }
 
         if (maxValue > 0.0) {
-            for (int i = 0; i < m_histogram.size(); i++)
-                m_histogram[i] /= maxValue;
+            for (int i = 0; i < histogram.size(); i++)
+                histogram[i] /= maxValue;
         }
 
         frame.unmap();
     } while (false);
 
-    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);
-    }
+    emit histogramReady(histogram);
 }
diff --git a/examples/player/histogramwidget.h b/examples/player/histogramwidget.h
index 2d1883fff..d15b84113 100644
--- a/examples/player/histogramwidget.h
+++ b/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