Polish the audio example

- Use C++ 11 (nullptr, override)
- Bail out cleanly if there is no audio input available
- Rewrite the buffer algorithm to work on a member
  variable to make the slidling window principle
  clearer and reduce QVector allocations

Task-number: QTBUG-60662
Change-Id: I02827f3dca4f0bf1fb213fa12369455de6c618c5
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>

5 files changed, 60 insertions, 42 deletions

diff --git a/examples/charts/audio/main.cpp b/examples/charts/audio/main.cpp
index be287d7b..8c4eca66 100644
--- a/examples/charts/audio/main.cpp
+++ b/examples/charts/audio/main.cpp
@@ -27,13 +27,24 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets/QApplication>
 #include "widget.h"
 
+#include <QtMultimedia/QAudioDeviceInfo>
+#include <QtWidgets/QApplication>
+#include <QtWidgets/QMessageBox>
+
 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);
-    Widget w;
+
+    const QAudioDeviceInfo inputDevice = QAudioDeviceInfo::defaultInputDevice();
+    if (inputDevice.isNull()) {
+        QMessageBox::warning(nullptr, "audio",
+                             "There is no audio input device available.");
+        return -1;
+    }
+
+    Widget w(inputDevice);
     w.show();
     
     return a.exec();
diff --git a/examples/charts/audio/widget.cpp b/examples/charts/audio/widget.cpp
index b285a6ca..86dd6206 100644
--- a/examples/charts/audio/widget.cpp
+++ b/examples/charts/audio/widget.cpp
@@ -28,31 +28,30 @@
 ****************************************************************************/
 
 #include "widget.h"
+#include "xyseriesiodevice.h"
+
 #include <QtMultimedia/QAudioDeviceInfo>
 #include <QtMultimedia/QAudioInput>
+
 #include <QtCharts/QChartView>
 #include <QtCharts/QLineSeries>
 #include <QtCharts/QChart>
-#include <QtWidgets/QVBoxLayout>
 #include <QtCharts/QValueAxis>
-#include "xyseriesiodevice.h"
+
+#include <QtWidgets/QVBoxLayout>
 
 QT_CHARTS_USE_NAMESPACE
 
-Widget::Widget(QWidget *parent)
-    : QWidget(parent),
-      m_device(0),
-      m_chart(0),
-      m_series(0),
-      m_audioInput(0)
+Widget::Widget(const QAudioDeviceInfo &deviceInfo, QWidget *parent) :
+    QWidget(parent),
+    m_chart(new QChart),
+    m_series(new QLineSeries)
 {
-    m_chart = new QChart;
     QChartView *chartView = new QChartView(m_chart);
     chartView->setMinimumSize(800, 600);
-    m_series = new QLineSeries;
     m_chart->addSeries(m_series);
     QValueAxis *axisX = new QValueAxis;
-    axisX->setRange(0, 2000);
+    axisX->setRange(0, XYSeriesIODevice::sampleCount);
     axisX->setLabelFormat("%g");
     axisX->setTitleText("Samples");
     QValueAxis *axisY = new QValueAxis;
@@ -61,11 +60,10 @@ Widget::Widget(QWidget *parent)
     m_chart->setAxisX(axisX, m_series);
     m_chart->setAxisY(axisY, m_series);
     m_chart->legend()->hide();
-    m_chart->setTitle("Data from the microphone");
+    m_chart->setTitle("Data from the microphone (" + deviceInfo.deviceName() + ')');
 
-    QVBoxLayout *mainLayout = new QVBoxLayout;
+    QVBoxLayout *mainLayout = new QVBoxLayout(this);
     mainLayout->addWidget(chartView);
-    setLayout(mainLayout);
 
     QAudioFormat formatAudio;
     formatAudio.setSampleRate(8000);
@@ -75,8 +73,7 @@ Widget::Widget(QWidget *parent)
     formatAudio.setByteOrder(QAudioFormat::LittleEndian);
     formatAudio.setSampleType(QAudioFormat::UnSignedInt);
 
-    QAudioDeviceInfo inputDevices = QAudioDeviceInfo::defaultInputDevice();
-    m_audioInput = new QAudioInput(inputDevices,formatAudio, this);
+    m_audioInput = new QAudioInput(deviceInfo, formatAudio, this);
 
     m_device = new XYSeriesIODevice(m_series, this);
     m_device->open(QIODevice::WriteOnly);
diff --git a/examples/charts/audio/widget.h b/examples/charts/audio/widget.h
index 70cc3862..82072b92 100644
--- a/examples/charts/audio/widget.h
+++ b/examples/charts/audio/widget.h
@@ -44,6 +44,7 @@ class XYSeriesIODevice;
 
 QT_BEGIN_NAMESPACE
 class QAudioInput;
+class QAudioDeviceInfo;
 QT_END_NAMESPACE
 
 class Widget : public QWidget
@@ -51,14 +52,14 @@ class Widget : public QWidget
     Q_OBJECT
 
 public:
-    Widget(QWidget *parent = 0);
+    explicit Widget(const QAudioDeviceInfo &deviceInfo, QWidget *parent = nullptr);
     ~Widget();
 
 private:
-    XYSeriesIODevice *m_device;
+    XYSeriesIODevice *m_device = nullptr;
     QChart *m_chart;
-    QLineSeries *m_series;
-    QAudioInput *m_audioInput;
+    QLineSeries *m_series ;
+    QAudioInput *m_audioInput = nullptr;
 };
 
 #endif // WIDGET_H
diff --git a/examples/charts/audio/xyseriesiodevice.cpp b/examples/charts/audio/xyseriesiodevice.cpp
index 19669ff9..d129725d 100644
--- a/examples/charts/audio/xyseriesiodevice.cpp
+++ b/examples/charts/audio/xyseriesiodevice.cpp
@@ -28,39 +28,43 @@
 ****************************************************************************/
 
 #include "xyseriesiodevice.h"
+
 #include <QtCharts/QXYSeries>
 
-XYSeriesIODevice::XYSeriesIODevice(QXYSeries * series, QObject *parent) :
+XYSeriesIODevice::XYSeriesIODevice(QXYSeries *series, QObject *parent) :
     QIODevice(parent),
     m_series(series)
 {
 }
 
-qint64 XYSeriesIODevice::readData(char * data, qint64 maxSize)
+qint64 XYSeriesIODevice::readData(char *data, qint64 maxSize)
 {
     Q_UNUSED(data)
     Q_UNUSED(maxSize)
     return -1;
 }
 
-qint64 XYSeriesIODevice::writeData(const char * data, qint64 maxSize)
+qint64 XYSeriesIODevice::writeData(const char *data, qint64 maxSize)
 {
-    qint64 range = 2000;
-    QVector<QPointF> oldPoints = m_series->pointsVector();
-    QVector<QPointF> points;
-    int resolution = 4;
+    static const int resolution = 4;
+
+    if (m_buffer.isEmpty()) {
+        m_buffer.reserve(sampleCount);
+        for (int i = 0; i < sampleCount; ++i)
+            m_buffer.append(QPointF(i, 0));
+    }
 
-    if (oldPoints.count() < range) {
-        points = m_series->pointsVector();
-    } else {
-        for (int i = maxSize/resolution; i < oldPoints.count(); i++)
-            points.append(QPointF(i - maxSize/resolution, oldPoints.at(i).y()));
+    int start = 0;
+    const int availableSamples = int(maxSize) / resolution;
+    if (availableSamples < sampleCount) {
+        start = sampleCount - availableSamples;
+        for (int s = 0; s < start; ++s)
+            m_buffer[s].setY(m_buffer.at(s + availableSamples).y());
     }
 
-    qint64 size = points.count();
-    for (int k = 0; k < maxSize/resolution; k++)
-        points.append(QPointF(k + size, ((quint8)data[resolution * k] - 128)/128.0));
+    for (int s = start; s < sampleCount; ++s, data += resolution)
+        m_buffer[s].setY(qreal(uchar(*data) -128) / qreal(128));
 
-    m_series->replace(points);
-    return maxSize;
+    m_series->replace(m_buffer);
+    return (sampleCount - start) * resolution;
 }
diff --git a/examples/charts/audio/xyseriesiodevice.h b/examples/charts/audio/xyseriesiodevice.h
index 05daf974..cbbf2271 100644
--- a/examples/charts/audio/xyseriesiodevice.h
+++ b/examples/charts/audio/xyseriesiodevice.h
@@ -31,6 +31,8 @@
 #define XYSERIESIODEVICE_H
 
 #include <QtCore/QIODevice>
+#include <QtCore/QPointF>
+#include <QtCore/QVector>
 #include <QtCharts/QChartGlobal>
 
 QT_CHARTS_BEGIN_NAMESPACE
@@ -43,14 +45,17 @@ class XYSeriesIODevice : public QIODevice
 {
     Q_OBJECT
 public:
-    explicit XYSeriesIODevice(QXYSeries * series, QObject *parent = 0);
+    explicit XYSeriesIODevice(QXYSeries *series, QObject *parent = nullptr);
+
+    static const int sampleCount = 2000;
 
 protected:
-    qint64 readData(char * data, qint64 maxSize);
-    qint64 writeData(const char * data, qint64 maxSize);
+    qint64 readData(char *data, qint64 maxSize) override;
+    qint64 writeData(const char *data, qint64 maxSize) override;
 
 private:
     QXYSeries *m_series;
+    QVector<QPointF> m_buffer;
 };
 
 #endif // XYSERIESIODEVICE_H