audiolevelsiodevice.cpp Example File

audiolevels/audiolevelsiodevice.cpp
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 #include "audiolevelsiodevice.h"
 #include <QtCore/QDebug>

 using namespace QtDataVisualization;

 static const int resolution = 8;
 static const int rowSize = 800;
 static const int rowCount = 7; // Must be odd number
 static const int middleRow = rowCount / 2;

 AudioLevelsIODevice::AudioLevelsIODevice(QBarDataProxy *proxy, QObject *parent)
     : QIODevice(parent),
       m_proxy(proxy),
       m_array(new QBarDataArray)
 {
     // We reuse the existing array for maximum performance, so construct the array here
     m_array->reserve(rowCount);
     for (int i = 0; i < rowCount; i++)
         m_array->append(new QBarDataRow(rowSize));

     qDebug() << "Total of" << (rowSize * rowCount) << "items in the array.";
 }

 // Implementation required for this pure virtual function
 qint64 AudioLevelsIODevice::readData(char *data, qint64 maxSize)
 {
     Q_UNUSED(data)
     Q_UNUSED(maxSize)
     return -1;
 }

 qint64 AudioLevelsIODevice::writeData(const char *data, qint64 maxSize)
 {
     // The amount of new data available.
     int newDataSize = maxSize / resolution;

     // If we get more data than array size, we need to adjust the start index for new data.
     int newDataStartIndex = qMax(0, (newDataSize - rowSize));

     // Move the old data ahead in the rows (only do first half of rows + middle one now).
     // If the amount of new data was larger than row size, skip copying.
     if (!newDataStartIndex) {
         for (int i = 0; i <= middleRow; i++) {
             QBarDataItem *srcPos = m_array->at(i)->data();
             QBarDataItem *dstPos = srcPos + newDataSize;
             memmove((void *)dstPos, (void *)srcPos, (rowSize - newDataSize) * sizeof(QBarDataItem));
         }
     }

     // Insert data in reverse order, so that newest data is always at the front of the row.
     int index = 0;
     for (int i = newDataSize - 1; i >= newDataStartIndex; i--) {
         // Add 0.01 to the value to avoid gaps in the graph (i.e. zero height bars).
         // Also, scale to 0...100
         float value = float(quint8(data[resolution * i]) - 128) / 1.28f + 0.01f;
         (*m_array->at(middleRow))[index].setValue(value);
         // Insert a fractional value into front half of the rows.
         for (int j = 1; j <= middleRow; j++) {
             float fractionalValue = value / float(j + 1);
             (*m_array->at(middleRow - j))[index].setValue(fractionalValue);
         }
         index++;
     }

     // Copy the front half of rows to the back half for symmetry.
     index = 0;
     for (int i = rowCount - 1; i > middleRow; i--) {
         QBarDataItem *srcPos = m_array->at(index++)->data();
         QBarDataItem *dstPos = m_array->at(i)->data();
         memcpy((void *)dstPos, (void *)srcPos, rowSize * sizeof(QBarDataItem));
     }

     // Reset the proxy array now that data has been updated to trigger a redraw.
     m_proxy->resetArray(m_array);

     return maxSize;
 }