audiolevelsiodevice.cpp Example File

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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;
  }