Qt 5.7 | Qt Data Visualization | Audiolevels Example | audiolevelsiodevice.cpp Example File

Qt 5.7.1 Reference Documentation

# audiolevelsiodevice.cpp Example File

audiolevels/audiolevelsiodevice.cpp

      /****************************************************************************
      **
      ** Copyright (C) 2016 The Qt Company Ltd.
      ** Contact: https://www.qt.io/licensing/
      **
      ** This file is part of the Qt Data Visualization module of the Qt Toolkit.
      **
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      ** Alternatively, this file may be used under the terms of the GNU
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      ** the Free Software Foundation and appearing in the file LICENSE.GPL3
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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;
      }