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diff --git a/examples/datavisualization/audiolevels/doc/src/audiolevels.qdoc b/examples/datavisualization/audiolevels/doc/src/audiolevels.qdoc new file mode 100644 index 00000000..ad87ecc0 --- /dev/null +++ b/examples/datavisualization/audiolevels/doc/src/audiolevels.qdoc @@ -0,0 +1,85 @@ +/**************************************************************************** +** +** Copyright (C) 2014 Digia Plc +** All rights reserved. +** For any questions to Digia, please use contact form at http://qt.digia.com +** +** This file is part of the QtDataVisualization module. +** +** Licensees holding valid Qt Enterprise licenses may use this file in +** accordance with the Qt Enterprise License Agreement provided with the +** Software or, alternatively, in accordance with the terms contained in +** a written agreement between you and Digia. +** +** If you have questions regarding the use of this file, please use +** contact form at http://qt.digia.com +** +****************************************************************************/ + +/*! + \example audiolevels + \title Audiolevels Example + \ingroup qtdatavisualization_examples + \brief Simple application showing real time audio data. + + The audiolevels example shows how feed real-time dynamic data to a graph using Q3DBars. + + This example reads the audio levels from a microphone and displays those levels + in a bar graph. To increase the load for demonstration purposes, and to make the + graph little fancier, slightly modified data is used to fill multiple rows. + + \image audiolevels-example.png + + The interesting stuff happens in \c AudioLevels and \c AudioLevelsIODevice classes, so we + concentrate on those and skip explaining the basic Q3DBars functionality - for that see + \l{Bars Example}. + + \c AudioLevelsIODevice subclasses QIODevice and is given as input device for QAudioInput + class, so it receives microphone data. + + In the header file for \c AudioLevels class we declare necessary members: + + \snippet ../examples/audiolevels/audiolevels.h 0 + + And initialize the microphone listening in the source: + + \snippet ../examples/audiolevels/audiolevels.cpp 0 + + In the header file for \c AudioLevelsIODevice class we store pointers to the data proxy and + also the data array we give to the proxy, because we reuse the same array to keep memory + reallocations to the minimum: + + \snippet ../examples/audiolevels/audiolevelsiodevice.h 0 + + In the source file we define some static constants to define size of the data array and + the middle row index, as well as the resolution of the visualization. You may need to adjust + these values to get decent performance in low-end devices: + + \snippet ../examples/audiolevels/audiolevelsiodevice.cpp 1 + + The \c resolution constant indicates the sample rate, for example, value 8 means every eighth + byte from audio input is visualized. This is necessary to make the data readable, as it would + otherwise make the graph scroll too fast. + + In the \c AudioLevelsIODevice class constructor we initialize the data array: + + \snippet ../examples/audiolevels/audiolevelsiodevice.cpp 0 + + The \c AudioLevelsIODevice::writeData function is called whenever there is new audio data + available to be visualized. There we move the old data along the rows and insert new + data in the beginning of the rows: + + \snippet ../examples/audiolevels/audiolevelsiodevice.cpp 2 + + We use a couple of techniques here to improve performance. First, we reuse + the existing data array, as this allows us to avoid any extra memory allocations in our + application code. This also means the data array dimensions do not change, which further + improves efficiency in the bar graph renderer. + Secondly, since each row is a QVector of bar data items, which do not allocate any data that needs + deletion, we can utilize \c memmove and \c memcpy functions to quickly move and copy data around. + + \note In the future versions of Qt Data Visualization, QBarDataItem might get extended so that + it does allocate some memory to store other optional bar properties besides the value. + In use cases where those optional properties are used, using \c memmove and \c memcpy could lead to + memory leaks, so use them with care. +*/ |