Play whole file in spectrum analyzer demo

This change required a significant refactoring of the application,
including:

* Re-write WavFile class so that it inherits from QFile rather
  than taking a QIODevice as an argument to its method calls.

* Modified Engine class so that its internal QByteArray buffer
  (m_buffer) need not correspond to the entire clip.  This was done
  by introducing the m_bufferPosition variable, which indicates the
  offset from the start of the clip to the start of the region of
  the clip which is currently held in memory.  For tone generation
  and record/playback modes, the buffer does still map directly to
  the whole clip, so m_bufferPosition is always zero.  For file
  playback, the WavFile instance is the QIODevice which is passed
  to QAudioOutput; m_buffer is just the part of the file which is
  currently in memory for spectrum analysis, level calculation and
  waveform rendering.

* For file playback, introduced a second WavFile instance as a
  member of the Engine class.  This is because QFile::seek() is
  called in order to read the part of the file currently required
  for analysis.  If the QAudioOutput implementation passes its
  QIODevice across a thread boundary, this seeking causes playback
  to jump around within the file rather than progressing smoothly
  forward.

* Modified the audioLength utility function so that its return
  value is always a multiple of the sample size.

In the process of making the above changes, a few other minor
modifications were made:

* Modify all internal APIs concerned with buffer offsets and lengths
  to deal in bytes.  Previously, some calls passed values in
  microseconds and others in bytes, which was confusing.

* Remove write functionality from WavFile class, since it is not
  used in this application.

Task-number: QTBUG-12936

1 files changed, 50 insertions, 155 deletions

diff --git a/demos/spectrum/app/wavfile.cpp b/demos/spectrum/app/wavfile.cpp
index 74d5918..44c3ac5 100644
--- a/demos/spectrum/app/wavfile.cpp
+++ b/demos/spectrum/app/wavfile.cpp
@@ -78,179 +78,74 @@ struct CombinedHeader
     WAVEHeader  wave;
 };
 
-
-
-WavFile::WavFile(const QAudioFormat &format, qint64 dataLength)
-    : m_format(format)
-    , m_dataLength(dataLength)
-    , m_dataPosition(0)
-{
-}
-
-bool WavFile::readHeader(QIODevice &device)
-{
-    if (!device.isSequential()) {
-        if (!device.seek(0))
-            return false;
-        // XXX: else, assume that current position is the start of the header
-    }
-
-    CombinedHeader header;
-    if (device.read(reinterpret_cast<char *>(&header), sizeof(CombinedHeader)) != sizeof(CombinedHeader))
-        return false;
-
-    if ((memcmp(&header.riff.descriptor.id, "RIFF", 4) == 0
-        || memcmp(&header.riff.descriptor.id, "RIFX", 4) == 0)
-        && memcmp(&header.riff.type, "WAVE", 4) == 0
-        && memcmp(&header.wave.descriptor.id, "fmt ", 4) == 0
-        && (header.wave.audioFormat == 1 || header.wave.audioFormat == 0)) {
-
-        // Read off remaining header information
-        DATAHeader dataHeader;
-
-        if (qFromLittleEndian<quint32>(header.wave.descriptor.size) > sizeof(WAVEHeader)) {
-            // Extended data available
-            quint16 extraFormatBytes;
-            if (device.peek((char*)&extraFormatBytes, sizeof(quint16)) != sizeof(quint16))
-                return false;
-            const qint64 throwAwayBytes = sizeof(quint16) + qFromLittleEndian<quint16>(extraFormatBytes);
-            if (device.read(throwAwayBytes).size() != throwAwayBytes)
-                return false;
-        }
-
-        if (device.read((char*)&dataHeader, sizeof(DATAHeader)) != sizeof(DATAHeader))
-            return false;
-
-        // Establish format
-        if (memcmp(&header.riff.descriptor.id, "RIFF", 4) == 0)
-            m_format.setByteOrder(QAudioFormat::LittleEndian);
-        else
-            m_format.setByteOrder(QAudioFormat::BigEndian);
-
-        int bps = qFromLittleEndian<quint16>(header.wave.bitsPerSample);
-        m_format.setChannels(qFromLittleEndian<quint16>(header.wave.numChannels));
-        m_format.setCodec("audio/pcm");
-        m_format.setFrequency(qFromLittleEndian<quint32>(header.wave.sampleRate));
-        m_format.setSampleSize(qFromLittleEndian<quint16>(header.wave.bitsPerSample));
-        m_format.setSampleType(bps == 8 ? QAudioFormat::UnSignedInt : QAudioFormat::SignedInt);
-
-        m_dataLength = qFromLittleEndian<quint32>(dataHeader.descriptor.size);
-        m_dataPosition = 0;
-    }
-
-    return true;
-}
-
-bool WavFile::writeHeader(QIODevice &device)
+WavFile::WavFile(QObject *parent)
+    : QFile(parent)
+    , m_headerLength(0)
 {
-    CombinedHeader header;
-    DATAHeader dataHeader;
-
-    memset(&header, 0, sizeof(CombinedHeader));
-
-    // RIFF header
-    if (m_format.byteOrder() == QAudioFormat::LittleEndian)
-        strncpy(&header.riff.descriptor.id[0], "RIFF", 4);
-    else
-        strncpy(&header.riff.descriptor.id[0], "RIFX", 4);
-    qToLittleEndian<quint32>(quint32(m_dataLength + sizeof(CombinedHeader) + sizeof(DATAHeader) - sizeof(chunk)),
-                             reinterpret_cast<unsigned char*>(&header.riff.descriptor.size));
-    strncpy(&header.riff.type[0], "WAVE", 4);
-
-    // WAVE header
-    strncpy(&header.wave.descriptor.id[0], "fmt ", 4);
-    qToLittleEndian<quint32>(quint32(16),
-                             reinterpret_cast<unsigned char*>(&header.wave.descriptor.size));
-    qToLittleEndian<quint16>(quint16(1),
-                             reinterpret_cast<unsigned char*>(&header.wave.audioFormat));
-    qToLittleEndian<quint16>(quint16(m_format.channels()),
-                             reinterpret_cast<unsigned char*>(&header.wave.numChannels));
-    qToLittleEndian<quint32>(quint32(m_format.frequency()),
-                             reinterpret_cast<unsigned char*>(&header.wave.sampleRate));
-    qToLittleEndian<quint32>(quint32(m_format.frequency() * m_format.channels() * m_format.sampleSize() / 8),
-                             reinterpret_cast<unsigned char*>(&header.wave.byteRate));
-    qToLittleEndian<quint16>(quint16(m_format.channels() * m_format.sampleSize() / 8),
-                             reinterpret_cast<unsigned char*>(&header.wave.blockAlign));
-    qToLittleEndian<quint16>(quint16(m_format.sampleSize()),
-                             reinterpret_cast<unsigned char*>(&header.wave.bitsPerSample));
-
-    // DATA header
-    strncpy(dataHeader.descriptor.id, "data", 4);
-    qToLittleEndian<quint32>(quint32(m_dataLength),
-                             reinterpret_cast<unsigned char*>(&dataHeader.descriptor.size));
 
-    return device.write(reinterpret_cast<const char *>(&header), sizeof(CombinedHeader)) == sizeof(CombinedHeader)
-           && device.write(reinterpret_cast<const char*>(&dataHeader), sizeof(DATAHeader)) == sizeof(DATAHeader);
 }
 
-const QAudioFormat& WavFile::format() const
+bool WavFile::open(const QString &fileName)
 {
-    return m_format;
+    close();
+    setFileName(fileName);
+    return QFile::open(QIODevice::ReadOnly) && readHeader();
 }
 
-qint64 WavFile::dataLength() const
+const QAudioFormat &WavFile::fileFormat() const
 {
-    return m_dataLength;
+    return m_fileFormat;
 }
 
-qint64 WavFile::headerLength()
+qint64 WavFile::headerLength() const
 {
-    return sizeof(CombinedHeader);
-}
-
-bool WavFile::writeDataLength(QIODevice &device, qint64 dataLength)
-{
-    bool result = false;
-    if (!device.isSequential()) {
-        device.seek(40);
-        unsigned char dataLengthLE[4];
-        qToLittleEndian<quint32>(quint32(dataLength), dataLengthLE);
-        result = (device.write(reinterpret_cast<const char *>(dataLengthLE), 4) == 4);
-    }
-    return result;
+return m_headerLength;
 }
 
-qint64 WavFile::readData(QIODevice &device, QByteArray &buffer,
-                         QAudioFormat outputFormat)
+bool WavFile::readHeader()
 {
-    // Sanity checks
-    if (!outputFormat.isValid())
-        outputFormat = m_format;
-
-    if (!isPCMS16LE(outputFormat) || !isPCMS16LE(m_format))
-        return 0;
-
-    if (m_dataPosition == m_dataLength)
-        return 0;
-
-    // Process
-    qint64 result = 0;
-
-    const int frameSize = 2 * m_format.channels(); // 16 bit samples
-    QVector<char> inputSample(frameSize);
-
-    qint16 *output = reinterpret_cast<qint16*>(buffer.data());
+    seek(0);
+    CombinedHeader header;
+    bool result = read(reinterpret_cast<char *>(&header), sizeof(CombinedHeader)) == sizeof(CombinedHeader);
+    if (result) {
+        if ((memcmp(&header.riff.descriptor.id, "RIFF", 4) == 0
+            || memcmp(&header.riff.descriptor.id, "RIFX", 4) == 0)
+            && memcmp(&header.riff.type, "WAVE", 4) == 0
+            && memcmp(&header.wave.descriptor.id, "fmt ", 4) == 0
+            && (header.wave.audioFormat == 1 || header.wave.audioFormat == 0)) {
+
+            // Read off remaining header information
+            DATAHeader dataHeader;
+
+            if (qFromLittleEndian<quint32>(header.wave.descriptor.size) > sizeof(WAVEHeader)) {
+                // Extended data available
+                quint16 extraFormatBytes;
+                if (peek((char*)&extraFormatBytes, sizeof(quint16)) != sizeof(quint16))
+                    return false;
+                const qint64 throwAwayBytes = sizeof(quint16) + qFromLittleEndian<quint16>(extraFormatBytes);
+                if (read(throwAwayBytes).size() != throwAwayBytes)
+                    return false;
+            }
 
-    while (result < buffer.size()) {
-        if (m_dataPosition == m_dataLength)
-            break;
+            if (read((char*)&dataHeader, sizeof(DATAHeader)) != sizeof(DATAHeader))
+                return false;
 
-        // XXX only working with particular alignments
-        if (device.read(inputSample.data(), inputSample.count())) {
-            int inputIdx = 0;
-            for (int outputIdx = 0; outputIdx < outputFormat.channels(); ++outputIdx) {
-                const qint16* input = reinterpret_cast<const qint16*>(inputSample.data() + 2 * inputIdx);
-                *output++ = qFromLittleEndian<qint16>(*input);
-                result += 2;
-                if (inputIdx < m_format.channels())
-                    ++inputIdx;
-            }
-            m_dataPosition += frameSize;
+            // Establish format
+            if (memcmp(&header.riff.descriptor.id, "RIFF", 4) == 0)
+                m_fileFormat.setByteOrder(QAudioFormat::LittleEndian);
+            else
+                m_fileFormat.setByteOrder(QAudioFormat::BigEndian);
+
+            int bps = qFromLittleEndian<quint16>(header.wave.bitsPerSample);
+            m_fileFormat.setChannels(qFromLittleEndian<quint16>(header.wave.numChannels));
+            m_fileFormat.setCodec("audio/pcm");
+            m_fileFormat.setFrequency(qFromLittleEndian<quint32>(header.wave.sampleRate));
+            m_fileFormat.setSampleSize(qFromLittleEndian<quint16>(header.wave.bitsPerSample));
+            m_fileFormat.setSampleType(bps == 8 ? QAudioFormat::UnSignedInt : QAudioFormat::SignedInt);
         } else {
-            break;
+            result = false;
         }
     }
-
+    m_headerLength = pos();
     return result;
 }
-