1 files changed, 54 insertions, 0 deletions
diff --git a/examples/multimedia/spectrum/tonegenerator.cpp b/examples/multimedia/spectrum/tonegenerator.cpp
new file mode 100644
index 000000000..5df1df44d
--- /dev/null
+++ b/examples/multimedia/spectrum/tonegenerator.cpp
@@ -0,0 +1,54 @@
+// Copyright (C) 2017 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "spectrum.h"
+#include "utils.h"
+
+#include <QAudioFormat>
+#include <QByteArray>
+#include <QtEndian>
+#include <QtMath>
+
+void generateTone(const SweptTone &tone, const QAudioFormat &format, QByteArray &buffer)
+{
+    Q_ASSERT(format.sampleFormat() == QAudioFormat::Int16);
+
+    const int channelBytes = format.bytesPerSample();
+    const int sampleBytes = format.channelCount() * channelBytes;
+    int length = buffer.size();
+    const int numSamples = buffer.size() / sampleBytes;
+
+    Q_ASSERT(length % sampleBytes == 0);
+    Q_UNUSED(sampleBytes); // suppress warning in release builds
+
+    unsigned char *ptr = reinterpret_cast<unsigned char *>(buffer.data());
+
+    qreal phase = 0.0;
+
+    const qreal d = 2 * M_PI / format.sampleRate();
+
+    // We can't generate a zero-frequency sine wave
+    const qreal startFreq = tone.startFreq ? tone.startFreq : 1.0;
+
+    // Amount by which phase increases on each sample
+    qreal phaseStep = d * startFreq;
+
+    // Amount by which phaseStep increases on each sample
+    // If this is non-zero, the output is a frequency-swept tone
+    const qreal phaseStepStep = d * (tone.endFreq - startFreq) / numSamples;
+
+    while (length) {
+        const qreal x = tone.amplitude * qSin(phase);
+        const qint16 value = realToPcm(x);
+        for (int i = 0; i < format.channelCount(); ++i) {
+            qToLittleEndian<qint16>(value, ptr);
+            ptr += channelBytes;
+            length -= channelBytes;
+        }
+
+        phase += phaseStep;
+        while (phase > 2 * M_PI)
+            phase -= 2 * M_PI;
+        phaseStep += phaseStepStep;
+    }
+}