Added a simple spectrogram example app.

examples/SimpleFFTExample/Source/Main.cpp

@@ -0,0 +1,80 @@
+/*
+  ==============================================================================
+
+    JUCE demo code - use at your own risk!
+
+  ==============================================================================
+*/
+
+#include "../JuceLibraryCode/JuceHeader.h"
+#include "SpectrogramComponent.h"
+
+
+//==============================================================================
+class SimpleFFTExampleApplication  : public JUCEApplication
+{
+public:
+    //==============================================================================
+    SimpleFFTExampleApplication() {}
+
+    const String getApplicationName() override       { return ProjectInfo::projectName; }
+    const String getApplicationVersion() override    { return ProjectInfo::versionString; }
+    bool moreThanOneInstanceAllowed() override       { return true; }
+
+    //==============================================================================
+    void initialise (const String& /*commandLine*/) override
+    {
+        mainWindow = new MainWindow();
+    }
+
+    void shutdown() override
+    {
+        mainWindow = nullptr; // (deletes our window)
+    }
+
+    //==============================================================================
+    void systemRequestedQuit() override
+    {
+        // This is called when the app is being asked to quit: you can ignore this
+        // request and let the app carry on running, or call quit() to allow the app to close.
+        quit();
+    }
+
+    //==============================================================================
+    /*
+        This class implements the desktop window that contains an instance of
+        our MainContentComponent class.
+    */
+    class MainWindow    : public DocumentWindow
+    {
+    public:
+        MainWindow()  : DocumentWindow (ProjectInfo::projectName,
+                                        Colours::lightgrey,
+                                        DocumentWindow::allButtons)
+        {
+            setUsingNativeTitleBar (true);
+            setContentOwned (new SpectrogramComponent(), true);
+            setResizable (true, true);
+            centreWithSize (getWidth(), getHeight());
+            setVisible (true);
+        }
+
+        void closeButtonPressed() override
+        {
+            // This is called when the user tries to close this window. Here, we'll just
+            // ask the app to quit when this happens, but you can change this to do
+            // whatever you need.
+            JUCEApplication::getInstance()->systemRequestedQuit();
+        }
+
+    private:
+        JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MainWindow)
+    };
+
+private:
+    ScopedPointer<MainWindow> mainWindow;
+};
+
+//==============================================================================
+// This macro generates the main() routine that launches the app.
+START_JUCE_APPLICATION (SimpleFFTExampleApplication)

examples/SimpleFFTExample/Source/SpectrogramComponent.h

@@ -0,0 +1,132 @@
+/*
+  ==============================================================================
+
+    JUCE demo code - use at your own risk!
+
+  ==============================================================================
+*/
+
+
+class SpectrogramComponent   : public AudioAppComponent,
+                               private Timer
+{
+public:
+    SpectrogramComponent()
+        : forwardFFT (fftOrder, false),
+          spectrogramImage (Image::RGB, 512, 512, true),
+          fifoIndex (0),
+          nextFFTBlockReady (false)
+    {
+        setOpaque (true);
+        setAudioChannels (2, 0);  // we want a couple of input channels but no outputs
+        startTimerHz (60);
+        setSize (700, 500);
+    }
+
+    ~SpectrogramComponent()
+    {
+        shutdownAudio();
+    }
+
+    //=======================================================================
+    void prepareToPlay (int /*samplesPerBlockExpected*/, double /*newSampleRate*/) override
+    {
+        // (nothing to do here)
+    }
+
+    void releaseResources() override
+    {
+        // (nothing to do here)
+    }
+
+    void getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill) override
+    {
+        if (bufferToFill.buffer->getNumChannels() > 0)
+        {
+            const float* channelData = bufferToFill.buffer->getWritePointer (0, bufferToFill.startSample);
+
+            for (int i = 0; i < bufferToFill.numSamples; ++i)
+                pushNextSampleIntoFifo (channelData[i]);
+        }
+    }
+
+    //=======================================================================
+    void paint (Graphics& g) override
+    {
+        g.fillAll (Colours::black);
+
+        g.setOpacity (1.0f);
+        g.drawImageWithin (spectrogramImage, 0, 0, getWidth(), getHeight(), RectanglePlacement::stretchToFit);
+    }
+
+    void timerCallback() override
+    {
+        if (nextFFTBlockReady)
+        {
+            drawNextLineOfSpectrogram();
+            nextFFTBlockReady = false;
+            repaint();
+        }
+    }
+
+    void pushNextSampleIntoFifo (float sample) noexcept
+    {
+        // if the fifo contains enough data, set a flag to say
+        // that the next line should now be rendered..
+        if (fifoIndex == fftSize)
+        {
+            if (! nextFFTBlockReady)
+            {
+                zeromem (fftData, sizeof (fftData));
+                memcpy (fftData, fifo, sizeof (fifo));
+                nextFFTBlockReady = true;
+            }
+
+            fifoIndex = 0;
+        }
+
+        fifo[fifoIndex++] = sample;
+    }
+
+    void drawNextLineOfSpectrogram()
+    {
+        const int rightHandEdge = spectrogramImage.getWidth() - 1;
+        const int imageHeight = spectrogramImage.getHeight();
+
+        // first, shuffle our image leftwards by 1 pixel..
+        spectrogramImage.moveImageSection (0, 0, 1, 0, rightHandEdge, imageHeight);
+
+        // then render our FFT data..
+        forwardFFT.performFrequencyOnlyForwardTransform (fftData);
+
+        // find the range of values produced, so we can scale our rendering to
+        // show up the detail clearly
+        Range<float> maxLevel = FloatVectorOperations::findMinAndMax (fftData, fftSize / 2);
+
+        for (int y = 0; y < imageHeight; ++y)
+        {
+            const float skewedProportionY = 1.0f - std::exp (std::log (y / (float) imageHeight) * 0.2f);
+            const int fftDataIndex = jlimit (0, fftSize / 2, (int) (skewedProportionY * fftSize / 2));
+            const float level = jmap (fftData[fftDataIndex], 0.0f, maxLevel.getEnd(), 0.0f, 1.0f);
+
+            spectrogramImage.setPixelAt (rightHandEdge, y, Colour::fromHSV (level, 1.0f, level, 1.0f));
+        }
+    }
+
+    enum
+    {
+        fftOrder = 10,
+        fftSize  = 1 << fftOrder
+    };
+
+private:
+    FFT forwardFFT;
+    Image spectrogramImage;
+
+    float fifo [fftSize];
+    float fftData [2 * fftSize];
+    int fifoIndex;
+    bool nextFFTBlockReady;
+
+    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (SpectrogramComponent)
+};