JUCE/examples/PlugInSamples/InterAppAudioEffect/Source/SimpleMeter.h

#ifndef SIMPLEMETER_H_INCLUDED
#define SIMPLEMETER_H_INCLUDED

#include "../JuceLibraryCode/JuceHeader.h"

// A very simple decaying meter.
class SimpleMeter  : public Component,
                     private Timer
{
public:
    SimpleMeter()
    {
        startTimerHz (30);
    }

    //==============================================================================
    void paint (Graphics& g) override
    {
        g.fillAll(Colours::transparentBlack);

        auto area = g.getClipBounds();
        g.setColour (Colours::skyblue);
        g.fillRoundedRectangle(area.toFloat(), 6.0);

        auto unfilledHeight = area.getHeight() * (1.0 - level);
        g.reduceClipRegion (area.getX(), area.getY(),
                            area.getWidth(), (int) unfilledHeight);
        g.setColour (Colours::grey);
        g.fillRoundedRectangle(area.toFloat(), 6.0);
    }

    void resized() override {}

    //==============================================================================
    // Called from the audio thread.
    void update (float newLevel)
    {
        // We don't care if maxLevel gets set to zero (in timerCallback) between the
        // load and the assignment.
        maxLevel = jmax (maxLevel.load(), newLevel);
    }

private:
    //==============================================================================
    void timerCallback() override
    {
        auto callbackLevel = maxLevel.exchange (0.0);

        auto decayFactor = 0.95;
        if (callbackLevel > level)
            level = callbackLevel;
        else if (level > 0.001)
            level *= decayFactor;
        else
            level = 0;

        repaint();
    }

    std::atomic<float> maxLevel {0.0};
    float level = 0;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (SimpleMeter)
};

#if JUCE_PROJUCER_LIVE_BUILD

// Animate the meter in the Projucer live build.
struct MockSimpleMeter  : public Component,
                          private Timer
{
    MockSimpleMeter()
    {
        addAndMakeVisible (meter);
        resized();
        startTimerHz (100);
    }

    void paint (Graphics&) override {}

    void resized() override
    {
        meter.setBounds (getBounds());
    }

    void timerCallback() override
    {
        meter.update (std::pow (randomNumberGenerator.nextFloat(), 2));
    }

    SimpleMeter meter;
    Random randomNumberGenerator;
};

#endif

#endif  // SIMPLEMETER_H_INCLUDED