简单的问题-如何从单独的“结构”中的“类”访问变量？

Question

I am new to C++/JUCE. I have been working to get a basic synth running and just testing some things out to learn the ropes.

It's working fine already. But I'm still just learning my way around C++/JUCE and how to declare or access classes/objects/variables.

I'm trying to make a modification to something that I'm stuck with.

I have the following (just excerpts to demonstrate)…

This is where the synthesizer level is set:

struct SineWaveVoice   : public SynthesiserVoice
{
SineWaveVoice() {}

bool canPlaySound (SynthesiserSound* sound) override
{
    return dynamic_cast<SineWaveSound*> (sound) != nullptr;
}

void startNote (int midiNoteNumber, float velocity,
                SynthesiserSound*, int /*currentPitchWheelPosition*/) override
{
    currentAngle = 0.0;
    level = velocity * 0.15;
    tailOff = 0.0;

Ie. Level is set by velocity * 0.15.

In my test set up, I already have a level knob defined under MainContentComponent like this:

class MainContentComponent :    public AudioAppComponent,
                                private Timer

{
public:
    MainContentComponent()
        : synthAudioSource(keyboardState),
        keyboardComponent(keyboardState, MidiKeyboardComponent::horizontalKeyboard)

    {
        LabeledSlider* control = new LabeledSlider("Frequency");
        control->slider.setRange(20.0, 20000.0);
        control->slider.setSkewFactorFromMidPoint(500.0);
        control->slider.setNumDecimalPlacesToDisplay(1);
        control->slider.setValue(currentFrequency, dontSendNotification);
        control->slider.onValueChange = [this] { targetFrequency = frequency.slider.getValue(); };
        control->slider.setTextBoxStyle(Slider::TextBoxBelow, false, 100, 20);
        control->slider.setRange(50.0, 5000.0);
        control->slider.setSkewFactorFromMidPoint(500.0);
        control->slider.setNumDecimalPlacesToDisplay(1);
        addAndMakeVisible(knobs.add(control));

        control = new LabeledSlider("Level");
        control->slider.setRange(0.0, 1.0);
        control->slider.onValueChange = [this] { targetLevel = (float)level.slider.getValue(); };
        addAndMakeVisible(knobs.add(control));

....
private:
{

float currentLevel = 0.1f, targetLevel = 0.1f;
    LabeledSlider level{ "Level" };

So let's say I want to use this level slider variable “targetLevel” to be multiplied by the velocity in the “struct” above instead of 0.15.

What do I need to type up there to be able to access and use “targetLevel”? I tried multiple things but I can't quite figure it out.

Thanks

Answer 1

I am assuming that your SineWaveVoice lies within your SynthAudioSource class and that the voice is a part of a Synthesizer object. To access anything within your SineWaveVoice struct from MainContentComponent you need to expose this somehow via the SynthAudioSource. So my suggestion is that in your SynthAudioSource add a method like this:

void setLevel(double lvl)
{
    for (auto i=0; i<synth.getNumVoices(); i++)
    {
        SineWaveVoice *v = dynamic_cast<SineWaveVoice *>(synth.getVoice(i));
        v->level = lvl * v->velocity;
    }
}

Then to access this in your MainContentComponent you just do this:

control->slider.onValueChange = [this] {
    targetLevel = (float)level.slider.getValue();
    synthAudioSource.setLevel(targetLevel);
};

However, notice that this value will be overwritten every time you get a new startNote event. So you should probably store a copy of target level in your SineWaveVoice and multiply with that rather than 0.15.