[JUCE API] Getting BPM From DAW

To implement tempo delay, you need to know the BPM.

Since the DAW already contains BPM information, you should use the JUCE API to retrieve it.

void EulerDelayAudioProcessor::updateBpm(double& outBpm) noexcept
{
    juce::AudioPlayHead* playhead = getPlayHead();
    if(playhead==nullptr)
    {
        return;
    }
    
    auto positioninfo =  playhead->getPosition();
    
    if(!positioninfo)
    {
        return;
    }
    
    auto bpmFromDAW = positioninfo->getBpm();
    if(bpmFromDAW)
    {
       outBpm = *bpmFromDAW;
    }
    
}

getPlayHead()

• This method, which belongs to the AudioProcessor class
• Serves as an entry point to obtain playback state and position information from the DAW.
• It returns an AudioPlayHead*, through which you can access timing details including the BPM.

AudioPlayHead::PositionInfo

• When you call playHead->getPosition(), you can obtain the current playback position and tempo (BPM) information through this structure.

getBpm()

• This function retrieves the BPM from the PositionInfo object.
• It returns a std::optional, meaning it only holds a valid value if BPM information is available.

std::optional ?

std::optional is a type that may or may not contain a value, and can be checked similarly to a pointer.
Since it holds an actual value inside, you can access it using *optional.
Because the return type can be complex, using auto makes the code simpler and more readable.