fixes #6354: Sample and Hold for LFO Controller (#6850)

* fixes #6354: Sample and Hold for LFO Controller

LFO controller's "white noise" wave shape didn't respect the frequency knob at all, so
Sample-and-Hold was added to extend the functionality of the LFO Controller with this
random waveshape. The original functionallity can still be accessed by setting the
FREQ knob to minimum (0.01)

---------

Co-authored-by: Kevin Zander <veratil@gmail.com>
Co-authored-by: saker <sakertooth@gmail.com>

include/DataFile.h

@@ -126,6 +126,7 @@ private:
 	void upgrade_defaultTripleOscillatorHQ();
 	void upgrade_mixerRename();
 	void upgrade_bbTcoRename();
+	void upgrade_sampleAndHold();
 
 	// List of all upgrade methods
 	static const std::vector<UpgradeMethod> UPGRADE_METHODS;

include/LfoController.h

@@ -86,6 +86,7 @@ protected:
 	sample_t (*m_sampleFunction)( const float );
 
 private:
+	float m_heldSample;
 	SampleBuffer * m_userDefSampleBuffer;
 
 protected slots:

src/core/DataFile.cpp

@@ -79,6 +79,7 @@ const std::vector<DataFile::UpgradeMethod> DataFile::UPGRADE_METHODS = {
 	&DataFile::upgrade_automationNodes  ,   &DataFile::upgrade_extendedNoteRange,
 	&DataFile::upgrade_defaultTripleOscillatorHQ,
 	&DataFile::upgrade_mixerRename      ,   &DataFile::upgrade_bbTcoRename,
+	&DataFile::upgrade_sampleAndHold    ,
 };
 
 // Vector of all versions that have upgrade routines.
@@ -1762,6 +1763,23 @@ void DataFile::upgrade_bbTcoRename()
 }
 
 
+// Set LFO speed to 0.01 on projects made before sample-and-hold PR
+void DataFile::upgrade_sampleAndHold()
+{
+	QDomNodeList elements = elementsByTagName("lfocontroller");
+	for (int i = 0; i < elements.length(); ++i)
+	{
+		if (elements.item(i).isNull()) { continue; }
+		auto e = elements.item(i).toElement();
+		// Correct old random wave LFO speeds
+		if (e.attribute("wave").toInt() == 6)
+		{
+			e.setAttribute("speed",0.01f);
+		}
+	}
+}
+
+
 void DataFile::upgrade()
 {
 	// Runs all necessary upgrade methods

src/core/LfoController.cpp

@@ -88,6 +88,7 @@ void LfoController::updateValueBuffer()
 {
 	m_phaseOffset = m_phaseModel.value() / 360.0;
 	float phase = m_currentPhase + m_phaseOffset;
+	float phasePrev = 0.0f;
 
 	// roll phase up until we're in sync with period counter
 	m_bufferLastUpdated++;
@@ -102,20 +103,45 @@ void LfoController::updateValueBuffer()
 	ValueBuffer *amountBuffer = m_amountModel.valueBuffer();
 	int amountInc = amountBuffer ? 1 : 0;
 	float *amountPtr = amountBuffer ? &(amountBuffer->values()[ 0 ] ) : &amount;
+	Oscillator::WaveShape waveshape = static_cast<Oscillator::WaveShape>(m_waveModel.value());
 
 	for( float& f : m_valueBuffer )
 	{
-		const float currentSample = m_sampleFunction != nullptr
-			? m_sampleFunction( phase )
-			: m_userDefSampleBuffer->userWaveSample( phase );
+		float currentSample = 0;
+		switch (waveshape)
+		{
+		case Oscillator::WaveShape::WhiteNoise:
+		{
+			if (absFraction(phase) < absFraction(phasePrev))
+			{
+				// Resample when phase period has completed
+				m_heldSample = m_sampleFunction(phase);
+			}
+			currentSample = m_heldSample;
+			break;
+		}
+		case Oscillator::WaveShape::UserDefined:
+		{
+			currentSample = m_userDefSampleBuffer->userWaveSample(phase);
+			break;
+		}
+		default:
+		{
+			if (m_sampleFunction != nullptr)
+			{
+				currentSample = m_sampleFunction(phase);
+			}
+		}
+	}
 
 		f = std::clamp(m_baseModel.value() + (*amountPtr * currentSample / 2.0f), 0.0f, 1.0f);
 
+		phasePrev = phase;
 		phase += 1.0 / m_duration;
 		amountPtr += amountInc;
 	}
 
-	m_currentPhase = absFraction( phase - m_phaseOffset );
+	m_currentPhase = absFraction(phase - m_phaseOffset);
 	m_bufferLastUpdated = s_periods;
 }