minor filter performance optimization

this only saves 0.1% CPU but this is probably the way i "should" do it

Author: tesselode

source/Filter.cpp

@@ -45,22 +45,50 @@ double StateVariableFilter::Process(double dt, double input, double cutoff, bool
 	return highPass ? high : low;
 }
 
+void MultiFilter::SetMode(FilterModes m)
+{
+	if (currentMode != m)
+	{
+		previousMode = currentMode;
+		currentMode = m;
+		crossfading = true;
+		currentModeMix = 0.0;
+	}
+}
+
 void MultiFilter::Process(double dt, double & l, double & r, double cutoff, bool highPass)
 {
-	for (int i = 0; i < std::size(mix); i++)
-		mix[i] += ((mode == i ? 1.0 : 0.0) - mix[i]) * 100.0 * dt;
+	switch (crossfading)
+	{
+	case true:
+	{
+		currentModeMix += 100.0 * dt;
+		if (currentModeMix >= 1.0)
+		{
+			auto current = currentMode;
+			currentModeMix = 1.0;
+			crossfading = false;
+			filters[previousMode]->Reset();
+		}
 
-	auto inL = l;
-	auto inR = r;
-	auto tempOutL = 0.0;
-	auto tempOutR = 0.0;
-	l = 0.0;
-	r = 0.0;
+		auto inL = l;
+		auto inR = r;
+		auto tempOutL = 0.0;
+		auto tempOutR = 0.0;
+		l = 0.0;
+		r = 0.0;
 
-	for (int i = 0; i < std::size(filters); i++)
-	{
-		filters[i]->Process(dt, inL, inR, cutoff, tempOutL, tempOutR, highPass);
-		l += tempOutL * mix[i];
-		r += tempOutR * mix[i];
+		filters[previousMode]->Process(dt, inL, inR, cutoff, tempOutL, tempOutR, highPass);
+		l += tempOutL * (1.0 - currentModeMix);
+		r += tempOutR * (1.0 - currentModeMix);
+		filters[currentMode]->Process(dt, inL, inR, cutoff, tempOutL, tempOutR, highPass);
+		l += tempOutL * currentModeMix;
+		r += tempOutR * currentModeMix;
+
+		break;
+	}
+	case false:
+		filters[currentMode]->Process(dt, l, r, cutoff, l, r, highPass);
+		break;
 	}
 }

source/Filter.h

@@ -9,12 +9,17 @@ enum FilterModes
 	twoPole,
 	fourPole,
 	stateVariable,
-	numFilterModes
+	numFilterModes,
+	noFilter
 };
 
 class OnePoleFilter
 {
 public:
+	void Reset()
+	{
+		a = 0.0;
+	}
 	double Process(double dt, double input, double cutoff, bool highPass = false);
 
 private:
@@ -24,6 +29,11 @@ class OnePoleFilter
 class TwoPoleFilter
 {
 public:
+	void Reset()
+	{
+		a = 0.0;
+		b = 0.0;
+	}
 	double Process(double dt, double input, double cutoff, bool highPass = false);
 
 private:
@@ -34,6 +44,13 @@ class TwoPoleFilter
 class FourPoleFilter
 {
 public:
+	void Reset()
+	{
+		a = 0.0;
+		b = 0.0;
+		c = 0.0;
+		d = 0.0;
+	}
 	double Process(double dt, double input, double cutoff, bool highPass = false);
 
 private:
@@ -46,6 +63,11 @@ class FourPoleFilter
 class StateVariableFilter
 {
 public:
+	void Reset()
+	{
+		band = 0.0;
+		low = 0.0;
+	}
 	double Process(double dt, double input, double cutoff, bool highPass = false);
 
 private:
@@ -57,13 +79,19 @@ class StateVariableFilter
 class DualFilterBase
 {
 public:
+	virtual void Reset() {}
 	virtual void Process(double dt, double inL, double inR, double cutoff, double &outL, double &outR, bool highPass = false) {}
 };
 
 template<class T>
 class DualFilter : public DualFilterBase
 {
 public:
+	void Reset()
+	{
+		left.Reset();
+		right.Reset();
+	}
 	void Process(double dt, double inL, double inR, double cutoff, double &outL, double &outR, bool highPass = false)
 	{
 		outL = left.Process(dt, inL, cutoff, highPass);
@@ -78,16 +106,18 @@ class DualFilter : public DualFilterBase
 class MultiFilter
 {
 public:
-	void SetMode(FilterModes m) { mode = m; }
+	void SetMode(FilterModes m);
 	void Process(double dt, double &l, double &r, double cutoff, bool highPass = false);
 
 private:
-	FilterModes mode = FilterModes::onePole;
 	std::array<std::unique_ptr<DualFilterBase>, numFilterModes> filters = {
 		std::unique_ptr<DualFilterBase>(new DualFilter<OnePoleFilter>()),
 		std::unique_ptr<DualFilterBase>(new DualFilter<TwoPoleFilter>()),
 		std::unique_ptr<DualFilterBase>(new DualFilter<FourPoleFilter>()),
 		std::unique_ptr<DualFilterBase>(new DualFilter<StateVariableFilter>())
 	};
-	std::array<double, numFilterModes> mix = {0.0, 0.0, 0.0, 0.0};
+	FilterModes currentMode = FilterModes::onePole;
+	FilterModes previousMode = FilterModes::noFilter;
+	bool crossfading = false;
+	double currentModeMix = 1.0;
 };