Sketching out some thoughts for an oF DSP chain

main.cpp

#include <vector>
#include <math.h>
#include <iostream>

using namespace std;

// some shortcuts to make this sketch simpler
typedef vector<float> ofSoundBuffer;
size_t bufferSize = 16;

#pragma mark Base Classes

// - - - - - - -
// Base class for everything in the DSP chain
class ofSoundNode {
protected:
	virtual bool setSource(ofSoundNode &source) {
		return false;
	}
	
	virtual void handleDisconnect(ofSoundNode &source) {
		destination = NULL;
	}
	
	ofSoundNode * destination;
	
public:
	ofSoundNode()
	: destination(NULL) { }
	
	virtual void renderIntoBuffer(ofSoundBuffer &outBuffer) {
		fill(outBuffer.begin(), outBuffer.end(), 0);
	}
	
	virtual bool connectTo(ofSoundNode &newDestination) {
		bool connectionSuccess = newDestination.setSource(*this);
		
		if(connectionSuccess) {
			if(destination) {
				destination->handleDisconnect(*this);
			}
			destination = &newDestination;
		}
		
		return connectionSuccess;
	}
}
ofGlobalSilentSoundNode; // <- Global instance which acts as a "no source" node / sentinel value

// - - - - - - -
// Shortcut subclass for a node which produces sound and has no source
class ofSoundGenerator : public ofSoundNode {
protected:
	virtual void produceSound(ofSoundBuffer &outBuffer) = 0;
	
public:
	void renderIntoBuffer(ofSoundBuffer &outBuffer) {
		produceSound(outBuffer);
	}
};

// - - - - - - -
// Shortcut subclass for a node which takes in sound, processes it, and sends it down the chain
class ofSoundEffect : public ofSoundNode {
protected:
	virtual void processSound(const ofSoundBuffer &inBuffer, ofSoundBuffer &outBuffer) = 0;
	
	bool setSource(ofSoundNode &source) {
		this->source = &source;
		return true;
	}
	
	ofSoundNode * source;
	
public:
	ofSoundEffect()
	: source(&ofGlobalSilentSoundNode) { }
	
	void renderIntoBuffer(ofSoundBuffer &outBuffer) {
		if(source) {
			source->renderIntoBuffer(outBuffer);
		}
		processSound(outBuffer, outBuffer);
	}
};

#pragma mark - Example Implementations

// - - - - - - -
// sine wave generator
class SineSynth : public ofSoundGenerator {
	double phase;
protected:
	void produceSound(ofSoundBuffer &outBuffer) {
		for(int i = 0; i < outBuffer.size(); i++) {
			outBuffer[i] = sin(phase);
			phase += 0.5;
		}
	}
};

// - - - - - - -
// "tremolo" effect (sets every other other sample to 0)
class Tremolo : public ofSoundEffect {
	long sampleCounter;
protected:
	void processSound(const ofSoundBuffer &inBuffer, ofSoundBuffer &outBuffer) {
		size_t bufferSize = min(inBuffer.size(), outBuffer.size());
		for(int i = 0; i < bufferSize; i++) {
			outBuffer[i] = (sampleCounter % 2) ? inBuffer[i] : 0;
			sampleCounter++;
		}
	}
};

// - - - - - - -
// "amplifier" effect (multiplies every sample by 0.5)
class Amplifier : public ofSoundEffect {
protected:
	void processSound(const ofSoundBuffer &inBuffer, ofSoundBuffer &outBuffer) {
		size_t bufferSize = min(inBuffer.size(), outBuffer.size());
		for(int i = 0; i < bufferSize; i++) {
			outBuffer[i] = inBuffer[i] * 0.5;
		}
	}
};

// - - - - - - -
// 8 channel simple additive mixer, handles its own connections
class Mixer : public ofSoundNode {
	ofSoundNode * sources[8];
	ofSoundBuffer buffers[8];
	
protected:
	bool setSource(ofSoundNode & source) {
		cout << "Mixer : use addSourceOnBus() instead of connectTo()" << endl;
		return false;
	}
	
	void handleDisconnect(ofSoundNode & source) {
		for(int i = 0; i < 8; i++) {
			if(sources[i] == &source) {
				sources[i] = NULL;
				return;
			}
		}
	}
	
public:
	Mixer() {
		for(int i = 0; i < 8; i++) {
			sources[i] = NULL;
			buffers[i] = ofSoundBuffer(bufferSize);
		}
	}
	
	void addSourceOnBus(ofSoundNode & source, unsigned bus) {
		source.connectTo(ofGlobalSilentSoundNode);
		sources[bus] = &source;
	}
	
	void renderIntoBuffer(ofSoundBuffer &outBuffer) {
		for(int i = 0; i < 8; i++) {
			if(sources[i]) {
				sources[i]->renderIntoBuffer(buffers[i]);
			}
		}
		
		for(int i = 0; i < bufferSize; i++) {
			float totalSample = 0;
			for(int j = 0; j < 8; j++) {
				totalSample += buffers[j][i];
			}
			outBuffer[i] = totalSample;
		}
	}
};

#pragma mark - Example Program

int main(int argc, const char * argv[]) {
	
	// [A] simple example
	// setting up a chain and rendering through it
	ofSoundBuffer bufferA(bufferSize);
	SineSynth     synth;
	Tremolo       tremolo;
	Amplifier     amp;
	
	// this sets up an audio path of synth -> tremolo -> amp
	synth.connectTo(tremolo);
	tremolo.connectTo(amp);
	
	// causes amp to pull from tremolo, and tremolo to pull from synth
	amp.renderIntoBuffer(bufferA);
	
	printf("[A] : ");
	for(int i = 0; i < bufferA.size(); i++) {
		printf("%+.1f ", bufferA[i]);
	}
	printf("\n");
	
	// [B] auto disconnect
	// connecting synth straight to amp, disconnecting from tremolo
	// in the process
	synth.connectTo(amp);
	ofSoundBuffer bufferB(bufferSize);
	amp.renderIntoBuffer(bufferB);
	
	printf("[B] : ");
	for(int i = 0; i < bufferB.size(); i++) {
		printf("%+.1f ", bufferB[i]);
	}
	printf("\n");
	
	// [C] mixer
	// demonstrating mixer using its own semantics for connections,
	// in order to make things less ambiguous
	Mixer mixer;
	amp.connectTo(mixer); // <- generates a warning message, doesn't do anything else
	mixer.addSourceOnBus(amp, 2); // <- actually makes the connection
	ofSoundBuffer bufferC(bufferSize);
	mixer.renderIntoBuffer(bufferC);
	
	printf("[C] : ");
	for(int i = 0; i < bufferC.size(); i++) {
		printf("%+.1f ", bufferC[i]);
	}
	
    return 0;
}

Output

[A] : +0.0 +0.2 +0.0 +0.5 +0.0 +0.3 +0.0 -0.2 +0.0 -0.5 +0.0 -0.4 +0.0 +0.1 +0.0 +0.5 
[B] : +0.5 +0.4 +0.2 -0.0 -0.3 -0.4 -0.5 -0.4 -0.3 -0.0 +0.2 +0.4 +0.5 +0.5 +0.3 +0.1 
Mixer : use addSourceOnBus() instead of connectTo()
[C] : -0.1 -0.4 -0.5 -0.5 -0.4 -0.2 +0.1 +0.3 +0.5 +0.5 +0.4 +0.2 -0.0 -0.2 -0.4 -0.5