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Source/Sampler/Effects/Distortion.h

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+/*
+  ==============================================================================
+
+    Distortion.h
+    Created: 30 Dec 2023 8:39:04pm
+    Author:  binya
+
+  ==============================================================================
+*/
+
+#pragma once
+#include <JuceHeader.h>
+
+#include "Effect.h"
+#include <gin_distortion.h>
+
+/** This is a simple Distortion class that wraps around gin::AirWindowsDistortion */
+class Distortion final : public Effect
+{
+public:
+    void initialize(int numChannels, int fxSampleRate) override
+    {
+        int numEffects = numChannels / 2 + numChannels % 2;
+        channelDistortions.resize(numEffects);
+        for (int ch = 0; ch < numEffects; ch++)
+        {
+            channelDistortions[ch] = std::make_unique<gin::AirWindowsDistortion>();
+            channelDistortions[ch]->setSampleRate(fxSampleRate);
+        }
+    }
+
+    void updateParams(float density, float highpass, float mix)
+    {
+        float mappedDensity = density >= 0.f ? juce::jmap<float>(density, 0.2f, 1.f) : juce::jmap<float>(density, -0.5f, 0.f, 0.f, 0.2f);
+
+        // We try to keep the gain of the distortion constant:
+        // This is a sigmoid function found manually from graphing the output of the distortion. When the mapped density < 0.2f, 
+        // a different function needs to be used, since the distortion actually behaves differently according to that threshold.
+        // Note that the gain parameter only applies if it's less than 1.f, so we need to increase the gain ourselves after processing.
+        float gainChange = mappedDensity >= 0.2f ? (0.2f * (1.f + expf(-7.f * (mappedDensity - 0.5f)))) : 1.f; 
+        postGain = mappedDensity < 0.2f ? 1.f / (4.f * mappedDensity + 0.2f) : 1.f;
+
+        for (const auto& channelDistortion : channelDistortions)
+            channelDistortion->setParams(mappedDensity, highpass, gainChange, mix);
+    }
+
+    void updateParams(const SamplerParameters& sampleSound, bool) override
+    {
+        updateParams(
+            sampleSound.distortionDensity->get(), 
+            sampleSound.distortionHighpass->get(), 
+            sampleSound.distortionMix->get()
+        );
+    }
+
+    void process(juce::AudioBuffer<float>& buffer, int numSamples, int startSample=0) override
+    {
+        bool lastIsMono = buffer.getNumChannels() % 2 == 1;
+        for (int ch = 0; ch < buffer.getNumChannels(); ch += 2)
+        {
+            // Note that I modified the gin header to make this more straightforward
+            if (lastIsMono && ch == buffer.getNumChannels() - 1)
+                channelDistortions[ch / 2]->process(buffer.getWritePointer(ch, startSample), buffer.getWritePointer(ch, startSample), numSamples);
+            else
+                channelDistortions[ch / 2]->process(buffer.getWritePointer(ch, startSample), buffer.getWritePointer(ch + 1, startSample), numSamples);
+        }
+        buffer.applyGain(startSample, numSamples, postGain);
+    }
+
+private:
+    std::vector<std::unique_ptr<gin::AirWindowsDistortion>> channelDistortions;
+    float postGain{ 0. };
+};