juce_StateVariableTPTFilter.h

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 /*
  ==============================================================================
 
   This file is part of the JUCE library.
   Copyright (c) 2022 - Raw Material Software Limited
 
   JUCE is an open source library subject to commercial or open-source
   licensing.
 
   By using JUCE, you agree to the terms of both the JUCE 7 End-User License
   Agreement and JUCE Privacy Policy.
 
   End User License Agreement: www.juce.com/juce-7-licence
   Privacy Policy: www.juce.com/juce-privacy-policy
 
   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).
 
   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.
 
  ==============================================================================
*/
 
namespace juce::dsp
{
 
enum class StateVariableTPTFilterType
{
    lowpass,
    bandpass,
    highpass
};
 
//==============================================================================
template <typename SampleType>
class StateVariableTPTFilter
{
public:
    //==============================================================================
    using Type = StateVariableTPTFilterType;
 
    //==============================================================================
    StateVariableTPTFilter();
 
    //==============================================================================
    void setType (Type newType);
 
    void setCutoffFrequency (SampleType newFrequencyHz);
 
    void setResonance (SampleType newResonance);
 
    //==============================================================================
    Type getType() const noexcept                      { return filterType; }
 
    SampleType getCutoffFrequency() const noexcept     { return cutoffFrequency; }
 
    SampleType getResonance() const noexcept           { return resonance; }
 
    //==============================================================================
    void prepare (const ProcessSpec& spec);
 
    void reset();
 
    void reset (SampleType newValue);
 
    void snapToZero() noexcept;
 
    //==============================================================================
    template <typename ProcessContext>
    void process (const ProcessContext& context) noexcept
    {
        const auto& inputBlock = context.getInputBlock();
        auto& outputBlock      = context.getOutputBlock();
        const auto numChannels = outputBlock.getNumChannels();
        const auto numSamples  = outputBlock.getNumSamples();
 
        jassert (inputBlock.getNumChannels() <= s1.size());
        jassert (inputBlock.getNumChannels() == numChannels);
        jassert (inputBlock.getNumSamples()  == numSamples);
 
        if (context.isBypassed)
        {
            outputBlock.copyFrom (inputBlock);
            return;
        }
 
        for (size_t channel = 0; channel < numChannels; ++channel)
        {
            auto* inputSamples  = inputBlock .getChannelPointer (channel);
            auto* outputSamples = outputBlock.getChannelPointer (channel);
 
            for (size_t i = 0; i < numSamples; ++i)
                outputSamples[i] = processSample ((int) channel, inputSamples[i]);
        }
 
       #if JUCE_DSP_ENABLE_SNAP_TO_ZERO
        snapToZero();
       #endif
    }
 
    //==============================================================================
    SampleType processSample (int channel, SampleType inputValue);
 
private:
    //==============================================================================
    void update();
 
    //==============================================================================
    SampleType g, h, R2;
    std::vector<SampleType> s1 { 2 }, s2 { 2 };
 
    double sampleRate = 44100.0;
    Type filterType = Type::lowpass;
    SampleType cutoffFrequency = static_cast<SampleType> (1000.0),
               resonance       = static_cast<SampleType> (1.0 / std::sqrt (2.0));
};
 
} // namespace juce::dsp