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externals/openal-soft/alc/effects/distortion.cpp

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+/**
+ * OpenAL cross platform audio library
+ * Copyright (C) 2013 by Mike Gorchak
+ * This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Library General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ *  License along with this library; if not, write to the
+ *  Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ * Or go to http://www.gnu.org/copyleft/lgpl.html
+ */
+
+#include "config.h"
+
+#include <algorithm>
+#include <array>
+#include <cstdlib>
+#include <iterator>
+
+#include "alc/effects/base.h"
+#include "almalloc.h"
+#include "alnumbers.h"
+#include "alnumeric.h"
+#include "alspan.h"
+#include "core/bufferline.h"
+#include "core/context.h"
+#include "core/devformat.h"
+#include "core/device.h"
+#include "core/effectslot.h"
+#include "core/filters/biquad.h"
+#include "core/mixer.h"
+#include "core/mixer/defs.h"
+#include "intrusive_ptr.h"
+
+
+namespace {
+
+struct DistortionState final : public EffectState {
+    /* Effect gains for each channel */
+    float mGain[MaxAmbiChannels]{};
+
+    /* Effect parameters */
+    BiquadFilter mLowpass;
+    BiquadFilter mBandpass;
+    float mAttenuation{};
+    float mEdgeCoeff{};
+
+    alignas(16) float mBuffer[2][BufferLineSize]{};
+
+
+    void deviceUpdate(const DeviceBase *device, const BufferStorage *buffer) override;
+    void update(const ContextBase *context, const EffectSlot *slot, const EffectProps *props,
+        const EffectTarget target) override;
+    void process(const size_t samplesToDo, const al::span<const FloatBufferLine> samplesIn,
+        const al::span<FloatBufferLine> samplesOut) override;
+
+    DEF_NEWDEL(DistortionState)
+};
+
+void DistortionState::deviceUpdate(const DeviceBase*, const BufferStorage*)
+{
+    mLowpass.clear();
+    mBandpass.clear();
+}
+
+void DistortionState::update(const ContextBase *context, const EffectSlot *slot,
+    const EffectProps *props, const EffectTarget target)
+{
+    const DeviceBase *device{context->mDevice};
+
+    /* Store waveshaper edge settings. */
+    const float edge{minf(std::sin(al::numbers::pi_v<float>*0.5f * props->Distortion.Edge),
+        0.99f)};
+    mEdgeCoeff = 2.0f * edge / (1.0f-edge);
+
+    float cutoff{props->Distortion.LowpassCutoff};
+    /* Bandwidth value is constant in octaves. */
+    float bandwidth{(cutoff / 2.0f) / (cutoff * 0.67f)};
+    /* Divide normalized frequency by the amount of oversampling done during
+     * processing.
+     */
+    auto frequency = static_cast<float>(device->Frequency);
+    mLowpass.setParamsFromBandwidth(BiquadType::LowPass, cutoff/frequency/4.0f, 1.0f, bandwidth);
+
+    cutoff = props->Distortion.EQCenter;
+    /* Convert bandwidth in Hz to octaves. */
+    bandwidth = props->Distortion.EQBandwidth / (cutoff * 0.67f);
+    mBandpass.setParamsFromBandwidth(BiquadType::BandPass, cutoff/frequency/4.0f, 1.0f, bandwidth);
+
+    static constexpr auto coeffs = CalcDirectionCoeffs({0.0f, 0.0f, -1.0f});
+
+    mOutTarget = target.Main->Buffer;
+    ComputePanGains(target.Main, coeffs.data(), slot->Gain*props->Distortion.Gain, mGain);
+}
+
+void DistortionState::process(const size_t samplesToDo, const al::span<const FloatBufferLine> samplesIn, const al::span<FloatBufferLine> samplesOut)
+{
+    const float fc{mEdgeCoeff};
+    for(size_t base{0u};base < samplesToDo;)
+    {
+        /* Perform 4x oversampling to avoid aliasing. Oversampling greatly
+         * improves distortion quality and allows to implement lowpass and
+         * bandpass filters using high frequencies, at which classic IIR
+         * filters became unstable.
+         */
+        size_t todo{minz(BufferLineSize, (samplesToDo-base) * 4)};
+
+        /* Fill oversample buffer using zero stuffing. Multiply the sample by
+         * the amount of oversampling to maintain the signal's power.
+         */
+        for(size_t i{0u};i < todo;i++)
+            mBuffer[0][i] = !(i&3) ? samplesIn[0][(i>>2)+base] * 4.0f : 0.0f;
+
+        /* First step, do lowpass filtering of original signal. Additionally
+         * perform buffer interpolation and lowpass cutoff for oversampling
+         * (which is fortunately first step of distortion). So combine three
+         * operations into the one.
+         */
+        mLowpass.process({mBuffer[0], todo}, mBuffer[1]);
+
+        /* Second step, do distortion using waveshaper function to emulate
+         * signal processing during tube overdriving. Three steps of
+         * waveshaping are intended to modify waveform without boost/clipping/
+         * attenuation process.
+         */
+        auto proc_sample = [fc](float smp) -> float
+        {
+            smp = (1.0f + fc) * smp/(1.0f + fc*std::abs(smp));
+            smp = (1.0f + fc) * smp/(1.0f + fc*std::abs(smp)) * -1.0f;
+            smp = (1.0f + fc) * smp/(1.0f + fc*std::abs(smp));
+            return smp;
+        };
+        std::transform(std::begin(mBuffer[1]), std::begin(mBuffer[1])+todo, std::begin(mBuffer[0]),
+            proc_sample);
+
+        /* Third step, do bandpass filtering of distorted signal. */
+        mBandpass.process({mBuffer[0], todo}, mBuffer[1]);
+
+        todo >>= 2;
+        const float *outgains{mGain};
+        for(FloatBufferLine &output : samplesOut)
+        {
+            /* Fourth step, final, do attenuation and perform decimation,
+             * storing only one sample out of four.
+             */
+            const float gain{*(outgains++)};
+            if(!(std::fabs(gain) > GainSilenceThreshold))
+                continue;
+
+            for(size_t i{0u};i < todo;i++)
+                output[base+i] += gain * mBuffer[1][i*4];
+        }
+
+        base += todo;
+    }
+}
+
+
+struct DistortionStateFactory final : public EffectStateFactory {
+    al::intrusive_ptr<EffectState> create() override
+    { return al::intrusive_ptr<EffectState>{new DistortionState{}}; }
+};
+
+} // namespace
+
+EffectStateFactory *DistortionStateFactory_getFactory()
+{
+    static DistortionStateFactory DistortionFactory{};
+    return &DistortionFactory;
+}