Add the width effect

src/CMakeLists.txt

@@ -27,6 +27,7 @@ set (SFIZZ_SOURCES
     sfizz/effects/Limiter.cpp
     sfizz/effects/Rectify.cpp
     sfizz/effects/Gain.cpp
+    sfizz/effects/Width.cpp
 )
 include (SfizzSIMDSourceFiles)
 

src/sfizz/Effects.cpp

@@ -17,6 +17,7 @@
 #include "effects/Limiter.h"
 #include "effects/Rectify.h"
 #include "effects/Gain.h"
+#include "effects/Width.h"
 #include <algorithm>
 
 namespace sfz {
@@ -33,6 +34,7 @@ void EffectFactory::registerStandardEffectTypes()
     // extensions (book)
     registerEffectType("rectify", fx::Rectify::makeInstance);
     registerEffectType("gain", fx::Gain::makeInstance);
+    registerEffectType("width", fx::Width::makeInstance);
 }
 
 void EffectFactory::registerEffectType(absl::string_view name, Effect::MakeInstance& make)

src/sfizz/effects/Width.cpp

@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+
+/**
+   Note(jpc): this effect is book-only, mentioned but not documented
+
+   Note(jpc): implementation status
+
+- [x] width
+- [ ] width_oncc
+ */
+
+#include "Width.h"
+#include "Opcode.h"
+#include "SIMDHelpers.h"
+#include "absl/memory/memory.h"
+
+namespace sfz {
+namespace fx {
+
+    void Width::setSampleRate(double sampleRate)
+    {
+        (void)sampleRate;
+    }
+
+    void Width::setSamplesPerBlock(int samplesPerBlock)
+    {
+        _tempBuffer.resize(samplesPerBlock);
+    }
+
+    void Width::clear()
+    {
+    }
+
+    void Width::process(const float* const inputs[], float* const outputs[], unsigned nframes)
+    {
+        const float baseWidth = _width;
+
+        absl::Span<float> widths = _tempBuffer.getSpan(0);
+        std::fill(widths.begin(), widths.end(), baseWidth);
+
+        absl::Span<const float> input1 { inputs[0], nframes };
+        absl::Span<const float> input2 { inputs[1], nframes };
+        absl::Span<float> output1 { outputs[0], nframes };
+        absl::Span<float> output2 { outputs[1], nframes };
+
+        for (unsigned i = 0; i < nframes; ++i) {
+            float l = input1[i];
+            float r = input2[i];
+
+            float w = clamp((widths[i] + 100.0f) * 0.005f, 0.0f, 1.0f);
+            float coeff1 = _internals::panLookup(w);
+            float coeff2 = _internals::panLookup(1.0f - w);
+
+            output1[i] = l * coeff2 + r * coeff1;
+            output2[i] = l * coeff1 + r * coeff2;
+        }
+    }
+
+    std::unique_ptr<Effect> Width::makeInstance(absl::Span<const Opcode> members)
+    {
+        auto fx = absl::make_unique<Width>();
+
+        for (const Opcode& opc : members) {
+            switch (opc.lettersOnlyHash) {
+            case hash("width"):
+                setValueFromOpcode(opc, fx->_width, {-100.0f, 100.0f});
+                break;
+            }
+        }
+
+        return CXX11_MOVE(fx);
+    }
+
+} // namespace fx
+} // namespace sfz

src/sfizz/effects/Width.h

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#pragma once
+#include "Effects.h"
+
+namespace sfz {
+namespace fx {
+
+    /**
+     * @brief Stereo width effect
+     */
+    class Width : public Effect {
+    public:
+        /**
+         * @brief Initializes with the given sample rate.
+         */
+        void setSampleRate(double sampleRate) override;
+
+        /**
+         * @brief Sets the maximum number of frames to render at a time. The actual
+         * value can be lower but should never be higher.
+         */
+        void setSamplesPerBlock(int samplesPerBlock) override;
+
+        /**
+         * @brief Reset the state to initial.
+         */
+        void clear() override;
+
+        /**
+         * @brief Copy the input signal to the output
+         */
+        void process(const float* const inputs[], float* const outputs[], unsigned nframes) override;
+
+        /**
+          * @brief Instantiates given the contents of the <effect> block.
+          */
+        static std::unique_ptr<Effect> makeInstance(absl::Span<const Opcode> members);
+
+    private:
+        float _width = 100;
+        AudioBuffer<float, 1> _tempBuffer { 1, config::defaultSamplesPerBlock };
+    };
+
+} // namespace fx
+} // namespace sfz