Add interface for interpolator selection

include/AudioInterpolator.h

@@ -0,0 +1,68 @@
+/*
+ * AudioInterpolator.h
+ *
+ * Copyright (c) 2024 saker
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef LMMS_AUDIO_INTERPOLATOR_H
+#define LMMS_AUDIO_INTERPOLATOR_H
+
+#include <functional>
+#include <variant>
+
+namespace lmms {
+class AudioInterpolator
+{
+public:
+	using FourPointInterpolator = std::function<float(float, float, float, float, float)>;
+	using TwoPointInterpolator = std::function<float(float, float, float)>;
+
+	constexpr static auto DefaultInterpolator = "hermite";
+
+	struct Interpolator
+	{
+		const char* name;
+		const char* displayName;
+		std::variant<FourPointInterpolator, TwoPointInterpolator> fn;
+	};
+
+	static auto interpolate(const float* buffer, size_t size, size_t index, float fracPosition) -> float;
+	static auto interpolators() -> const std::vector<Interpolator>&;
+
+	static void setPlaybackInterpolator(const char* name);
+	static void setExportInterpolator(const char* name);
+	static void setExporting(bool exporting);
+
+private:
+	static auto interpolate(FourPointInterpolator interpolator, const float* buffer, size_t size, size_t index,
+		float fracPosition) -> float;
+	static auto interpolate(
+		TwoPointInterpolator interpolator, const float* buffer, size_t size, size_t index, float fracPosition) -> float;
+	static auto findInterpolator(const char* name) -> Interpolator*;
+
+	static Interpolator* s_playbackInterpolator;
+	static Interpolator* s_exportInterpolator;
+	static bool s_exporting;
+	static std::vector<Interpolator> s_interpolators;
+};
+} // namespace lmms
+
+#endif // LMMS_AUDIO_INTERPOLATOR_H

src/core/audio/AudioInterpolator.cpp

@@ -0,0 +1,130 @@
+/*
+ * AudioInterpolator.cpp
+ *
+ * Copyright (c) 2024 saker
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include "AudioInterpolator.h"
+
+#include <cstring>
+
+#include "interpolation.h"
+#include "lmms_basics.h"
+
+namespace lmms {
+
+std::vector<AudioInterpolator::Interpolator> AudioInterpolator::s_interpolators
+	= {{"hermite", "4-point Hermite", hermiteInterpolate}, {"linear", "Linear", linearInterpolate}};
+
+AudioInterpolator::Interpolator* AudioInterpolator::s_playbackInterpolator
+	= AudioInterpolator::findInterpolator(DefaultInterpolator);
+AudioInterpolator::Interpolator* AudioInterpolator::s_exportInterpolator
+	= AudioInterpolator::findInterpolator(DefaultInterpolator);
+
+bool AudioInterpolator::s_exporting = false;
+
+float AudioInterpolator::interpolate(const float* buffer, size_t size, size_t index, float fracPosition)
+{
+	assert(s_playbackInterpolator && s_exportInterpolator
+		&& "Either the playback interpolator or export interpolator were not found");
+
+	const auto playbackFourPointInterpolator = std::get_if<FourPointInterpolator>(&s_playbackInterpolator->fn);
+	const auto playbackTwoPointInterpolator = std::get_if<TwoPointInterpolator>(&s_playbackInterpolator->fn);
+	const auto exportFourPointInterpolator = std::get_if<FourPointInterpolator>(&s_exportInterpolator->fn);
+	const auto exportTwoPointInterpolator = std::get_if<TwoPointInterpolator>(&s_exportInterpolator->fn);
+
+	if (s_exporting)
+	{
+		assert(s_exportInterpolator);
+		if (exportFourPointInterpolator)
+		{
+			return interpolate(*exportFourPointInterpolator, buffer, size, index, fracPosition);
+		}
+		else if (exportTwoPointInterpolator)
+		{
+			return interpolate(*exportTwoPointInterpolator, buffer, size, index, fracPosition);
+		}
+	}
+	else
+	{
+		assert(s_playbackInterpolator);
+		if (playbackFourPointInterpolator)
+		{
+			return interpolate(*playbackFourPointInterpolator, buffer, size, index, fracPosition);
+		}
+		else if (playbackTwoPointInterpolator)
+		{
+			return interpolate(*playbackTwoPointInterpolator, buffer, size, index, fracPosition);
+		}
+	}
+
+	return 0;
+}
+
+float AudioInterpolator::interpolate(
+	FourPointInterpolator interpolator, const float* buffer, size_t size, size_t index, float fracPosition)
+{
+	const auto x0 = index == 0 ? 0.0f : buffer[index - 1];
+	const auto x1 = buffer[index];
+	const auto x2 = (index + 1 * DEFAULT_CHANNELS) >= size ? 0.0f : buffer[index + 1 * DEFAULT_CHANNELS];
+	const auto x3 = (index + 2 * DEFAULT_CHANNELS) >= size ? 0.0f : buffer[index + 2 * DEFAULT_CHANNELS];
+	return interpolator(x0, x1, x2, x3, fracPosition);
+}
+
+float AudioInterpolator::interpolate(
+	TwoPointInterpolator interpolator, const float* buffer, size_t size, size_t index, float fracPosition)
+{
+	const auto x0 = buffer[index];
+	const auto x1 = (index + DEFAULT_CHANNELS) >= size ? 0.0f : buffer[index + DEFAULT_CHANNELS];
+	return interpolator(x0, x1, fracPosition);
+}
+
+void AudioInterpolator::setPlaybackInterpolator(const char* name)
+{
+	s_playbackInterpolator = findInterpolator(name);
+}
+
+void AudioInterpolator::setExportInterpolator(const char* name)
+{
+	s_exportInterpolator = findInterpolator(name);
+}
+
+void AudioInterpolator::setExporting(bool exporting)
+{
+	s_exporting = exporting;
+}
+
+auto AudioInterpolator::findInterpolator(const char* name) -> Interpolator*
+{
+	for (auto& interpolator : s_interpolators)
+	{
+		if (std::strcmp(interpolator.name, name)) { return &interpolator; }
+	}
+
+	return nullptr;
+}
+
+auto AudioInterpolator::interpolators() -> const std::vector<Interpolator>&
+{
+	return s_interpolators;
+}
+
+} // namespace lmms