Util: Start bringing up new resampler

include/mgba-util/audio-resampler.h

@@ -0,0 +1,37 @@
+/* Copyright (c) 2013-2024 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef M_AUDIO_RESAMPLER_H
+#define M_AUDIO_RESAMPLER_H
+
+#include <mgba-util/common.h>
+
+CXX_GUARD_START
+
+#include <mgba-util/interpolator.h>
+
+struct mAudioBuffer;
+struct mAudioResampler {
+	struct mAudioBuffer* source;
+	struct mAudioBuffer* destination;
+	double sourceRate;
+	double destRate;
+	double timestamp;
+	double lowWaterMark;
+	double highWaterMark;
+	struct mInterpolatorSinc interp;
+	bool consume;
+};
+
+void mAudioResamplerInit(struct mAudioResampler*);
+void mAudioResamplerDeinit(struct mAudioResampler*);
+void mAudioResamplerSetSource(struct mAudioResampler*, struct mAudioBuffer* source, double rate, bool consume);
+void mAudioResamplerSetDestination(struct mAudioResampler*, struct mAudioBuffer* destination, double rate);
+size_t mAudioResamplerProcess(struct mAudioResampler*);
+
+CXX_GUARD_END
+
+#endif
+

include/mgba-util/interpolator.h

@@ -8,12 +8,15 @@
 
 #include <mgba-util/common.h>
 
-struct mInterpData {
-	int16_t (*at)(const void* mInterpData, size_t index);
+CXX_GUARD_START
+
+struct mInterpolationData {
+	int16_t (*at)(int index, const void* context);
+	void* context;
 };
 
 struct mInterpolator {
-	int16_t (*interpolate)(const struct mInterpolator* interp, const struct mInterpData* data, double time, double sampleStep);
+	int16_t (*interpolate)(const struct mInterpolator* interp, const struct mInterpolationData* data, double time, double sampleStep);
 };
 
 struct mInterpolatorSinc {
@@ -28,4 +31,6 @@ struct mInterpolatorSinc {
 void mInterpolatorSincInit(struct mInterpolatorSinc* interp, unsigned resolution, unsigned width);
 void mInterpolatorSincDeinit(struct mInterpolatorSinc* interp);
 
+CXX_GUARD_END
+
 #endif

src/util/CMakeLists.txt

@@ -13,6 +13,8 @@ set(BASE_SOURCE_FILES
 
 set(SOURCE_FILES
 	${BASE_SOURCE_FILES}
+	audio-buffer.c
+	audio-resampler.c
 	convolve.c
 	elf-read.c
 	geometry.c

src/util/audio-buffer.c

@@ -9,7 +9,7 @@
 
 void mAudioBufferInit(struct mAudioBuffer* buffer, size_t capacity, unsigned channels) {
 	mCircleBufferInit(&buffer->data, capacity * channels * sizeof(int16_t));
-	buffer->channels = capacity;
+	buffer->channels = channels;
 }
 
 void mAudioBufferDeinit(struct mAudioBuffer* buffer) {

src/util/audio-resampler.c

@@ -0,0 +1,94 @@
+/* Copyright (c) 2013-2024 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#include <mgba-util/audio-resampler.h>
+
+#include <mgba-util/audio-buffer.h>
+
+#define MAX_CHANNELS 2
+
+struct mAudioResamplerData {
+	struct mAudioResampler* resampler;
+	unsigned channel;
+};
+
+static int16_t _sampleAt(int index, const void* context) {
+	const struct mAudioResamplerData* data = context;
+	if (index < 0) {
+		return 0;
+	}
+	return mAudioBufferPeek(data->resampler->source, data->channel, index);
+}
+
+void mAudioResamplerInit(struct mAudioResampler* resampler) {
+	memset(resampler, 0, sizeof(*resampler));
+	mInterpolatorSincInit(&resampler->interp, 0, 0);
+	resampler->lowWaterMark = resampler->interp.width;
+	resampler->highWaterMark = 0;
+}
+
+void mAudioResamplerDeinit(struct mAudioResampler* resampler) {
+	mInterpolatorSincDeinit(&resampler->interp);
+	resampler->source = NULL;
+	resampler->destination = NULL;
+}
+
+void mAudioResamplerSetSource(struct mAudioResampler* resampler, struct mAudioBuffer* source, double rate, bool consume) {
+	resampler->source = source;
+	resampler->sourceRate = rate;
+	resampler->consume = consume;
+}
+
+void mAudioResamplerSetDestination(struct mAudioResampler* resampler, struct mAudioBuffer* destination, double rate) {
+	resampler->destination = destination;
+	resampler->destRate = rate;	
+}
+
+size_t mAudioResamplerProcess(struct mAudioResampler* resampler) {
+	int16_t sampleBuffer[MAX_CHANNELS] = {0};
+	double timestep = resampler->sourceRate / resampler->destRate;
+	double timestamp = resampler->timestamp;
+	struct mInterpolator* interp = &resampler->interp.d;
+	struct mAudioResamplerData context = {
+		.resampler = resampler,
+	};
+	struct mInterpolationData data = {
+		.at = _sampleAt,
+		.context = &context,
+	};
+
+	size_t read = 0;
+	if (resampler->source->channels > MAX_CHANNELS) {
+		abort();
+	}
+
+	while (true) {
+		if (timestamp + resampler->highWaterMark >= mAudioBufferAvailable(resampler->source)) {
+			break;
+		}
+		if (mAudioBufferAvailable(resampler->destination) == mAudioBufferCapacity(resampler->destination)) {
+			break;
+		}
+
+		size_t channel;
+		for (channel = 0; channel < resampler->source->channels; ++channel) {
+			context.channel = channel;
+			sampleBuffer[channel] = interp->interpolate(interp, &data, timestamp, timestep);
+		}
+		if (!mAudioBufferWrite(resampler->destination, sampleBuffer, 1)) {
+			break;
+		}
+		timestamp += timestep;
+		++read;
+	}
+
+	if (resampler->consume && timestamp > resampler->lowWaterMark) {
+		size_t drop = timestamp - resampler->lowWaterMark;
+		drop = mAudioBufferRead(resampler->source, NULL, drop);
+		timestamp -= drop;
+	}
+	resampler->timestamp = timestamp;
+	return read;
+}

src/util/interpolator.c

@@ -10,7 +10,7 @@ enum {
 	mSINC_WIDTH = 8,
 };
 
-static int16_t mInterpolatorSincInterpolate(const struct mInterpolator*, const struct mInterpData*, double time, double sampleStep);
+static int16_t mInterpolatorSincInterpolate(const struct mInterpolator*, const struct mInterpolationData*, double time, double sampleStep);
 
 void mInterpolatorSincInit(struct mInterpolatorSinc* interp, unsigned resolution, unsigned width) {
 	interp->d.interpolate = mInterpolatorSincInterpolate;
@@ -33,6 +33,9 @@ void mInterpolatorSincInit(struct mInterpolatorSinc* interp, unsigned resolution
 	interp->sincLut[0] = 0;
 	interp->windowLut[0] = 1;
 
+	interp->width = width;
+	interp->resolution = resolution;
+
 	unsigned i;
 	for (i = 1; i <= samples; ++i, x += dx, y += dy) {
 		interp->sincLut[i] = x < width ? sin(x) / x : 0.0;
@@ -46,27 +49,27 @@ void mInterpolatorSincDeinit(struct mInterpolatorSinc* interp) {
 	free(interp->windowLut);
 }
 
-int16_t mInterpolatorSincInterpolate(const struct mInterpolator* interpolator, const struct mInterpData* data, double time, double sampleStep) {
+int16_t mInterpolatorSincInterpolate(const struct mInterpolator* interpolator, const struct mInterpolationData* data, double time, double sampleStep) {
 	struct mInterpolatorSinc* interp = (struct mInterpolatorSinc*) interpolator;
-	ssize_t index = (ssize_t) time;
+	int index = time;
 	double subsample = time - floor(time);
-	unsigned step = sampleStep > 1 ? interp->resolution * sampleStep : interp->resolution;
+	unsigned step = sampleStep < 1 ? interp->resolution * sampleStep : interp->resolution;
 	unsigned yShift = subsample * step;
 	unsigned xShift = subsample * interp->resolution;
 	double sum = 0.0;
 	double kernelSum = 0.0;
 	double kernel;
 
-	ssize_t i;
-	for (i = 1 - (ssize_t) interp->width; i <= (ssize_t) interp->width; ++i) {
-		unsigned window = i * interp->resolution;
+	int i;
+	for (i = 1 - (int) interp->width; i <= (int) interp->width; ++i) {
+		unsigned window = (i >= 0 ? i : -i) * interp->resolution;
 		if (yShift > window) {
 			window = yShift - window;
 		} else {
 			window -= yShift;
 		}
 
-		unsigned sinc = i * step;
+		unsigned sinc = (i >= 0 ? i : -i) * step;
 		if (xShift > sinc) {
 			sinc = xShift - sinc;
 		} else {
@@ -75,7 +78,7 @@ int16_t mInterpolatorSincInterpolate(const struct mInterpolator* interpolator, c
 
 		kernel = interp->sincLut[sinc] * interp->windowLut[window];
 		kernelSum += kernel;
-		sum += data->at(data, index + i) * kernel;
+		sum += data->at(index + i, data->context) * kernel;
 	}
 	return sum / kernelSum;
 }