Add audio subsystem skeleton with a working Linux PCM playback path

Cross-platform audiostream/audio API with per-platform hooks for
PSP/Dolphin/Linux. Linux is fully wired end-to-end through SDL2
(device open, volume-mixed queueing, finish detection via
SDL_GetQueuedAudioSize) and verified playing a generated test tone
in engine.c. PSP and Dolphin hooks are stubbed for now.

src/dusklinux/CMakeLists.txt

@@ -11,6 +11,7 @@ target_include_directories(${DUSK_LIBRARY_TARGET_NAME}
 
 # Subdirs
 add_subdirectory(asset)
+add_subdirectory(audio)
 add_subdirectory(log)
 add_subdirectory(input)
 if(DUSK_NETWORK)

src/dusklinux/audio/CMakeLists.txt

@@ -0,0 +1,11 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+# Sources
+target_sources(${DUSK_LIBRARY_TARGET_NAME}
+  PUBLIC
+    audiolinux.c
+    audiostreamlinux.c
+)

src/dusklinux/audio/audiolinux.c

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "audiolinux.h"
+#include <SDL2/SDL.h>
+
+errorret_t audioLinuxInit() {
+  if(SDL_InitSubSystem(SDL_INIT_AUDIO) != 0) {
+    errorThrow("Failed to initialize SDL2 audio subsystem: %s", SDL_GetError());
+  }
+
+  errorOk();
+}
+
+errorret_t audioLinuxUpdate() {
+  errorOk();
+}
+
+errorret_t audioLinuxDispose() {
+  SDL_QuitSubSystem(SDL_INIT_AUDIO);
+
+  errorOk();
+}

src/dusklinux/audio/audiolinux.h

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+
+/**
+ * Initializes the Linux-specific audio subsystem state.
+ *
+ * @return Error state if any.
+ */
+errorret_t audioLinuxInit();
+
+/**
+ * Updates the Linux-specific audio subsystem state. Called once per frame.
+ *
+ * @return Error state if any.
+ */
+errorret_t audioLinuxUpdate();
+
+/**
+ * Disposes the Linux-specific audio subsystem state.
+ *
+ * @return Error state if any.
+ */
+errorret_t audioLinuxDispose();

src/dusklinux/audio/audioplatform.h

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "audiolinux.h"
+
+#define audioPlatformInit audioLinuxInit
+#define audioPlatformUpdate audioLinuxUpdate
+#define audioPlatformDispose audioLinuxDispose

src/dusklinux/audio/audiostreamlinux.c

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "audiostreamlinux.h"
+#include "audio/audiostream.h"
+#include "assert/assert.h"
+#include "util/memory.h"
+
+errorret_t audioStreamLinuxInit(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  SDL_AudioSpec desired;
+  memoryZero(&desired, sizeof(SDL_AudioSpec));
+  desired.freq = (int) stream->pcm.sampleRate;
+  desired.format = AUDIO_S16SYS;
+  desired.channels = stream->pcm.channels;
+  desired.samples = 4096;
+
+  stream->platform.device = SDL_OpenAudioDevice(NULL, 0, &desired, NULL, 0);
+  if(stream->platform.device == 0) {
+    errorThrow("Failed to open SDL2 audio device: %s", SDL_GetError());
+  }
+
+  errorOk();
+}
+
+errorret_t audioStreamLinuxDispose(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  SDL_CloseAudioDevice(stream->platform.device);
+
+  errorOk();
+}
+
+errorret_t audioStreamLinuxBuffer(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  uint8_t *mixed = memoryAllocate(stream->dataSize);
+  memoryZero(mixed, stream->dataSize);
+  SDL_MixAudioFormat(
+    mixed, stream->data, AUDIO_S16SYS, (Uint32) stream->dataSize,
+    (stream->volume * SDL_MIX_MAXVOLUME) / 0xFF
+  );
+
+  int queued = SDL_QueueAudio(
+    stream->platform.device, mixed, (Uint32) stream->dataSize
+  );
+  memoryFree(mixed);
+
+  if(queued != 0) {
+    errorThrow("Failed to queue SDL2 audio data: %s", SDL_GetError());
+  }
+
+  SDL_PauseAudioDevice(stream->platform.device, 0);
+
+  errorOk();
+}
+
+bool_t audioStreamLinuxIsFinished(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  return SDL_GetQueuedAudioSize(stream->platform.device) == 0;
+}

src/dusklinux/audio/audiostreamlinux.h

@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include <SDL2/SDL.h>
+
+typedef struct audiostream_s audiostream_t;
+
+typedef struct {
+  SDL_AudioDeviceID device;
+} audiostreamlinux_t;
+
+/**
+ * Initializes the Linux-specific playback state of an audio stream by
+ * opening an SDL2 audio device matching the stream's PCM format.
+ *
+ * @param stream The audio stream to initialize.
+ * @return Error state if any.
+ */
+errorret_t audioStreamLinuxInit(audiostream_t *stream);
+
+/**
+ * Disposes the Linux-specific playback state of an audio stream, closing
+ * its SDL2 audio device.
+ *
+ * @param stream The audio stream to dispose.
+ * @return Error state if any.
+ */
+errorret_t audioStreamLinuxDispose(audiostream_t *stream);
+
+/**
+ * Sends the stream's currently staged PCM data (stream->data) to its SDL2
+ * audio device and starts/resumes playback.
+ *
+ * @param stream The audio stream to output.
+ * @return Error state if any.
+ */
+errorret_t audioStreamLinuxBuffer(audiostream_t *stream);
+
+/**
+ * Checks whether the stream's SDL2 audio device has finished playing all
+ * queued data.
+ *
+ * @param stream The audio stream to check.
+ * @return true if playback has finished, false otherwise.
+ */
+bool_t audioStreamLinuxIsFinished(audiostream_t *stream);

src/dusklinux/audio/audiostreamplatform.h

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "audiostreamlinux.h"
+
+typedef audiostreamlinux_t audiostreamplatform_t;
+
+#define audioStreamPlatformInit audioStreamLinuxInit
+#define audioStreamPlatformDispose audioStreamLinuxDispose
+#define audioStreamPlatformBuffer audioStreamLinuxBuffer
+#define audioStreamPlatformIsFinished audioStreamLinuxIsFinished