From c4888bea71326f7a69e8214af0d9c2a62a60b887 Mon Sep 17 00:00:00 2001
From: skal <pascal.massimino@gmail.com>
Date: Wed, 4 Feb 2026 13:08:13 +0100
Subject: feat(audio): Implement audio backend abstraction (Task #51.1)

Created interface-based audio backend system to enable testing without
hardware. This is the foundation for robust tracker timing verification.

Changes:
- Created AudioBackend interface with init/start/shutdown methods
- Added test-only hooks: on_voice_triggered() and on_frames_rendered()
- Moved miniaudio implementation to MiniaudioBackend class
- Refactored audio.cc to use backend abstraction with auto-fallback
- Added time tracking to synth.cc (elapsed time from rendered frames)
- Created test_audio_backend.cc to verify backend injection works
- Fixed audio test linking to include util/procedural dependencies

All test infrastructure guarded by #if !defined(STRIP_ALL) for zero
size impact on final build. Production path unchanged, 100% backward
compatible. All 13 tests pass.

handoff(Claude): Task #51.1 complete, audio backend abstraction ready

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
---
 src/audio/miniaudio_backend.cc | 70 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 src/audio/miniaudio_backend.cc

(limited to 'src/audio/miniaudio_backend.cc')

diff --git a/src/audio/miniaudio_backend.cc b/src/audio/miniaudio_backend.cc
new file mode 100644
index 0000000..d2563c5
--- /dev/null
+++ b/src/audio/miniaudio_backend.cc
@@ -0,0 +1,70 @@
+// This file is part of the 64k demo project.
+// It implements the production audio backend using miniaudio.
+// Moved from audio.cc to enable backend abstraction for testing.
+
+#include "miniaudio_backend.h"
+#include "synth.h"
+#include <stdio.h>
+
+// Static callback for miniaudio (C API requirement)
+void MiniaudioBackend::audio_callback(ma_device* pDevice, void* pOutput,
+                                       const void* pInput,
+                                       ma_uint32 frameCount) {
+  (void)pDevice;
+  (void)pInput;
+  float* fOutput = (float*)pOutput;
+  synth_render(fOutput, (int)frameCount);
+}
+
+MiniaudioBackend::MiniaudioBackend() : initialized_(false) {
+}
+
+MiniaudioBackend::~MiniaudioBackend() {
+  if (initialized_) {
+    shutdown();
+  }
+}
+
+void MiniaudioBackend::init() {
+  if (initialized_) {
+    return;
+  }
+
+  ma_device_config config = ma_device_config_init(ma_device_type_playback);
+  config.playback.format = ma_format_f32;
+  config.playback.channels = 2;
+  config.sampleRate = 32000;
+  config.dataCallback = MiniaudioBackend::audio_callback;
+  config.pUserData = this;
+
+  if (ma_device_init(NULL, &config, &device_) != MA_SUCCESS) {
+    printf("Failed to open playback device.\n");
+    return;
+  }
+
+  initialized_ = true;
+}
+
+void MiniaudioBackend::start() {
+  if (!initialized_) {
+    printf("Cannot start: backend not initialized.\n");
+    return;
+  }
+
+  if (ma_device_start(&device_) != MA_SUCCESS) {
+    printf("Failed to start playback device.\n");
+    ma_device_uninit(&device_);
+    initialized_ = false;
+    return;
+  }
+}
+
+void MiniaudioBackend::shutdown() {
+  if (!initialized_) {
+    return;
+  }
+
+  ma_device_stop(&device_);
+  ma_device_uninit(&device_);
+  initialized_ = false;
+}
-- 
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