audio: switch waveout backend to pull rendering

tests/Components/test_audio_system.cpp

@@ -78,6 +78,60 @@ public:
     uint32 lastSampleRate = 0;
 };
 
+class PullCaptureBackend final : public IAudioBackend {
+public:
+    explicit PullCaptureBackend(const AudioConfig& inConfig) : config(inConfig) {}
+
+    bool Initialize(const AudioConfig& inConfig) override {
+        config = inConfig;
+        return true;
+    }
+
+    void Shutdown() override {}
+
+    std::string GetDeviceName() const override { return "PullCaptureBackend"; }
+    void GetAvailableDevices(std::vector<std::string>& devices) override {
+        devices = {"PullCaptureBackend"};
+    }
+    bool SetDevice(const std::string& deviceName) override { return deviceName == "PullCaptureBackend"; }
+
+    void Start() override { running = true; }
+    void Stop() override { running = false; }
+    void Suspend() override {}
+    void Resume() override {}
+
+    void ProcessAudio(float* buffer, uint32 frameCount, uint32 channels, uint32 sampleRate) override {
+        (void)buffer;
+        (void)frameCount;
+        (void)channels;
+        (void)sampleRate;
+        submissionCount++;
+    }
+
+    bool UsesPullModel() const override { return true; }
+    void SetRenderCallback(RenderCallback callback) override { renderCallback = callback; }
+
+    bool IsRunning() const override { return running; }
+    AudioConfig GetConfig() const override { return config; }
+
+    bool RenderOnce() {
+        if (!renderCallback) {
+            return false;
+        }
+
+        const size_t sampleCount = static_cast<size_t>(config.bufferSize) * config.channels;
+        captured.assign(sampleCount, 0.0f);
+        renderCallback(captured.data(), config.bufferSize, config.channels, config.sampleRate);
+        return true;
+    }
+
+    AudioConfig config{};
+    std::vector<float> captured;
+    RenderCallback renderCallback;
+    bool running = true;
+    uint32 submissionCount = 0;
+};
+
 TEST(AudioSystem, MasterMixerProcessesDirectSources) {
     AudioSystem& system = AudioSystem::Get();
     system.Shutdown();
@@ -318,6 +372,40 @@ TEST(AudioSystem, RenderAudioProducesMixedBlockWithoutBackendSubmission) {
     system.Shutdown();
 }
 
+TEST(AudioSystem, PullBackendRendersViaCallbackWithoutPushSubmission) {
+    AudioSystem& system = AudioSystem::Get();
+    system.Shutdown();
+
+    AudioConfig config;
+    config.sampleRate = 4;
+    config.channels = 1;
+    config.bufferSize = 1;
+
+    auto backend = std::make_unique<PullCaptureBackend>(config);
+    PullCaptureBackend* backendPtr = backend.get();
+    system.SetBackend(std::move(backend));
+    system.SetMasterVolume(0.5f);
+    system.SetMuted(false);
+    system.GetMasterMixer().ClearEffects();
+
+    AudioClip clip = CreateMono16Clip({16384}, 4);
+    AudioSourceComponent source;
+    source.SetSpatialize(false);
+    source.SetClip(&clip);
+    source.Play();
+
+    system.Update(0.0f);
+
+    EXPECT_EQ(backendPtr->submissionCount, 0u);
+    ASSERT_TRUE(backendPtr->RenderOnce());
+    ASSERT_EQ(backendPtr->captured.size(), 1u);
+    EXPECT_NEAR(backendPtr->captured[0], 0.25f, 1e-5f);
+
+    source.Stop();
+    system.SetMasterVolume(1.0f);
+    system.Shutdown();
+}
+
 TEST(AudioSystem, AudioListenerComponentSerializeRoundTripPreservesSettings) {
     AudioSystem& system = AudioSystem::Get();
     system.Shutdown();