Fix SFX and MIDI music not playing on Android

snd_start_digital() opened two separate SDL audio devices - a raw one
for cutscene/audiolog audio and a second via Mix_OpenAudio() for
SFX/MIDI - but Android's audio backends only ever allow one open
non-capture device, so the second open always failed silently.

- Consolidate onto a single Mix_OpenAudio() device; cutscene/audiolog
  PCM is now mixed into its output via Mix_SetPostMix() instead of a
  dedicated device (16-android-audio-single-device.patch)
- Add SDL_GetError() to the failure log so a future open failure is
  actually diagnosable (15-android-audio-error-detail.patch)
- Make NativeMidiInit() report failure on platforms with no real
  implementation (Android included), instead of silently claiming
  success without opening anything (17-android-native-midi-unsupported.patch)
- Strengthen the OpenSL ES driver hint to SDL_HINT_OVERRIDE and log the
  active audio driver as a standing diagnostic (05-android-audio-driver.patch)

README.md

@@ -383,10 +383,14 @@ each one does:
   emulation) for real GLES-native equivalents: a custom `pointSize`
   uniform, a shader-side alpha discard, and native point-sprite
   rasterization.
-- **`05-android-audio-driver.patch`** - forces SDL2's older OpenSL ES
+- **`05-android-audio-driver.patch`** - forces SDL2's OpenSL ES audio
-  audio backend instead of AAudio, because AAudio only allows one open
+  backend instead of AAudio via
-  playback device and the engine opens two (cutscene audio plus
+  `SDL_SetHintWithPriority(..., SDL_HINT_OVERRIDE)` (so nothing else can
-  `Mix_OpenAudio` for SFX/MIDI).
+  take precedence and silently leave AAudio selected), and logs the
+  actual `SDL_GetCurrentAudioDriver()` result right after `SDL_Init()`
+  as a standing on-device diagnostic. Does not by itself fix SFX/MIDI
+  playback - see `16-android-audio-single-device.patch` and README 5.5.3
+  for the actual cause and fix.
 - **`06-android-resize-event.patch`** - makes the engine react to
   `SDL_WINDOWEVENT_RESIZED`, not just `SIZE_CHANGED`, since Android's SDL
   backend only ever sends the former for surface-driven resizes.
@@ -434,6 +438,32 @@ each one does:
   inherited non-default unpack state left behind elsewhere in the frame
   and misread every row. Fixed by resetting both to the packed defaults
   immediately before this upload.
+- **`15-android-audio-error-detail.patch`** - `snd_start_digital()`'s
+  `Mix_OpenAudio()` failure only logged a fixed string, not the actual
+  reason. Adds `SDL_GetError()` to the log line so the next on-device
+  failure reports the real underlying error.
+- **`16-android-audio-single-device.patch`** - fixes SFX/MIDI music not
+  playing (see README 5.5.3). `snd_start_digital()` opened two SDL audio
+  devices: a raw `SDL_OpenAudioDevice()` for cutscene/audiolog audio and
+  a second one via `Mix_OpenAudio()` for SFX/MIDI - SDL's Android audio
+  backends only ever allow one open non-capture device, so the second
+  open always failed. Removes the raw device entirely and feeds cutscene/
+  audiolog PCM into the `Mix_OpenAudio()` device's output instead, via
+  `Mix_SetPostMix()` (mixing in rather than overwriting, so it doesn't
+  silence any SFX/MIDI music playing at the same time). `cutsloop.c`'s
+  and `audiolog.c`'s `SDL_PauseAudioDevice()` calls (no longer meaningful
+  without a dedicated device) are removed; the cutscene-audio-stream
+  pointer swaps they guarded are now protected by `SDL_LockAudio()`/
+  `SDL_UnlockAudio()` instead, since SDL_mixer's audio thread now reads
+  that pointer continuously via the post-mix hook.
+- **`17-android-native-midi-unsupported.patch`** - `NativeMidiInit()` in
+  `MusicDevice.c` has real implementations only under `#ifdef WIN32` and
+  `#elif defined(USE_ALSA)`; on every other platform (Android included)
+  it fell through to `return 0` (success) without ever opening a device,
+  so a `midi-backend` preference of "Native" (see README 5.5.4) played
+  silently forever instead of falling back. Adds an `#else` branch that
+  returns failure and logs a `WARN`, so `InitDecXMI()`'s existing
+  fallback-to-dummy-driver logic actually triggers.
 
 `android/gl4es-patches/`:
 
@@ -517,10 +547,58 @@ left behind elsewhere in the frame and misreads every row - a diagonal
 shear/banding pattern. Menus never trigger it because nothing in the
 menu-only code paths sets a custom unpack stride first.
 
-**Fix** (`14-android-quad-unpack-state.patch`): explicitly reset both
+#### 5.5.3. In-game SFX and MIDI music didn't play
-`GL_UNPACK_ROW_LENGTH` and `GL_UNPACK_ALIGNMENT` to their tightly-packed
+
-values immediately before this `glTexImage2D` call, removing the
+Intro cutscene audio played correctly, but in-game SFX and MIDI/background
-dependency on whatever GL state preceded it.
+music never played, on-device.
+
+**Root cause:** `snd_start_digital()` in `engine/src/MacSrc/SDLSound.c`
+opened two separate SDL audio devices - a raw `SDL_OpenAudioDevice()`
+call (used for cutscene/movie audio, always succeeded) and a second
+device via `Mix_OpenAudio()` (used for SFX and, via `Mix_HookMusic`,
+MIDI music - always failed, `SDL_GetError()` reporting "Audio device
+already open"). SDL's Android audio backends (both AAudio and OpenSL ES)
+only ever allow one open non-capture device - forcing OpenSL ES instead
+of AAudio (`05-android-audio-driver.patch`) doesn't change this, since
+the restriction isn't backend-specific.
+
+**Fix (`16-android-audio-single-device.patch`):** removed the raw
+`SDL_OpenAudioDevice()` call entirely. Cutscene/audiolog PCM (previously
+delivered via that device's own callback) is now mixed into the single
+`Mix_OpenAudio()` device's output via `Mix_SetPostMix()`, additively
+(`SDL_MixAudioFormat`) rather than overwritten, so SFX/MIDI music
+already mixed into the buffer isn't silenced whenever a cutscene or
+audiolog plays. The stream-pointer swaps in `cutsloop.c`/`audiolog.c`
+that used to be guarded by pausing the now-removed device are guarded by
+`SDL_LockAudio()`/`SDL_UnlockAudio()` instead, since the post-mix hook
+runs continuously on SDL_mixer's own audio thread.
+
+#### 5.5.4. MIDI music silent even after audio otherwise worked
+
+After fixing 5.5.3, SFX and cutscene audio played correctly, but MIDI
+background music was still silent, with logcat showing `Creating native
+MIDI device` instead of `Creating FluidSynth MIDI device`.
+
+**Root cause:** the engine's `midi-backend` preference (`0` = ADLMIDI,
+`1` = Native, `2` = FluidSynth) is persisted in a `prefs.txt` file in the
+app's private storage, which Android retains across every APK
+reinstall/upgrade (only a full uninstall clears it). A stale value of
+`1` (Native) from earlier testing was carried forward through every
+rebuild this whole session. `SetDefaultPrefs()` (`Prefs.c`) does default
+to `2` (FluidSynth) whenever `USE_FLUIDSYNTH` is defined, which it
+always has been for this build - the default was never wrong, only the
+persisted override. `NativeMidiInit()` has no real implementation on
+Android (see `17-android-native-midi-unsupported.patch`), so it silently
+reported success without opening anything.
+
+**Fix:** a full uninstall (not just installing a new build over the old
+one) clears the stale preference, after which MIDI plays correctly.
+`17-android-native-midi-unsupported.patch` additionally makes
+`NativeMidiInit()` report failure on unsupported platforms, so a stale
+"Native" preference falls back to `InitDecXMI()`'s existing dummy-driver
+path (still silent, but with a clear `WARN` in logcat) instead of
+silently reporting success while never opening anything - a much faster
+diagnosis if this ever recurs.
 
 ## 6. License
 

android/engine-patches/05-android-audio-driver.patch

@@ -1,6 +1,6 @@
 --- a/src/MacSrc/Shock.c
 +++ b/src/MacSrc/Shock.c
-@@ -162,6 +162,17 @@
+@@ -162,9 +162,26 @@
  void InitSDL() {
      SDL_SetHint(SDL_HINT_NO_SIGNAL_HANDLERS, "1");
      SDL_SetHint(SDL_HINT_RENDER_DRIVER, "opengl");
@@ -12,9 +12,18 @@
 +    // src/audio/aaudio/SDL_aaudio.c). SDLSound.c opens two: one directly via
 +    // SDL_OpenAudioDevice() for cutscene audio, one via Mix_OpenAudio() for
 +    // SFX/MIDI. The older OpenSL ES backend has no such limitation, so force
-+    // it instead of AAudio.
++    // it instead of AAudio. Uses SDL_HINT_OVERRIDE priority so nothing set
-+    SDL_SetHint(SDL_HINT_AUDIODRIVER, "openslES");
++    // earlier (or by SDL/the platform) can take precedence over it.
++    SDL_SetHintWithPriority(SDL_HINT_AUDIODRIVER, "openslES", SDL_HINT_OVERRIDE);
 +#endif
      if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER | SDL_INIT_AUDIO) < 0) {
          DEBUG("%s: Init failed", __FUNCTION__);
      }
++#ifdef __ANDROID__
++    // Standing diagnostic: reports which audio driver SDL actually selected,
++    // to confirm the openslES override above took effect on-device.
++    INFO("SDL audio driver: %s", SDL_GetCurrentAudioDriver());
++#endif
+ 
+     // TODO: figure out some universal set of settings that work...
+ #ifdef __ANDROID__

android/engine-patches/15-android-audio-error-detail.patch

@@ -0,0 +1,11 @@
+--- a/src/MacSrc/SDLSound.c
++++ b/src/MacSrc/SDLSound.c
+@@ -42,7 +42,7 @@
+     }
+
+     if (Mix_OpenAudio(48000, AUDIO_S16SYS, 2, 2048) < 0) {
+-        ERROR("%s: Couldn't open audio device", __FUNCTION__);
++        ERROR("%s: Couldn't open audio device: %s", __FUNCTION__, SDL_GetError());
+     }
+
+     Mix_AllocateChannels(SND_MAX_SAMPLES);

android/engine-patches/16-android-audio-single-device.patch

@@ -0,0 +1,181 @@
+--- a/src/MacSrc/SDLSound.c
++++ b/src/MacSrc/SDLSound.c
+@@ -19,24 +19,6 @@
+ 
+     // Startup the sound system
+ 
+-    SDL_AudioSpec spec, obtained;
+-    spec.freq = 48000;
+-    spec.format = AUDIO_S16SYS;
+-    spec.channels = 2;
+-    spec.samples = 2048;
+-    spec.callback = AudioStreamCallback;
+-    spec.userdata = (void *)&cutscene_audiostream;
+-
+-    extern SDL_AudioDeviceID device;
+-    device = SDL_OpenAudioDevice(NULL, 0, &spec, &obtained, 0);
+-
+-    if (device == 0) {
+-        ERROR("Could not open SDL audio: %s", SDL_GetError());
+-    } else {
+-        INFO("Opened Music Stream, deviceID %d, freq %d, size %d, format %d, channels %d, samples %d", device,
+-             obtained.freq, obtained.size, obtained.format, obtained.channels, obtained.samples);
+-    }
+-
+     if (Mix_Init(MIX_INIT_MP3) < 0) {
+         ERROR("%s: Init failed", __FUNCTION__);
+     }
+@@ -50,10 +32,18 @@
+     Mix_HookMusic(MusicCallback, (void *)&MusicDev);
+     Mix_VolumeMusic(MIX_MAX_VOLUME); // use max volume for music stream
+ 
++    // Cutscene/audiolog playback (AudioStreamCallback, see cutsloop.c) used to
++    // run through its own SDL_OpenAudioDevice() device, separate from this
++    // one - SDL only ever allows one open non-capture device on Android's
++    // audio backends, so that second open always failed with "Audio device
++    // already open" and both SFX and MIDI music (both routed through this
++    // Mix_OpenAudio device) silently never played. Mixed into this device's
++    // post-mix stage instead, so there is only ever one device open.
++    Mix_SetPostMix(AudioStreamCallback, (void *)&cutscene_audiostream);
++
+     InitReadXMI();
+ 
+     atexit(Mix_CloseAudio);
+-    atexit(SDL_CloseAudio);
+ 
+     return OK;
+ }
+--- a/src/MacSrc/Shock.c
++++ b/src/MacSrc/Shock.c
+@@ -60,8 +60,6 @@
+ SDL_Palette *sdlPalette;
+ SDL_Renderer *renderer;
+ 
+-SDL_AudioDeviceID device;
+-
+ int num_args;
+ char **arg_values;
+ 
+--- a/src/GameSrc/cutsloop.c
++++ b/src/GameSrc/cutsloop.c
+@@ -83,15 +83,25 @@
+ extern char FrnSubtitle[256];
+ extern char GerSubtitle[256];
+ 
+-extern SDL_AudioDeviceID device;
+-
+-
++// Runs as SDL_mixer's post-mix hook (see snd_start_digital() in
++// SDLSound.c) rather than a dedicated SDL audio device's callback, so
++// SFX/MIDI music sharing the same device are already mixed into `stream`
++// by the time this runs - mix in rather than overwrite, so they aren't
++// silenced whenever a cutscene or audiolog is playing.
+ void AudioStreamCallback(void *userdata, unsigned char *stream, int len)
+ {
++  static Uint8 mixbuf[MOVIE_DEFAULT_BLOCKLEN * 4];
+   SDL_AudioStream *as = *(SDL_AudioStream **)userdata;
+ 
+-  if (as != NULL && SDL_AudioStreamAvailable(as) > 0)
+-    SDL_AudioStreamGet(as, stream, len);
++  if (as == NULL || SDL_AudioStreamAvailable(as) <= 0)
++    return;
++
++  if (len > (int)sizeof(mixbuf))
++    len = (int)sizeof(mixbuf);
++
++  int got = SDL_AudioStreamGet(as, mixbuf, len);
++  if (got > 0)
++    SDL_MixAudioFormat(stream, mixbuf, AUDIO_S16SYS, got, SDL_MIX_MAXVOLUME);
+ }
+ 
+ 
+@@ -153,11 +163,13 @@
+ 
+   if (cutscene_audiostream != NULL)
+   {
+-    SDL_PauseAudioDevice(device, 1);
+-    SDL_Delay(1);
+-
++    // AudioStreamCallback (SDL_mixer's post-mix hook) runs continuously on
++    // SDL_mixer's own audio thread and reads this pointer - lock around
++    // freeing it so that thread can't be mid-read when it's freed.
++    SDL_LockAudio();
+     SDL_FreeAudioStream(cutscene_audiostream);
+     cutscene_audiostream = NULL;
++    SDL_UnlockAudio();
+ 
+     if (cutscene_audiobuffer)
+     {
+@@ -184,8 +196,6 @@
+ 
+   if (cutscene_audiostream)
+   {
+-    SDL_PauseAudioDevice(device, 0);
+-  
+     if (cutscene_audiobuffer_size > 0)
+     {
+       // === adjust volume in buffer here ===
+@@ -325,10 +335,9 @@
+ 
+   if (sfx_on)
+   {
+-    SDL_PauseAudioDevice(device, 1);
+-    SDL_Delay(1);
+-
++    SDL_LockAudio();
+     cutscene_audiostream = SDL_NewAudioStream(AUDIO_U8, 1, fix_int(amovie->a.sampleRate), AUDIO_S16SYS, 2, 48000);
++    SDL_UnlockAudio();
+ 
+     cutscene_audiobuffer_pos = cutscene_audiobuffer;
+   }
+--- a/src/GameSrc/audiolog.c
++++ b/src/GameSrc/audiolog.c
+@@ -61,8 +61,6 @@
+ extern uchar curr_alog_vol;
+ extern char which_lang;
+ 
+-extern SDL_AudioDeviceID device;
+-
+ errtype audiolog_init(void) { return OK; }
+ 
+ errtype audiolog_play(int email_id) {
+@@ -114,10 +112,9 @@
+ 
+     DEBUG("%s: Playing email", __FUNCTION__);
+ 
+-    SDL_PauseAudioDevice(device, 1);
+-    SDL_Delay(1);
+-
++    SDL_LockAudio();
+     cutscene_audiostream = SDL_NewAudioStream(AUDIO_U8, 1, fix_int(palog->a.sampleRate), AUDIO_S16SYS, 2, 48000);
++    SDL_UnlockAudio();
+ 
+     audiolog_audiobuffer_pos = audiolog_audiobuffer;
+ 
+@@ -150,11 +147,14 @@
+     }
+ 
+     if (cutscene_audiostream != NULL) {
+-        SDL_PauseAudioDevice(device, 1);
+-        SDL_Delay(1);
+-
++        // AudioStreamCallback (SDL_mixer's post-mix hook, see cutsloop.c)
++        // runs continuously on SDL_mixer's own audio thread and reads this
++        // pointer - lock around freeing it so that thread can't be
++        // mid-read when it's freed.
++        SDL_LockAudio();
+         SDL_FreeAudioStream(cutscene_audiostream);
+         cutscene_audiostream = NULL;
++        SDL_UnlockAudio();
+ 
+         if (audiolog_audiobuffer) {
+             free(audiolog_audiobuffer);
+@@ -177,8 +177,6 @@
+ 
+ errtype audiolog_loop_callback(void) {
+     if (cutscene_audiostream) {
+-        SDL_PauseAudioDevice(device, 0);
+-
+         if (audiolog_audiobuffer_size > 0) {
+             int i, vol = curr_alog_vol * 127 / 100; // convert from 0-100 to 0-127
+ 

android/engine-patches/17-android-native-midi-unsupported.patch

@@ -0,0 +1,17 @@
+--- a/src/MusicSrc/MusicDevice.c
++++ b/src/MusicSrc/MusicDevice.c
+@@ -569,6 +569,14 @@
+     // connected
+     ndev->dev.isOpen = 1;
+     ndev->dev.outputIndex = outputIndex;
++#else
++    // No native MIDI backend implemented for this platform (e.g. Android) -
++    // report failure so InitDecXMI()'s caller falls back to another device
++    // instead of treating an unopened device as successfully initialized.
++    (void)outputIndex;
++    (void)samplerate;
++    WARN("NativeMidiInit(): native MIDI is not implemented on this platform");
++    return -1;
+ #endif
+     // suppress compiler warnings
+     (void)outputIndex;