EXPERIMENT: up the OpenAlSource's MaxQueue

Our setting is done wrong, because a) it's constants regardless of situation, b) it counts only number of buffers instead of total length (or size).
First of all, buffers may be very small, and then if OpenAlSource is used by the system that does not care about it not being able to queue, then the playback will be skipping chunks.

The low queue limit was necessary mostly to workaround effects lag, such as setting speed. This may be resolved differently.

Engine/media/audio/audio_core.cpp

@@ -77,7 +77,9 @@ AudioCoreSlot::AudioCoreSlot(int handle, std::unique_ptr<SDLDecoder> decoder)
     : handle_(handle), _decoder(std::move(decoder))
 {
     _source = std::make_unique<OpenAlSource>(
-        _decoder->GetFormat(), _decoder->GetChannels(), _decoder->GetFreq());
+        _decoder->GetFormat(), _decoder->GetChannels(), _decoder->GetFreq(),
+        2 /* TODO: make this a constant,
+          and add comment explaining why we keep this queue limit low for now */);
 }
 
 void AudioCoreSlot::Init()

Engine/media/audio/openalsource.cpp

@@ -95,12 +95,13 @@ static struct
 // OpenAlSource
 //-----------------------------------------------------------------------------
 
-OpenAlSource::OpenAlSource(SDL_AudioFormat format, int channels, int freq)
+OpenAlSource::OpenAlSource(SDL_AudioFormat format, int channels, int freq, uint32_t max_queue)
 {
     _inputFmt.format = format;
     _inputFmt.channels = static_cast<Uint8>(channels);
     _inputFmt.rate = freq;
-    _alFormat = OpenAlFormatFromSDLFormat(_inputFmt, _recvFmt);;
+    _alFormat = OpenAlFormatFromSDLFormat(_inputFmt, _recvFmt);
+    _maxQueue = max_queue;
     alGenSources(1, &_source);
     dump_al_errors();
     _resampler.Setup(_inputFmt, _recvFmt);
@@ -156,7 +157,7 @@ size_t OpenAlSource::PutData(const SoundBuffer &data)
 {
     Unqueue();
     // If queue is full, bail out
-    if (_queued >= MaxQueue) { return 0u; }
+    if (_queued >= _maxQueue) { return 0u; }
     // Input buffer is empty?
     if (!data.Data || (data.Size == 0)) { return 0u; }
     // Check for free buffers, generate more if necessary

Engine/media/audio/openalsource.h

@@ -33,12 +33,9 @@ namespace Engine
 class OpenAlSource
 {
 public:
-    // Max sound buffers to queue before/during processing
-    static const ALuint MaxQueue = 2;
-
     // Initializes Al source for the given format; if there's no direct format equivalent
     // found, setups a resampler.
-    OpenAlSource(SDL_AudioFormat format, int channels, int freq);
+    OpenAlSource(SDL_AudioFormat format, int channels, int freq, uint32_t max_queue = 1024u);
     OpenAlSource(OpenAlSource&& src);
     ~OpenAlSource();
 
@@ -87,7 +84,13 @@ class OpenAlSource
     PlaybackState _playState = PlayStateInitial;
     float _speed = 1.f; // change in playback rate
     float _predictTs = 0.f; // next timestamp prediction
-    unsigned _queued = 0u;
+    // Max sound buffers to queue during processing.
+    // TODO: replace limit of buffer count with limit of memory and/or duration.
+    // TODO: add a comment explaining why do we have to set very small queue limit
+    // for regular audio slot play (to decrease custom effects lag),
+    // alternatively have this logic externally to OpenALSource, somewhere in AudioCoreSlot.
+    uint32_t _maxQueue = 1024u;
+    uint32_t _queued = 0u;
 
     // SDL resampler state, in case dynamic resampling in necessary
     SDLResampler _resampler;

Engine/media/video/video.cpp

@@ -36,9 +36,10 @@
 #include "gfx/ddb.h"
 #include "gfx/graphicsdriver.h"
 #include "main/game_run.h"
-#include "util/stream.h"
 #include "media/audio/audio_system.h"
 #include "media/audio/openal.h"
+#include "util/memory_compat.h"
+#include "util/stream.h"
 
 using namespace AGS::Common;
 using namespace AGS::Engine;
@@ -73,7 +74,7 @@ HError VideoPlayer::Open(const String &name, int flags)
     {
         if ((_audioFormat > 0) && (_audioChannels > 0) && (_audioFreq > 0))
         {
-            _audioOut.reset(new OpenAlSource(_audioFormat, _audioChannels, _audioFreq));
+            _audioOut = std::make_unique<OpenAlSource>(_audioFormat, _audioChannels, _audioFreq);
             _audioOut->Play();
             _wantAudio = true;
         }

Engine/plugin/agsplugin.cpp

@@ -57,6 +57,7 @@
 #include "plugin/plugin_engine.h"
 #include "plugin/plugin_builtin.h"
 #include "util/library.h"
+#include "util/memory_compat.h"
 #include "util/string.h"
 #include "util/wgt2allg.h"
 
@@ -879,7 +880,7 @@ IAGSAudioPlayer *IAGSEngine::OpenAudioPlayer(AGSAudioFormat *in_format, AGSAudio
     int chans = in_format->Channels;
     int freq = in_format->Freq;
     auto *player = new AGSAudioPlayer(
-        std::unique_ptr<OpenAlSource>(new OpenAlSource(sdl_fmt, chans, freq)));
+        std::make_unique<OpenAlSource>(sdl_fmt, chans, freq));
     return player; // todo: should save somewhere for safe close on exit??
 }