Add support for gapless looping music.

OpenRA.Game/Sound/Sound.cs

@@ -137,6 +137,12 @@ namespace OpenRA
 			soundEngine.Volume = 1f;
 		}
 
+		public void SetMusicLooped(bool loop)
+		{
+			Game.Settings.Sound.Repeat = loop;
+			soundEngine.SetSoundLooping(loop, music);
+		}
+
 		public bool DisableAllSounds { get; set; }
 		public bool DisableWorldSounds { get; set; }
 		public ISound Play(SoundType type, string name) { return Play(type, null, name, true, WPos.Zero, 1f); }
@@ -202,11 +208,6 @@ namespace OpenRA
 		public bool MusicPlaying { get; private set; }
 		public MusicInfo CurrentMusic => currentMusic;
 
-		public void PlayMusic(MusicInfo m)
-		{
-			PlayMusicThen(m, () => { });
-		}
-
 		public void PlayMusicThen(MusicInfo m, Action then)
 		{
 			if (m == null || !m.Exists)
@@ -221,13 +222,21 @@ namespace OpenRA
 				return;
 			}
 
+			PlayMusic(m, Game.Settings.Sound.Repeat);
+		}
+
+		public void PlayMusic(MusicInfo m, bool looped = false)
+		{
+			if (m == null || !m.Exists)
+				return;
+
 			StopMusic();
 
 			Func<ISoundFormat, ISound> stream = soundFormat => soundEngine.Play2DStream(
 				soundFormat.GetPCMInputStream(), soundFormat.Channels, soundFormat.SampleBits, soundFormat.SampleRate,
-				false, true, WPos.Zero, MusicVolume * m.VolumeModifier);
-			music = LoadSound(m.Filename, stream);
+				looped, true, WPos.Zero, MusicVolume * m.VolumeModifier);
 
+			music = LoadSound(m.Filename, stream);
 			if (music == null)
 			{
 				onMusicComplete = null;

OpenRA.Game/Sound/SoundDevice.cs

@@ -28,6 +28,7 @@ namespace OpenRA
 		void StopAllSounds();
 		void SetListenerPosition(WPos position);
 		void SetSoundVolume(float volume, ISound music, ISound video);
+		void SetSoundLooping(bool looping, ISound sound);
 	}
 
 	public class SoundDevice

OpenRA.Mods.Common/Traits/World/MusicPlaylist.cs

@@ -162,13 +162,15 @@ namespace OpenRA.Mods.Common.Traits
 			if (!SongExists(currentSong) || (CurrentSongIsBackground && IsBackgroundMusicMuted))
 				return;
 
-			Game.Sound.PlayMusicThen(currentSong, () =>
-			{
-				if (!CurrentSongIsBackground && !Game.Settings.Sound.Repeat)
-					currentSong = GetNextSong();
+			Game.Sound.PlayMusicThen(currentSong, PlayNextSong);
+		}
 
-				Play();
-			});
+		void PlayNextSong()
+		{
+			if (!CurrentSongIsBackground)
+				currentSong = GetNextSong();
+
+			Play();
 		}
 
 		public void Play(MusicInfo music)

OpenRA.Mods.Common/Widgets/Logic/MusicPlayerLogic.cs

@@ -78,7 +78,7 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 
 			var repeatCheckbox = panel.Get<CheckboxWidget>("REPEAT");
 			repeatCheckbox.IsChecked = () => Game.Settings.Sound.Repeat;
-			repeatCheckbox.OnClick = () => Game.Settings.Sound.Repeat ^= true;
+			repeatCheckbox.OnClick = () => Game.Sound.SetMusicLooped(!Game.Settings.Sound.Repeat);
 			repeatCheckbox.IsDisabled = () => musicPlaylist.CurrentSongIsBackground;
 
 			panel.Get<LabelWidget>("TIME_LABEL").GetText = () =>

OpenRA.Platforms.Default/DummySoundEngine.cs

@@ -56,6 +56,7 @@ namespace OpenRA.Platforms.Default
 		public void StopSound(ISound sound) { }
 		public void StopAllSounds() { }
 		public void SetListenerPosition(WPos position) { }
+		public void SetSoundLooping(bool looping, ISound sound) { }
 		public void Dispose() { }
 	}
 

OpenRA.Platforms.Default/OpenAlSoundEngine.cs

@@ -66,7 +66,7 @@ namespace OpenRA.Platforms.Default
 			if (devicesPtr == IntPtr.Zero || AL10.alGetError() != AL10.AL_NO_ERROR)
 			{
 				Log.Write("sound", "Failed to query OpenAL device list using {0}", label);
-				return new string[0];
+				return Array.Empty<string>();
 			}
 
 			var devices = new List<string>();
@@ -103,7 +103,7 @@ namespace OpenRA.Platforms.Default
 			if (ALC11.alcIsExtensionPresent(IntPtr.Zero, "ALC_ENUMERATION_EXT"))
 				return QueryDevices("ALC_ENUMERATION_EXT", ALC10.ALC_DEVICE_SPECIFIER);
 
-			return new string[] { };
+			return Array.Empty<string>();
 		}
 
 		internal static int MakeALFormat(int channels, int bits)
@@ -137,8 +137,7 @@ namespace OpenRA.Platforms.Default
 
 			for (var i = 0; i < PoolSize; i++)
 			{
-				var source = 0U;
-				AL10.alGenSources(1, out source);
+				AL10.alGenSources(1, out var source);
 				if (AL10.alGetError() != AL10.AL_NO_ERROR)
 				{
 					Log.Write("sound", "Failed generating OpenAL source {0}", i);
@@ -346,6 +345,11 @@ namespace OpenRA.Platforms.Default
 			AL10.alListenerf(EFX.AL_METERS_PER_UNIT, .01f);
 		}
 
+		public void SetSoundLooping(bool looping, ISound sound)
+		{
+			((OpenAlSound)sound)?.SetLooping(looping);
+		}
+
 		~OpenAlSoundEngine()
 		{
 			Dispose(false);
@@ -518,6 +522,14 @@ namespace OpenRA.Platforms.Default
 			StopSource();
 			AL10.alSourcei(Source, AL10.AL_BUFFER, 0);
 		}
+
+		public void SetLooping(bool looping)
+		{
+			if (done)
+				return;
+
+			AL10.alSourcei(Source, AL10.AL_LOOPING, looping ? AL10.AL_TRUE : AL10.AL_FALSE);
+		}
 	}
 
 	class OpenAlAsyncLoadSound : OpenAlSound