Seamless Fading Loop in Freeplay Previews

Author: Raltyro

source/funkin/play/song/Song.hx

@@ -329,6 +329,8 @@ class Song implements IPlayStateScriptedClass implements IRegistryEntry<SongMeta
         difficulty.difficultyRating = metadata.playData.ratings.get(diffId) ?? 0;
         difficulty.album = metadata.playData.album;
         difficulty.stickerPack = metadata.playData.stickerPack;
+        difficulty.previewStart = metadata.playData.previewStart;
+        difficulty.previewEnd = metadata.playData.previewEnd;
 
         difficulty.stage = metadata.playData.stage;
         difficulty.noteStyle = metadata.playData.noteStyle;
@@ -793,6 +795,8 @@ class SongDifficulty
   public var difficultyRating:Int = 0;
   public var album:Null<String> = null;
   public var stickerPack:Null<String> = null;
+  public var previewStart:Int = 0;
+  public var previewEnd:Int = 15000;
 
   public function new(song:Song, diffId:String, variation:String)
   {

source/funkin/ui/freeplay/FreeplayState.hx

@@ -44,7 +44,7 @@ import funkin.ui.AtlasText;
 import funkin.ui.FullScreenScaleMode;
 import funkin.ui.MusicBeatSubState;
 import funkin.ui.freeplay.backcards.*;
-import funkin.ui.freeplay.components.DifficultySprite;
+import funkin.ui.freeplay.components.*;
 import funkin.ui.freeplay.charselect.PlayableCharacter;
 import funkin.ui.mainmenu.MainMenuState;
 import funkin.ui.story.Level;
@@ -272,6 +272,8 @@ class FreeplayState extends MusicBeatSubState
 
   public var freeplayArrow:Null<FlxText>;
 
+  var previewMusicData:Null<PreviewMusicData> = null;
+
   public function new(?params:FreeplayStateParams, ?stickers:StickerSubState)
   {
     var fetchPlayableCharacter = function():PlayableCharacter
@@ -2190,6 +2192,8 @@ class FreeplayState extends MusicBeatSubState
     FlxG.cameras.remove(funnyCam);
     // Cancel all song preview timers just in case a preview loads after we exit.
     clearPreviews();
+    // Destroy the preview music data.
+    previewMusicData?.destroy();
   }
 
   function goBack():Void
@@ -2951,6 +2955,9 @@ class FreeplayState extends MusicBeatSubState
   {
     if (daSongCapsule == null) daSongCapsule = currentCapsule;
 
+    // Make sure the player is still hovering over the song we want to load preview for
+    if (!daSongCapsule.selected) return;
+
     var previewVolume:Float = 0.7;
     if (dj != null) previewVolume *= dj.getMusicPreviewMult();
 
@@ -2969,8 +2976,6 @@ class FreeplayState extends MusicBeatSubState
     }
     else
     {
-      // Make sure the player is still hovering over the song we want to load preview for
-      if (!daSongCapsule.selected) return;
       var previewSong:Null<Song> = daSongCapsule?.freeplayData?.data;
       if (previewSong == null) return;
 
@@ -2990,35 +2995,26 @@ class FreeplayState extends MusicBeatSubState
       instSuffix = (instSuffix != '') ? '-$instSuffix' : '';
       // trace('Attempting to play partial preview: ${previewSong.id}:${instSuffix}');
 
-      FunkinSound.playMusic(previewSong.id, {
-        startingVolume: 0.0,
-        overrideExisting: true,
-        restartTrack: false,
-        mapTimeChanges: false, // The music metadata is not alongside the audio file so this won't work.
-        pathsFunction: INST,
-        suffix: instSuffix,
-        partialParams: {
-          loadPartial: true,
-          start: 0,
-          end: 0.2
-        },
-        onLoad: function()
-        {
-          FlxG.sound.music.fadeIn(2, 0, previewVolume);
-
-          var fadeStart:Float = (FlxG.sound.music.length / 1000) - 2;
+      if (FlxG.sound.music == null)
+      {
+        FunkinSound.setMusic(FunkinSound.load(null));
+      }
 
-          previewTimers.push(new FlxTimer().start(fadeStart, function(_)
-          {
-            FlxG.sound.music.fadeOut(2, 0);
-          }));
+      if (previewMusicData == null) previewMusicData = new PreviewMusicData();
+      previewMusicData.setAssetPath(Paths.inst(previewSong.id, instSuffix), songDifficulty?.previewStart, songDifficulty?.previewEnd, true,
+        function(musicData:PreviewMusicData)
+      {
+        // Check again if it's still selected.
+        if (!daSongCapsule.selected) return;
 
-          previewTimers.push(new FlxTimer().start(FlxG.sound.music.length / 1000, function(_)
-          {
-            playCurSongPreview();
-          }));
-        },
+        FlxG.sound.music.fadeTween?.cancel();
+        FlxG.sound.music.unload();
+        FlxG.sound.music.loadEmbedded(musicData);
+        FlxG.sound.music.volume = previewVolume;
+        FlxG.sound.music.looped = true;
+        FlxG.sound.music.play(true, 0);
       });
+
       if (songDifficulty != null)
       {
         Conductor.instance.mapTimeChanges(songDifficulty.timeChanges);