Improved grace note positioning

Source/AlphaTab.Test/VisualTests/Features/SpecialNotesTests.cs

@@ -23,6 +23,13 @@ public void GraceNotes()
             RunVisualTest(settings, new[] { 0 }, "TestFiles/Docs/Features/GraceNotes.gp5", "TestFiles/VisualTests/Features/SpecialNotes/GraceNotes.png");
         }
 
+        [TestMethod, AsyncTestMethod]
+        public void GraceNotesAdvanced()
+        {
+            var settings = new Settings();
+            RunVisualTest(settings, new[] { 0, 1 }, "TestFiles/VisualTests/Features/SpecialNotes/GraceNotesAdvanced.gp", "TestFiles/VisualTests/Features/SpecialNotes/GraceNotesAdvanced.png");
+        }
+
         [TestMethod, AsyncTestMethod]
         public void DeadNotes()
         {

Source/AlphaTab/Audio/MidiTickLookup.cs

@@ -221,7 +221,8 @@ public MidiTickLookupFindBeatResult FindBeat(Track[] tracks, int tick)
             for (var b = index + 1; b < beats.Count; b++)
             {
                 var currentBeat = beats[b];
-                if (currentBeat.Start > beat.Start &&
+                if (currentBeat.Beat.GraceType == GraceType.None &&
+                    currentBeat.Start > beat.Start &&
                     trackLookup.ContainsKey(currentBeat.Beat.Voice.Bar.Staff.Track.Index))
                 {
                     nextBeat = currentBeat;
@@ -237,7 +238,8 @@ public MidiTickLookupFindBeatResult FindBeat(Track[] tracks, int tick)
                 for (var b = 0; b < beats.Count; b++)
                 {
                     var currentBeat = beats[b];
-                    if (trackLookup.ContainsKey(currentBeat.Beat.Voice.Bar.Staff.Track.Index))
+                    if (currentBeat.Beat.GraceType == GraceType.None &&
+                        trackLookup.ContainsKey(currentBeat.Beat.Voice.Bar.Staff.Track.Index))
                     {
                         nextBeat = currentBeat;
                         break;

Source/AlphaTab/Model/Voice.cs

@@ -191,21 +191,21 @@ internal void Finish(Settings settings)
                             nonGrace.UpdateDurations();
                         }
 
-                        // grace beats have 1/4 size of the non grace beat following them
-                        var perGraceDuration = nonGrace == null
+                        // grace beats have 1/4 size of the non grace beat preceeding them
+                        var perGraceDisplayDuration = beat.PreviousBeat == null
                             ? Duration.ThirtySecond.ToTicks()
-                            : nonGrace.DisplayDuration / 4 / numberOfGraceBeats;
+                            : beat.PreviousBeat.DisplayDuration / 4 / numberOfGraceBeats;
 
-                        // move all grace beats 
+                        // move all grace beats
                         var graceBeat = Beats[i];
                         for (var j = 0; j < numberOfGraceBeats && graceBeat != null; j++)
                         {
                             graceBeat.Duration = graceDuration;
                             graceBeat.UpdateDurations();
 
                             graceBeat.DisplayStart =
-                                currentDisplayTick - (numberOfGraceBeats - j + 1) * perGraceDuration;
-                            graceBeat.DisplayDuration = perGraceDuration;
+                                currentDisplayTick - (numberOfGraceBeats - j + 1) * perGraceDisplayDuration;
+                            graceBeat.DisplayDuration = perGraceDisplayDuration;
 
                             stolenDuration += graceBeat.PlaybackDuration;