Fix various inconsistencies and document better

osu.Game/Screens/Play/HUD/ArgonSongProgress.cs

@@ -114,7 +114,6 @@ namespace osu.Game.Screens.Play.HUD
 
         protected override void UpdateProgress(double progress, bool isIntro)
         {
-            bar.CurrentTime = GameplayClock.CurrentTime;
             bar.Progress = isIntro ? 0 : progress;
         }
     }

osu.Game/Screens/Play/HUD/ArgonSongProgressBar.cs

@@ -48,6 +48,7 @@ namespace osu.Game.Screens.Play.HUD
                     RelativeSizeAxes = Axes.Both,
                     Alpha = 0,
                     Colour = OsuColour.Gray(0.2f),
+                    Depth = float.MaxValue,
                 },
                 audioBar = new RoundedBar
                 {
@@ -102,14 +103,14 @@ namespace osu.Game.Screens.Play.HUD
             base.Update();
 
             playfieldBar.Length = (float)Interpolation.Lerp(playfieldBar.Length, Progress, Math.Clamp(Time.Elapsed / 40, 0, 1));
-            audioBar.Length = (float)Interpolation.Lerp(audioBar.Length, NormalizedValue, Math.Clamp(Time.Elapsed / 40, 0, 1));
+            audioBar.Length = (float)Interpolation.Lerp(audioBar.Length, AudioProgress, Math.Clamp(Time.Elapsed / 40, 0, 1));
 
-            if (trackTime > CurrentTime)
+            if (trackTime > AudioTime)
                 ChangeInternalChildDepth(audioBar, -1);
             else
-                ChangeInternalChildDepth(audioBar, 0);
+                ChangeInternalChildDepth(audioBar, 1);
 
-            float timeDelta = (float)Math.Abs(CurrentTime - trackTime);
+            float timeDelta = (float)Math.Abs(AudioTime - trackTime);
 
             const float colour_transition_threshold = 20000;
 

osu.Game/Screens/Play/HUD/DefaultSongProgress.cs

@@ -98,7 +98,6 @@ namespace osu.Game.Screens.Play.HUD
 
         protected override void UpdateProgress(double progress, bool isIntro)
         {
-            bar.CurrentTime = GameplayClock.CurrentTime;
             graph.Progress = isIntro ? 0 : (int)(graph.ColumnCount * progress);
         }
 

osu.Game/Screens/Play/HUD/DefaultSongProgressBar.cs

@@ -98,7 +98,7 @@ namespace osu.Game.Screens.Play.HUD
             base.Update();
 
             handleBase.Height = Height - handleContainer.Height;
-            float newX = (float)Interpolation.Lerp(handleBase.X, NormalizedValue * DrawWidth, Math.Clamp(Time.Elapsed / 40, 0, 1));
+            float newX = (float)Interpolation.Lerp(handleBase.X, AudioProgress * DrawWidth, Math.Clamp(Time.Elapsed / 40, 0, 1));
 
             fill.Width = newX;
             handleBase.X = newX;

osu.Game/Screens/Play/HUD/SongProgress.cs

@@ -71,7 +71,13 @@ namespace osu.Game.Screens.Play.HUD
 
         protected double LastHitTime { get; private set; }
 
+        /// <summary>
+        /// Called every update frame with current progress information.
+        /// </summary>
+        /// <param name="progress">Current (visual) progress through the beatmap (0..1).</param>
+        /// <param name="isIntro">If <c>true</c>, progress is (0..1) through the intro.</param>
         protected abstract void UpdateProgress(double progress, bool isIntro);
+
         protected virtual void UpdateObjects(IEnumerable<HitObject> objects) { }
 
         [BackgroundDependencyLoader]

osu.Game/Screens/Play/HUD/SongProgressBar.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Input.Events;
@@ -12,6 +13,20 @@ namespace osu.Game.Screens.Play.HUD
 {
     public abstract partial class SongProgressBar : CompositeDrawable
     {
+        /// <summary>
+        /// The current seek position of the audio, on a (0..1) range.
+        /// This is generally the seek target, which will eventually match the gameplay clock when it catches up.
+        /// </summary>
+        protected double AudioProgress => length == 0 ? 1 : AudioTime / length;
+
+        /// <summary>
+        /// The current (non-frame-stable) audio time.
+        /// </summary>
+        protected double AudioTime => Math.Clamp(GameplayClock.CurrentTime - StartTime, 0.0, length);
+
+        [Resolved]
+        protected IGameplayClock GameplayClock { get; private set; } = null!;
+
         /// <summary>
         /// Action which is invoked when a seek is requested, with the proposed millisecond value for the seek operation.
         /// </summary>
@@ -32,12 +47,8 @@ namespace osu.Game.Screens.Play.HUD
 
         public double EndTime { get; set; } = 1.0;
 
-        public double CurrentTime { get; set; }
-
         private double length => EndTime - StartTime;
 
-        protected double NormalizedValue => length == 0 ? 1 : Math.Clamp(CurrentTime - StartTime, 0.0, length) / length;
-
         private bool handleClick;
 
         protected override bool OnMouseDown(MouseDownEvent e)