From 949e17cc0e8f4666d87b9be541b5c31b3e5686a4 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Tue, 12 May 2020 15:23:47 +0900
Subject: [PATCH] Rework scroller to support backwards playback

---
 .../Skinning/TestSceneTaikoScroller.cs        | 20 ++++++-
 .../Skinning/LegacyTaikoScroller.cs           | 52 +++++++++++--------
 .../UI/DrawableTaikoRuleset.cs                |  2 +-
 3 files changed, 50 insertions(+), 24 deletions(-)

diff --git a/osu.Game.Rulesets.Taiko.Tests/Skinning/TestSceneTaikoScroller.cs b/osu.Game.Rulesets.Taiko.Tests/Skinning/TestSceneTaikoScroller.cs
index e26f410b71..9a2ada7f72 100644
--- a/osu.Game.Rulesets.Taiko.Tests/Skinning/TestSceneTaikoScroller.cs
+++ b/osu.Game.Rulesets.Taiko.Tests/Skinning/TestSceneTaikoScroller.cs
@@ -3,6 +3,7 @@
 
 using osu.Framework.Extensions.IEnumerableExtensions;
 using osu.Framework.Testing;
+using osu.Framework.Timing;
 using osu.Game.Rulesets.Judgements;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.Taiko.Skinning;
@@ -12,11 +13,28 @@ namespace osu.Game.Rulesets.Taiko.Tests.Skinning
 {
     public class TestSceneTaikoScroller : TaikoSkinnableTestScene
     {
+        private readonly ManualClock clock = new ManualClock();
+
+        private bool reversed;
+
         public TestSceneTaikoScroller()
         {
-            AddStep("Load scroller", () => SetContents(() => new SkinnableDrawable(new TaikoSkinComponent(TaikoSkinComponents.TaikoScroller), _ => Empty())));
+            AddStep("Load scroller", () => SetContents(() =>
+                new SkinnableDrawable(new TaikoSkinComponent(TaikoSkinComponents.TaikoScroller), _ => Empty())
+                {
+                    Clock = new FramedClock(clock)
+                }));
             AddToggleStep("Toggle passing", passing => this.ChildrenOfType<LegacyTaikoScroller>().ForEach(s => s.LastResult.Value =
                 new JudgementResult(null, new Judgement()) { Type = passing ? HitResult.Perfect : HitResult.Miss }));
+
+            AddToggleStep("toggle playback direction", reversed => this.reversed = reversed);
+        }
+
+        protected override void Update()
+        {
+            base.Update();
+
+            clock.CurrentTime += (reversed ? -1 : 1) * Clock.ElapsedFrameTime;
         }
     }
 }
diff --git a/osu.Game.Rulesets.Taiko/Skinning/LegacyTaikoScroller.cs b/osu.Game.Rulesets.Taiko/Skinning/LegacyTaikoScroller.cs
index 4cf1af3b8f..b3a325ea68 100644
--- a/osu.Game.Rulesets.Taiko/Skinning/LegacyTaikoScroller.cs
+++ b/osu.Game.Rulesets.Taiko/Skinning/LegacyTaikoScroller.cs
@@ -17,9 +17,6 @@ namespace osu.Game.Rulesets.Taiko.Skinning
 {
     public class LegacyTaikoScroller : CompositeDrawable
     {
-        [Resolved(canBeNull: true)]
-        private GameplayClock gameplayClock { get; set; }
-
         public LegacyTaikoScroller()
         {
             RelativeSizeAxes = Axes.Both;
@@ -59,31 +56,42 @@ namespace osu.Game.Rulesets.Taiko.Skinning
         {
             base.Update();
 
-            while (true)
+            bool wideEnough() =>
+                InternalChildren.Any()
+                && InternalChildren.First().ScreenSpaceDrawQuad.Width * InternalChildren.Count >= ScreenSpaceDrawQuad.Width * 2;
+
+            // store X before checking wide enough so if we perform layout there is no positional discrepancy.
+            float currentX = (InternalChildren?.FirstOrDefault()?.X ?? 0) - (float)Clock.ElapsedFrameTime * 0.1f;
+
+            // ensure we have enough sprites
+            if (!wideEnough())
             {
-                float? additiveX = null;
+                ClearInternal();
 
-                foreach (var sprite in InternalChildren)
-                {
-                    // add the x coordinates and perform re-layout on all sprites as spacing may change with gameplay scale.
-                    sprite.X = additiveX ??= sprite.X - (float)(gameplayClock ?? Clock).ElapsedFrameTime * 0.1f;
+                while (!wideEnough())
+                    AddInternal(new ScrollerSprite { Passing = passing });
+            }
 
-                    additiveX += sprite.DrawWidth - 1;
+            var first = InternalChildren.First();
+            var last = InternalChildren.Last();
 
-                    if (sprite.X + sprite.DrawWidth < 0)
-                        sprite.Expire();
-                }
+            foreach (var sprite in InternalChildren)
+            {
+                // add the x coordinates and perform re-layout on all sprites as spacing may change with gameplay scale.
+                sprite.X = currentX;
+                currentX += sprite.DrawWidth - 1;
+            }
 
-                var last = InternalChildren.LastOrDefault();
+            if (first.ScreenSpaceDrawQuad.TopLeft.X >= ScreenSpaceDrawQuad.TopLeft.X)
+            {
+                foreach (var internalChild in InternalChildren)
+                    internalChild.X -= first.DrawWidth;
+            }
 
-                // only break from this loop once we have saturated horizontal space completely.
-                if (last != null && last.ScreenSpaceDrawQuad.TopRight.X >= ScreenSpaceDrawQuad.TopRight.X)
-                    break;
-
-                AddInternal(new ScrollerSprite
-                {
-                    Passing = passing
-                });
+            if (last.ScreenSpaceDrawQuad.TopRight.X <= ScreenSpaceDrawQuad.TopRight.X)
+            {
+                foreach (var internalChild in InternalChildren)
+                    internalChild.X += first.DrawWidth;
             }
         }
 
diff --git a/osu.Game.Rulesets.Taiko/UI/DrawableTaikoRuleset.cs b/osu.Game.Rulesets.Taiko/UI/DrawableTaikoRuleset.cs
index c0a6c4582c..21d595a97a 100644
--- a/osu.Game.Rulesets.Taiko/UI/DrawableTaikoRuleset.cs
+++ b/osu.Game.Rulesets.Taiko/UI/DrawableTaikoRuleset.cs
@@ -42,7 +42,7 @@ namespace osu.Game.Rulesets.Taiko.UI
         {
             new BarLineGenerator<BarLine>(Beatmap).BarLines.ForEach(bar => Playfield.Add(bar.Major ? new DrawableBarLineMajor(bar) : new DrawableBarLine(bar)));
 
-            AddInternal(scroller = new SkinnableDrawable(new TaikoSkinComponent(TaikoSkinComponents.TaikoScroller), _ => Empty())
+            FrameStableComponents.Add(scroller = new SkinnableDrawable(new TaikoSkinComponent(TaikoSkinComponents.TaikoScroller), _ => Empty())
             {
                 RelativeSizeAxes = Axes.X,
                 Depth = float.MaxValue