Treat non-DrawableHitCircle's similar to OsuModHidden

osu.Game.Rulesets.Osu/Mods/OsuModTraceable.cs

@@ -1,11 +1,14 @@
 // Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using System;
 using System.Collections.Generic;
 using osu.Game.Graphics;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Objects.Drawables;
 using osu.Game.Rulesets.Osu.Objects.Drawables;
+using osu.Framework.Graphics;
+using osu.Game.Rulesets.Objects.Types;
 
 namespace osu.Game.Rulesets.Osu.Mods
 {
@@ -21,11 +24,61 @@ internal class OsuModTraceable : Mod, IApplicableToDrawableHitObjects
         public void ApplyToDrawableHitObjects(IEnumerable<DrawableHitObject> drawables)
         {
             foreach (var drawable in drawables)
+                drawable.ApplyCustomUpdateState += ApplyTraceableState;
+        }
+
+        /* Similar to ApplyHiddenState, only different if drawable is DrawableHitCircle.
+         * If we'd use ApplyHiddenState instead but only on non-DrawableHitCircle's, then 
+         * the nested object HeadCircle of DrawableSlider would still use ApplyHiddenState,
+         * thus treating the DrawableHitCircle with the hidden mod instead of the traceable mod.
+         */
+        protected void ApplyTraceableState(DrawableHitObject drawable, ArmedState state)
+        {
+            if (!(drawable is DrawableOsuHitObject d))
+                return;
+
+            var h = d.HitObject;
+
+            var fadeOutStartTime = h.StartTime - h.TimePreempt + h.TimeFadeIn;
+
+            // new duration from completed fade in to end (before fading out)
+            var longFadeDuration = ((h as IHasEndTime)?.EndTime ?? h.StartTime) - fadeOutStartTime;
+
+            switch (drawable)
             {
-                if (drawable is DrawableHitCircle c)
-                    c.HideButApproachCircle();
-                if (drawable is DrawableSlider s)
-                    s.HeadCircle.HideButApproachCircle();
+                case DrawableHitCircle circle:
+                    // we only want to see the approach circle
+                    using (circle.BeginAbsoluteSequence(h.StartTime - h.TimePreempt, true))
+                        circle.HideButApproachCircle();
+
+                    // approach circle fades out quickly at StartTime
+                    using (drawable.BeginAbsoluteSequence(h.StartTime, true))
+                        circle.ApproachCircle.FadeOut(50);
+
+                    break;
+                case DrawableSlider slider:
+                    using (slider.BeginAbsoluteSequence(fadeOutStartTime, true))
+                        slider.Body.FadeOut(longFadeDuration, Easing.Out);
+
+                    break;
+                case DrawableSliderTick sliderTick:
+                    // slider ticks fade out over up to one second
+                    var tickFadeOutDuration = Math.Min(sliderTick.HitObject.TimePreempt - DrawableSliderTick.ANIM_DURATION, 1000);
+
+                    using (sliderTick.BeginAbsoluteSequence(sliderTick.HitObject.StartTime - tickFadeOutDuration, true))
+                        sliderTick.FadeOut(tickFadeOutDuration);
+
+                    break;
+                case DrawableSpinner spinner:
+                    // hide elements we don't care about.
+                    spinner.Disc.Hide();
+                    spinner.Ticks.Hide();
+                    spinner.Background.Hide();
+
+                    using (spinner.BeginAbsoluteSequence(fadeOutStartTime + longFadeDuration, true))
+                        spinner.FadeOut(h.TimePreempt);
+
+                    break;
             }
         }
     }

osu.Game.Rulesets.Osu/Objects/Drawables/DrawableHitCircle.cs

@@ -81,6 +81,8 @@ public void HideButApproachCircle()
             circle.Hide();
             circle.AlwaysPresent = true;
             ring.Hide();
+            flash.Hide();
+            explode.Hide();
             number.Hide();
             glow.Hide();
         }