From 56922b66be39193d207e1bcf2871ed02ff0e1171 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 6 Mar 2017 11:11:29 +0900
Subject: [PATCH] Refactor sliders to have more central position/progress
 calculations.

---
 .../Objects/Drawables/DrawableSlider.cs       |  7 ++---
 osu.Game.Modes.Osu/Objects/Slider.cs          | 27 ++++++++++++++++++-
 osu.Game.Modes.Osu/Objects/SliderCurve.cs     |  6 ++---
 3 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/osu.Game.Modes.Osu/Objects/Drawables/DrawableSlider.cs b/osu.Game.Modes.Osu/Objects/Drawables/DrawableSlider.cs
index 907ce8da63..a3e78ed422 100644
--- a/osu.Game.Modes.Osu/Objects/Drawables/DrawableSlider.cs
+++ b/osu.Game.Modes.Osu/Objects/Drawables/DrawableSlider.cs
@@ -102,8 +102,8 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
 
             double progress = MathHelper.Clamp((Time.Current - slider.StartTime) / slider.Duration, 0, 1);
 
-            int repeat = (int)(progress * slider.RepeatCount);
-            progress = (progress * slider.RepeatCount) % 1;
+            int repeat = slider.RepeatAt(progress);
+            progress = slider.CurveProgressAt(progress);
 
             if (repeat > currentRepeat)
             {
@@ -112,9 +112,6 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
                 currentRepeat = repeat;
             }
 
-            if (repeat % 2 == 1)
-                progress = 1 - progress;
-
             bouncer2.Position = slider.Curve.PositionAt(body.SnakedEnd ?? 0);
 
             //todo: we probably want to reconsider this before adding scoring, but it looks and feels nice.
diff --git a/osu.Game.Modes.Osu/Objects/Slider.cs b/osu.Game.Modes.Osu/Objects/Slider.cs
index 5f6c50fd72..88abb68d0a 100644
--- a/osu.Game.Modes.Osu/Objects/Slider.cs
+++ b/osu.Game.Modes.Osu/Objects/Slider.cs
@@ -14,7 +14,32 @@ namespace osu.Game.Modes.Osu.Objects
     {
         public override double EndTime => StartTime + RepeatCount * Curve.Length / Velocity;
 
-        public override Vector2 EndPosition => RepeatCount % 2 == 0 ? Position : Curve.PositionAt(1);
+        public override Vector2 EndPosition => PositionAt(1);
+
+        /// <summary>
+        /// Computes the position on the slider at a given progress that ranges from 0 (beginning of the slider)
+        /// to 1 (end of the slider). This includes repeat logic.
+        /// </summary>
+        /// <param name="progress">Ranges from 0 (beginning of the slider) to 1 (end of the slider).</param>
+        /// <returns></returns>
+        public Vector2 PositionAt(double progress) => Curve.PositionAt(CurveProgressAt(progress));
+
+        /// <summary>
+        /// Find the current progress along the curve, accounting for repeat logic.
+        /// </summary>
+        public double CurveProgressAt(double progress)
+        {
+            var p = progress * RepeatCount % 1;
+            if (RepeatAt(progress) % 2 == 1)
+                p = 1 - p;
+            return p;
+        }
+
+        /// <summary>
+        /// Determine which repeat of the slider we are on at a given progress.
+        /// Range is 0..RepeatCount where 0 is the first run.
+        /// </summary>
+        public int RepeatAt(double progress) => (int)(progress * RepeatCount);
 
         private int stackHeight;
         public override int StackHeight
diff --git a/osu.Game.Modes.Osu/Objects/SliderCurve.cs b/osu.Game.Modes.Osu/Objects/SliderCurve.cs
index 3b52a41b8c..e37da355c0 100644
--- a/osu.Game.Modes.Osu/Objects/SliderCurve.cs
+++ b/osu.Game.Modes.Osu/Objects/SliderCurve.cs
@@ -186,10 +186,10 @@ namespace osu.Game.Modes.Osu.Objects
         }
 
         /// <summary>
-        /// Computes the position on the slider at a given progress that ranges from 0 (beginning of the slider)
-        /// to 1 (end of the slider).
+        /// Computes the position on the slider at a given progress that ranges from 0 (beginning of the curve)
+        /// to 1 (end of the curve).
         /// </summary>
-        /// <param name="progress">Ranges from 0 (beginning of the slider) to 1 (end of the slider).</param>
+        /// <param name="progress">Ranges from 0 (beginning of the curve) to 1 (end of the curve).</param>
         /// <returns></returns>
         public Vector2 PositionAt(double progress)
         {