Restore original IHasCurve implementation

osu.Game/Rulesets/Objects/Legacy/ConvertSlider.cs

@@ -9,7 +9,10 @@
 
 namespace osu.Game.Rulesets.Objects.Legacy
 {
-    internal abstract class ConvertSlider : ConvertHitObject, IHasPathWithRepeats, IHasLegacyLastTickOffset
+    internal abstract class ConvertSlider : ConvertHitObject, IHasPathWithRepeats, IHasLegacyLastTickOffset,
+#pragma warning disable 618
+                                            IHasCurve
+#pragma warning restore 618
     {
         /// <summary>
         /// Scoring distance with a speed-adjusted beat length of 1 second.

osu.Game/Rulesets/Objects/Types/IHasCurve.cs

@@ -0,0 +1,55 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osuTK;
+
+namespace osu.Game.Rulesets.Objects.Types
+{
+    [Obsolete("Use IHasPathWithRepeats instead.")] // can be removed 20201126
+    public interface IHasCurve : IHasDistance, IHasRepeats
+    {
+        /// <summary>
+        /// The curve.
+        /// </summary>
+        SliderPath Path { get; }
+    }
+
+#pragma warning disable 618
+    [Obsolete("Use IHasPathWithRepeats instead.")] // can be removed 20201126
+    public static class HasCurveExtensions
+    {
+        /// <summary>
+        /// Computes the position on the curve relative to how much of the <see cref="HitObject"/> has been completed.
+        /// </summary>
+        /// <param name="obj">The curve.</param>
+        /// <param name="progress">[0, 1] where 0 is the start time of the <see cref="HitObject"/> and 1 is the end time of the <see cref="HitObject"/>.</param>
+        /// <returns>The position on the curve.</returns>
+        public static Vector2 CurvePositionAt(this IHasCurve obj, double progress)
+            => obj.Path.PositionAt(obj.ProgressAt(progress));
+
+        /// <summary>
+        /// Computes the progress along the curve relative to how much of the <see cref="HitObject"/> has been completed.
+        /// </summary>
+        /// <param name="obj">The curve.</param>
+        /// <param name="progress">[0, 1] where 0 is the start time of the <see cref="HitObject"/> and 1 is the end time of the <see cref="HitObject"/>.</param>
+        /// <returns>[0, 1] where 0 is the beginning of the curve and 1 is the end of the curve.</returns>
+        public static double ProgressAt(this IHasCurve obj, double progress)
+        {
+            double p = progress * obj.SpanCount() % 1;
+            if (obj.SpanAt(progress) % 2 == 1)
+                p = 1 - p;
+            return p;
+        }
+
+        /// <summary>
+        /// Determines which span of the curve the progress point is on.
+        /// </summary>
+        /// <param name="obj">The curve.</param>
+        /// <param name="progress">[0, 1] where 0 is the beginning of the curve and 1 is the end of the curve.</param>
+        /// <returns>[0, SpanCount) where 0 is the first run.</returns>
+        public static int SpanAt(this IHasCurve obj, double progress)
+            => (int)(progress * obj.SpanCount());
+    }
+#pragma warning restore 618
+}

osu.Game/Rulesets/Objects/Types/IHasPathWithRepeats.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System;
 using osuTK;
 
 namespace osu.Game.Rulesets.Objects.Types
@@ -9,14 +8,8 @@ namespace osu.Game.Rulesets.Objects.Types
     /// <summary>
     /// A HitObject that has a curve.
     /// </summary>
-#pragma warning disable 618
-    public interface IHasPathWithRepeats : IHasCurve
-#pragma warning restore 618
-    {
-    }
-
-    [Obsolete("Use IHasPathWithRepeats instead.")] // can be removed 20201126
-    public interface IHasCurve : IHasPath, IHasRepeats
+    // ReSharper disable once RedundantExtendsListEntry
+    public interface IHasPathWithRepeats : IHasPath, IHasRepeats
     {
     }