Separate slider body to bypass snaking logic

The snaking logic contains a lot of caching/optimisations and offsetting of the path which is tedious to re-compute when the path changes.

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

@@ -23,7 +23,7 @@ namespace osu.Game.Rulesets.Osu.Objects.Drawables
         public readonly DrawableHitCircle HeadCircle;
         public readonly DrawableSliderTail TailCircle;
 
-        public readonly SliderBody Body;
+        public readonly SnakingSliderBody Body;
         public readonly SliderBall Ball;
 
         public DrawableSlider(Slider s)
@@ -38,7 +38,7 @@ namespace osu.Game.Rulesets.Osu.Objects.Drawables
 
             InternalChildren = new Drawable[]
             {
-                Body = new SliderBody(s)
+                Body = new SnakingSliderBody(s)
                 {
                     PathWidth = s.Scale * 64,
                 },

osu.Game.Rulesets.Osu/Objects/Drawables/Pieces/ManualSliderBody.cs

@@ -0,0 +1,20 @@
+// 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.Collections.Generic;
+using OpenTK;
+
+namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
+{
+    /// <summary>
+    /// A <see cref="SliderBody"/> with the ability to set the drawn vertices manually.
+    /// </summary>
+    public class ManualSliderBody : SliderBody
+    {
+        public new void SetVertices(IReadOnlyList<Vector2> vertices)
+        {
+            base.SetVertices(vertices);
+            Size = Path.Size;
+        }
+    }
+}

osu.Game.Rulesets.Osu/Objects/Drawables/Pieces/SliderBody.cs

@@ -1,24 +1,22 @@
-// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// 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.Framework.Allocation;
-using osu.Framework.Configuration;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Lines;
-using OpenTK.Graphics.ES30;
-using OpenTK.Graphics;
 using osu.Framework.Graphics.Primitives;
-using osu.Game.Rulesets.Objects.Types;
 using OpenTK;
+using OpenTK.Graphics;
+using OpenTK.Graphics.ES30;
 
 namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
 {
-    public class SliderBody : Container, ISliderProgress
+    public abstract class SliderBody : CompositeDrawable
     {
         private readonly SliderPath path;
+        protected Path Path => path;
+
         private readonly BufferedContainer container;
 
         public float PathWidth
@@ -30,15 +28,7 @@ namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
         /// <summary>
         /// Offset in absolute coordinates from the start of the curve.
         /// </summary>
-        public Vector2 PathOffset { get; private set; }
+        public virtual Vector2 PathOffset => path.PositionInBoundingBox(path.Vertices[0]);
-
-        public readonly List<Vector2> CurrentCurve = new List<Vector2>();
-
-        public readonly Bindable<bool> SnakingIn = new Bindable<bool>();
-        public readonly Bindable<bool> SnakingOut = new Bindable<bool>();
-
-        public double? SnakedStart { get; private set; }
-        public double? SnakedEnd { get; private set; }
 
         /// <summary>
         /// Used to colour the path.
@@ -74,28 +64,13 @@ namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
 
         public Quad PathDrawQuad => container.ScreenSpaceDrawQuad;
 
-        private Vector2 topLeftOffset;
+        protected SliderBody()
-
-        private readonly Slider slider;
-
-        public SliderBody(Slider s)
         {
-            slider = s;
+            InternalChild = container = new BufferedContainer
-
-            Children = new Drawable[]
             {
-                container = new BufferedContainer
+                RelativeSizeAxes = Axes.Both,
-                {
+                CacheDrawnFrameBuffer = true,
-                    RelativeSizeAxes = Axes.Both,
+                Child = path = new SliderPath { Blending = BlendingMode.None }
-                    CacheDrawnFrameBuffer = true,
-                    Children = new Drawable[]
-                    {
-                        path = new SliderPath
-                        {
-                            Blending = BlendingMode.None,
-                        },
-                    }
-                },
             };
 
             container.Attach(RenderbufferInternalFormat.DepthComponent16);
@@ -103,80 +78,14 @@ namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
 
         public override bool ReceivePositionalInputAt(Vector2 screenSpacePos) => path.ReceivePositionalInputAt(screenSpacePos);
 
-        public void SetRange(double p0, double p1)
+        /// <summary>
+        /// Sets the vertices of the path which should be drawn by this <see cref="SliderBody"/>.
+        /// </summary>
+        /// <param name="vertices">The vertices</param>
+        protected void SetVertices(IReadOnlyList<Vector2> vertices)
         {
-            if (p0 > p1)
+            path.Vertices = vertices;
-                MathHelper.Swap(ref p0, ref p1);
+            container.ForceRedraw();
-
-            if (updateSnaking(p0, p1))
-            {
-                // The path is generated such that its size encloses it. This change of size causes the path
-                // to move around while snaking, so we need to offset it to make sure it maintains the
-                // same position as when it is fully snaked.
-                var newTopLeftOffset = path.PositionInBoundingBox(Vector2.Zero);
-                path.Position = topLeftOffset - newTopLeftOffset;
-
-                container.ForceRedraw();
-            }
-        }
-
-        [BackgroundDependencyLoader]
-        private void load()
-        {
-            computeSize();
-        }
-
-        private void computeSize()
-        {
-            // Generate the entire curve
-            slider.Curve.GetPathToProgress(CurrentCurve, 0, 1);
-            foreach (Vector2 p in CurrentCurve)
-                path.AddVertex(p);
-
-            Size = path.Size;
-
-            topLeftOffset = path.PositionInBoundingBox(Vector2.Zero);
-            PathOffset = path.PositionInBoundingBox(CurrentCurve[0]);
-        }
-
-        private bool updateSnaking(double p0, double p1)
-        {
-            if (SnakedStart == p0 && SnakedEnd == p1) return false;
-
-            SnakedStart = p0;
-            SnakedEnd = p1;
-
-            slider.Curve.GetPathToProgress(CurrentCurve, p0, p1);
-
-            path.ClearVertices();
-            foreach (Vector2 p in CurrentCurve)
-                path.AddVertex(p);
-
-            return true;
-        }
-
-        public void UpdateProgress(double completionProgress)
-        {
-            var span = slider.SpanAt(completionProgress);
-            var spanProgress = slider.ProgressAt(completionProgress);
-
-            double start = 0;
-            double end = SnakingIn ? MathHelper.Clamp((Time.Current - (slider.StartTime - slider.TimePreempt)) / slider.TimeFadeIn, 0, 1) : 1;
-
-            if (span >= slider.SpanCount() - 1)
-            {
-                if (Math.Min(span, slider.SpanCount() - 1) % 2 == 1)
-                {
-                    start = 0;
-                    end = SnakingOut ? spanProgress : 1;
-                }
-                else
-                {
-                    start = SnakingOut ? spanProgress : 0;
-                }
-            }
-
-            SetRange(start, end);
         }
 
         private class SliderPath : SmoothPath

osu.Game.Rulesets.Osu/Objects/Drawables/Pieces/SnakingSliderBody.cs

@@ -0,0 +1,105 @@
+// 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.Framework.Allocation;
+using osu.Framework.Configuration;
+using osu.Game.Rulesets.Objects.Types;
+using OpenTK;
+
+namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
+{
+    /// <summary>
+    /// A <see cref="SliderBody"/> which changes its curve depending on the snaking progress.
+    /// </summary>
+    public class SnakingSliderBody : SliderBody, ISliderProgress
+    {
+        public readonly List<Vector2> CurrentCurve = new List<Vector2>();
+
+        public readonly Bindable<bool> SnakingIn = new Bindable<bool>();
+        public readonly Bindable<bool> SnakingOut = new Bindable<bool>();
+
+        public double? SnakedStart { get; private set; }
+        public double? SnakedEnd { get; private set; }
+
+        public override Vector2 PathOffset => snakedPathOffset;
+
+        /// <summary>
+        /// The top-left position of the path when fully snaked.
+        /// </summary>
+        private Vector2 snakedPosition;
+
+        /// <summary>
+        /// The offset of the path from <see cref="snakedPosition"/> when fully snaked.
+        /// </summary>
+        private Vector2 snakedPathOffset;
+
+        private readonly Slider slider;
+
+        public SnakingSliderBody(Slider slider)
+        {
+            this.slider = slider;
+        }
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            // Generate the entire curve
+            slider.Curve.GetPathToProgress(CurrentCurve, 0, 1);
+            SetVertices(CurrentCurve);
+
+            // The body is sized to the full path size to avoid excessive autosize computations
+            Size = Path.Size;
+
+            snakedPosition = Path.PositionInBoundingBox(Vector2.Zero);
+            snakedPathOffset = Path.PositionInBoundingBox(Path.Vertices[0]);
+        }
+
+        public void UpdateProgress(double completionProgress)
+        {
+            var span = slider.SpanAt(completionProgress);
+            var spanProgress = slider.ProgressAt(completionProgress);
+
+            double start = 0;
+            double end = SnakingIn ? MathHelper.Clamp((Time.Current - (slider.StartTime - slider.TimePreempt)) / slider.TimeFadeIn, 0, 1) : 1;
+
+            if (span >= slider.SpanCount() - 1)
+            {
+                if (Math.Min(span, slider.SpanCount() - 1) % 2 == 1)
+                {
+                    start = 0;
+                    end = SnakingOut ? spanProgress : 1;
+                }
+                else
+                {
+                    start = SnakingOut ? spanProgress : 0;
+                }
+            }
+
+            setRange(start, end);
+        }
+
+        private void setRange(double p0, double p1)
+        {
+            if (p0 > p1)
+                MathHelper.Swap(ref p0, ref p1);
+
+            if (SnakedStart == p0 && SnakedEnd == p1) return;
+
+            SnakedStart = p0;
+            SnakedEnd = p1;
+
+            slider.Curve.GetPathToProgress(CurrentCurve, p0, p1);
+
+            SetVertices(CurrentCurve);
+
+            // The bounding box of the path expands as it snakes, which in turn shifts the position of the path.
+            // Depending on the direction of expansion, it may appear as if the path is expanding towards the position of the slider
+            // rather than expanding out from the position of the slider.
+            // To remove this effect, the path's position is shifted towards its final snaked position
+
+            Path.Position = snakedPosition - Path.PositionInBoundingBox(Vector2.Zero);
+        }
+    }
+}