From 13f16077d452333ac0e62948fa5fa886f0fdab7b Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Thu, 1 Feb 2018 20:04:41 +0900
Subject: [PATCH] Implement Catmull-Rom curve approximator

---
 osu.Game.Rulesets.Osu/Tests/TestCaseSlider.cs | 34 +++++++++
 .../Rulesets/Objects/CatmullApproximator.cs   | 70 +++++++++++++++++++
 osu.Game/Rulesets/Objects/SliderCurve.cs      |  2 +
 osu.Game/osu.Game.csproj                      |  1 +
 4 files changed, 107 insertions(+)
 create mode 100644 osu.Game/Rulesets/Objects/CatmullApproximator.cs

diff --git a/osu.Game.Rulesets.Osu/Tests/TestCaseSlider.cs b/osu.Game.Rulesets.Osu/Tests/TestCaseSlider.cs
index b8e04de880..ea3ad88cdd 100644
--- a/osu.Game.Rulesets.Osu/Tests/TestCaseSlider.cs
+++ b/osu.Game.Rulesets.Osu/Tests/TestCaseSlider.cs
@@ -19,6 +19,7 @@ using System.Linq;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Rulesets.Judgements;
 using osu.Game.Rulesets.Objects.Drawables;
+using osu.Game.Rulesets.Objects.Types;
 using osu.Game.Rulesets.Osu.Objects.Drawables.Pieces;
 
 namespace osu.Game.Rulesets.Osu.Tests
@@ -71,6 +72,10 @@ namespace osu.Game.Rulesets.Osu.Tests
             AddStep("Fast Short Slider 6 Repeats", () => testShortHighSpeed(6));
 
             AddStep("Perfect Curve", testCurve);
+
+            AddStep("Catmull", () => testCatmull());
+            AddStep("Catmull 1 Repeat", () => testCatmull(1));
+
             // TODO more curve types?
         }
 
@@ -131,6 +136,35 @@ namespace osu.Game.Rulesets.Osu.Tests
             addSlider(slider, 2, 3);
         }
 
+        private void testCatmull(int repeats = 0) => createCatmull(repeats);
+
+        private void createCatmull(int repeats = 0)
+        {
+            var repeatSamples = new List<List<SampleInfo>>();
+            for (int i = 0; i < repeats; i++)
+                repeatSamples.Add(new List<SampleInfo>());
+
+            var slider = new Slider
+            {
+                StartTime = Time.Current + 1000,
+                Position = new Vector2(-100, 0),
+                ComboColour = Color4.LightSeaGreen,
+                CurveType = CurveType.Catmull,
+                ControlPoints = new List<Vector2>
+                {
+                    new Vector2(-100, 0),
+                    new Vector2(-50, -50),
+                    new Vector2(50, 50),
+                    new Vector2(100, 0)
+                },
+                Distance = 300,
+                RepeatCount = repeats,
+                RepeatSamples = repeatSamples
+            };
+
+            addSlider(slider, 3, 1);
+        }
+
         private void addSlider(Slider slider, float circleSize, double speedMultiplier)
         {
             var cpi = new ControlPointInfo();
diff --git a/osu.Game/Rulesets/Objects/CatmullApproximator.cs b/osu.Game/Rulesets/Objects/CatmullApproximator.cs
new file mode 100644
index 0000000000..364b4e995a
--- /dev/null
+++ b/osu.Game/Rulesets/Objects/CatmullApproximator.cs
@@ -0,0 +1,70 @@
+// 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.Objects
+{
+    public class CatmullApproximator
+    {
+        /// <summary>
+        /// The amount of pieces to calculate for each controlpoint quadruplet.
+        /// </summary>
+        private const int detail = 50;
+
+        private readonly List<Vector2> controlPoints;
+
+        public CatmullApproximator(List<Vector2> controlPoints)
+        {
+            this.controlPoints = controlPoints;
+        }
+
+
+        /// <summary>
+        /// Creates a piecewise-linear approximation of a Catmull-Rom spline.
+        /// </summary>
+        /// <returns>A list of vectors representing the piecewise-linear approximation.</returns>
+        public List<Vector2> CreateCatmull()
+        {
+            var result = new List<Vector2>();
+
+            for (int i = 0; i < controlPoints.Count - 1; i++)
+            {
+                var v1 = i > 0 ? controlPoints[i - 1] : controlPoints[i];
+                var v2 = controlPoints[i];
+                var v3 = i < controlPoints.Count - 1 ? controlPoints[i + 1] : v2 + v2 - v1;
+                var v4 = i < controlPoints.Count - 2 ? controlPoints[i + 2] : v3 + v3 - v2;
+
+                for (int c = 0; c < detail; c++)
+                {
+                    result.Add(findPoint(ref v1, ref v2, ref v3, ref v4, (float)c / detail));
+                    result.Add(findPoint(ref v1, ref v2, ref v3, ref v4, (float)(c + 1) / detail));
+                }
+            }
+
+            return result;
+        }
+
+        /// <summary>
+        /// Finds a point on the spline at the position of a parameter.
+        /// </summary>
+        /// <param name="vec1">The first vector.</param>
+        /// <param name="vec2">The second vector.</param>
+        /// <param name="vec3">The third vector.</param>
+        /// <param name="vec4">The fourth vector.</param>
+        /// <param name="t">The parameter at which to find the point on the spline, in the range [0, 1].</param>
+        /// <returns>The point on the spline at <paramref name="t"/>.</returns>
+        private Vector2 findPoint(ref Vector2 vec1, ref Vector2 vec2, ref Vector2 vec3, ref Vector2 vec4, float t)
+        {
+            float t2 = t * t;
+            float t3 = t * t2;
+
+            Vector2 result;
+            result.X = 0.5f * (2f * vec2.X + (-vec1.X + vec3.X) * t + (2f * vec1.X - 5f * vec2.X + 4f * vec3.X - vec4.X) * t2 + (-vec1.X + 3f * vec2.X - 3f * vec3.X + vec4.X) * t3);
+            result.Y = 0.5f * (2f * vec2.Y + (-vec1.Y + vec3.Y) * t + (2f * vec1.Y - 5f * vec2.Y + 4f * vec3.Y - vec4.Y) * t2 + (-vec1.Y + 3f * vec2.Y - 3f * vec3.Y + vec4.Y) * t3);
+
+            return result;
+        }
+    }
+}
diff --git a/osu.Game/Rulesets/Objects/SliderCurve.cs b/osu.Game/Rulesets/Objects/SliderCurve.cs
index ae79d62ec8..2b16f463df 100644
--- a/osu.Game/Rulesets/Objects/SliderCurve.cs
+++ b/osu.Game/Rulesets/Objects/SliderCurve.cs
@@ -41,6 +41,8 @@ namespace osu.Game.Rulesets.Objects
                         break;
 
                     return subpath;
+                case CurveType.Catmull:
+                    return new CatmullApproximator(subControlPoints).CreateCatmull();
             }
 
             return new BezierApproximator(subControlPoints).CreateBezier();
diff --git a/osu.Game/osu.Game.csproj b/osu.Game/osu.Game.csproj
index 12e2f45d76..4944613828 100644
--- a/osu.Game/osu.Game.csproj
+++ b/osu.Game/osu.Game.csproj
@@ -340,6 +340,7 @@
     <Compile Include="Overlays\Social\SocialPanel.cs" />
     <Compile Include="Rulesets\Mods\IApplicableToDrawableHitObject.cs" />
     <Compile Include="Screens\Play\PlayerSettings\VisualSettings.cs" />
+    <Compile Include="Rulesets\Objects\CatmullApproximator.cs" />
     <Compile Include="Rulesets\UI\HitObjectContainer.cs" />
     <Compile Include="Rulesets\UI\Scrolling\Visualisers\SequentialSpeedChangeVisualiser.cs" />
     <Compile Include="Rulesets\UI\Scrolling\Visualisers\ISpeedChangeVisualiser.cs" />