From 622c90daf7f5a0d96b8f13f7d9079720df6cd625 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Mon, 28 Nov 2016 16:52:57 +0900
Subject: [PATCH] Add basic snaking.

---
 .../Objects/Drawables/DrawableSlider.cs       | 33 +++++++++++++++----
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/osu.Game.Mode.Osu/Objects/Drawables/DrawableSlider.cs b/osu.Game.Mode.Osu/Objects/Drawables/DrawableSlider.cs
index b311e0b15f..13401eb6d3 100644
--- a/osu.Game.Mode.Osu/Objects/Drawables/DrawableSlider.cs
+++ b/osu.Game.Mode.Osu/Objects/Drawables/DrawableSlider.cs
@@ -1,4 +1,5 @@
-using osu.Framework.Graphics;
+using System.Collections.Generic;
+using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Game.Modes.Objects.Drawables;
 using osu.Game.Modes.Osu.Objects.Drawables.Pieces;
@@ -60,15 +61,14 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
         {
             base.LoadComplete();
 
-            for (int i = 0; i < slider.Curve.Length; i += 10)
-                path.Positions.Add(slider.Curve.PositionAt(i / slider.Curve.Length));
-
             path.PathWidth = startCircle.DrawWidth / 4;
 
             //force application of the state that was set before we loaded.
             UpdateState(State);
         }
 
+        double snakeDrawn = 0;
+
         protected override void Update()
         {
             base.Update();
@@ -83,9 +83,30 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
                 if (currentRepeat % 2 == 1)
                     t = 1 - t;
             }
-                
-            ball.Position = slider.Curve.PositionAt(t);
 
+            double snake = MathHelper.Clamp((Time.Current - slider.StartTime + 450) / 200, 0, 1);
+            if (snake != snakeDrawn)
+            {
+                if (snake < snakeDrawn)
+                {
+                    //if we have gone backwards, just clear the path for now.
+                    snakeDrawn = 0;
+                    path.Positions.Clear();
+                }
+
+                const double segment_size = 10;
+
+                while (snakeDrawn < snake)
+                {
+                    snakeDrawn += segment_size;
+                    path.Positions.Add(slider.Curve.PositionAt(snake));
+                }
+
+                snakeDrawn = snake;
+                path.Positions.Add(slider.Curve.PositionAt(snake));
+            }
+
+            ball.Position = slider.Curve.PositionAt(t);
         }
 
         protected override void UpdateState(ArmedState state)