Add abstract implementation of slider path

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

@@ -0,0 +1,70 @@
+// 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 osu.Framework.Graphics.Lines;
+using osuTK.Graphics;
+
+namespace osu.Game.Rulesets.Osu.Objects.Drawables.Pieces
+{
+    public abstract class DrawableSliderPath : SmoothPath
+    {
+        protected const float BORDER_PORTION = 0.128f;
+        protected const float GRADIENT_PORTION = 1 - BORDER_PORTION;
+
+        private const float border_max_size = 8f;
+        private const float border_min_size = 0f;
+
+        private Color4 borderColour = Color4.White;
+
+        public Color4 BorderColour
+        {
+            get => borderColour;
+            set
+            {
+                if (borderColour == value)
+                    return;
+
+                borderColour = value;
+
+                InvalidateTexture();
+            }
+        }
+
+        private Color4 accentColour = Color4.White;
+
+        public Color4 AccentColour
+        {
+            get => accentColour;
+            set
+            {
+                if (accentColour == value)
+                    return;
+
+                accentColour = value;
+
+                InvalidateTexture();
+            }
+        }
+
+        private float borderSize = 1;
+
+        public float BorderSize
+        {
+            get => borderSize;
+            set
+            {
+                if (borderSize == value)
+                    return;
+
+                if (value < border_min_size || value > border_max_size)
+                    return;
+
+                borderSize = value;
+
+                InvalidateTexture();
+            }
+        }
+
+        protected float CalculatedBorderPortion => BorderSize * BORDER_PORTION;
+    }
+}