Add Triangles.Reset()

osu.Game/Graphics/Backgrounds/Triangles.cs

@@ -87,12 +87,9 @@ public Color4 ColourDark
         /// </summary>
         public float Velocity = 1;
 
-        private readonly Random stableRandom;
-
-        private float nextRandom() => (float)(stableRandom?.NextDouble() ?? RNG.NextSingle());
-
         private readonly SortedList<TriangleParticle> parts = new SortedList<TriangleParticle>(Comparer<TriangleParticle>.Default);
 
+        private Random stableRandom;
         private IShader shader;
         private readonly Texture texture;
 
@@ -173,7 +170,20 @@ protected override void Update()
             }
         }
 
-        protected int AimCount;
+        /// <summary>
+        /// Clears and re-initialises triangles according to a given seed.
+        /// </summary>
+        /// <param name="seed">An optional seed to stabilise random positions / attributes. Note that this does not guarantee stable playback when seeking in time.</param>
+        public void Reset(int? seed = null)
+        {
+            if (seed != null)
+                stableRandom = new Random(seed.Value);
+
+            parts.Clear();
+            addTriangles(true);
+        }
+
+        protected int AimCount { get; private set; }
 
         private void addTriangles(bool randomY)
         {
@@ -227,6 +237,8 @@ private void updateColours()
             }
         }
 
+        private float nextRandom() => (float)(stableRandom?.NextDouble() ?? RNG.NextSingle());
+
         protected override DrawNode CreateDrawNode() => new TrianglesDrawNode(this);
 
         private class TrianglesDrawNode : DrawNode