Make Triangles more flexible and more random.

osu.Game/Graphics/Backgrounds/Triangles.cs

@@ -0,0 +1,63 @@
+//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
+//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Linq;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Sprites;
+using osu.Framework.Graphics.Textures;
+using osu.Framework.MathUtils;
+using OpenTK;
+
+namespace osu.Game.Graphics.Backgrounds
+{
+    public class Triangles : Container
+    {
+        private Texture triangle;
+
+        public Triangles()
+        {
+            Masking = true;
+            Alpha = 0.3f;
+        }
+
+        [BackgroundDependencyLoader]
+        private void load(TextureStore textures)
+        {
+            triangle = textures.Get(@"Play/osu/triangle@2x");
+        }
+
+        private int aimTriangleCount => (int)((DrawWidth * DrawHeight) / 800);
+
+        protected override void Update()
+        {
+            base.Update();
+
+            foreach (Drawable d in Children)
+            {
+                d.Position -= new Vector2(0, (float)(d.Scale.X * (Time.Elapsed / 880)));
+                if (d.DrawPosition.Y + d.DrawSize.Y * d.Scale.Y < 0)
+                    d.Expire();
+            }
+
+            bool useRandomX = Children.Count() < aimTriangleCount / 2;
+            while (Children.Count() < aimTriangleCount)
+                addTriangle(useRandomX);
+
+        }
+
+        private void addTriangle(bool randomX)
+        {
+            Add(new Sprite
+            {
+                Texture = triangle,
+                Origin = Anchor.TopCentre,
+                RelativePositionAxes = Axes.Both,
+                Position = new Vector2(RNG.NextSingle(), randomX ? RNG.NextSingle() : 1),
+                Scale = new Vector2(RNG.NextSingle() * 0.4f + 0.2f),
+                Alpha = RNG.NextSingle()
+            });
+        }
+    }
+}