Avoid Triangles draw node invalidation when nothing is changing

Basically only helps when time is paused. ie in the editor.

osu.Game/Graphics/Backgrounds/Triangles.cs

@@ -127,8 +127,6 @@ namespace osu.Game.Graphics.Backgrounds
         {
             base.Update();
 
-            Invalidate(Invalidation.DrawNode);
-
             if (CreateNewTriangles)
                 addTriangles(false);
 
@@ -138,6 +136,10 @@ namespace osu.Game.Graphics.Backgrounds
                 : 1;
 
             float elapsedSeconds = (float)Time.Elapsed / 1000;
+
+            if (elapsedSeconds == 0)
+                return;
+
             // Since position is relative, the velocity needs to scale inversely with DrawHeight.
             // Since we will later multiply by the scale of individual triangles we normalize by
             // dividing by triangleScale.
@@ -157,6 +159,8 @@ namespace osu.Game.Graphics.Backgrounds
                 if (bottomPos < 0)
                     parts.RemoveAt(i);
             }
+
+            Invalidate(Invalidation.DrawNode);
         }
 
         /// <summary>
@@ -183,8 +187,13 @@ namespace osu.Game.Graphics.Backgrounds
 
             int currentCount = parts.Count;
 
+            if (AimCount - currentCount == 0)
+                return;
+
             for (int i = 0; i < AimCount - currentCount; i++)
                 parts.Add(createTriangle(randomY));
+
+            Invalidate(Invalidation.DrawNode);
         }
 
         private TriangleParticle createTriangle(bool randomY)

osu.Game/Graphics/Backgrounds/TrianglesV2.cs

@@ -91,12 +91,14 @@ namespace osu.Game.Graphics.Backgrounds
         {
             base.Update();
 
-            Invalidate(Invalidation.DrawNode);
-
             if (CreateNewTriangles)
                 addTriangles(false);
 
             float elapsedSeconds = (float)Time.Elapsed / 1000;
+
+            if (elapsedSeconds == 0)
+                return;
+
             // Since position is relative, the velocity needs to scale inversely with DrawHeight.
             float movedDistance = -elapsedSeconds * Velocity * base_velocity / DrawHeight;
 
@@ -112,6 +114,8 @@ namespace osu.Game.Graphics.Backgrounds
                 if (bottomPos < 0)
                     parts.RemoveAt(i);
             }
+
+            Invalidate(Invalidation.DrawNode);
         }
 
         /// <summary>
@@ -138,8 +142,13 @@ namespace osu.Game.Graphics.Backgrounds
 
             int currentCount = parts.Count;
 
+            if (AimCount - currentCount == 0)
+                return;
+
             for (int i = 0; i < AimCount - currentCount; i++)
                 parts.Add(createTriangle(randomY));
+
+            Invalidate(Invalidation.DrawNode);
         }
 
         private TriangleParticle createTriangle(bool randomY)