Fix renderers can't batch vertices with the same blending parameters in some cases

osu.Framework/Graphics/Containers/CompositeDrawable_DrawNode.cs

@@ -176,6 +176,9 @@ private void updateQuadBatch(IRenderer renderer)
                     quadBatch = renderer.CreateQuadBatch<TexturedVertex2D>(100, 1000);
             }
 
+            // Children will set their own blending parameters.
+            internal override bool SetBlending => false;
+
             protected override void Draw(IRenderer renderer)
             {
                 updateQuadBatch(renderer);

osu.Framework/Graphics/DrawNode.cs

@@ -67,6 +67,11 @@ public virtual void ApplyState()
             InvalidationID = Source.InvalidationID;
         }
 
+        /// <summary>
+        /// Whether the renderer should set blending parameters of this <see cref="DrawNode"/>.
+        /// </summary>
+        internal virtual bool SetBlending => true;
+
         /// <summary>
         /// Draws this <see cref="DrawNode"/> to the screen.
         /// </summary>
@@ -76,7 +81,9 @@ public virtual void ApplyState()
         /// <param name="renderer">The renderer to draw with.</param>
         protected virtual void Draw(IRenderer renderer)
         {
-            renderer.SetBlend(DrawColourInfo.Blending);
+            if (SetBlending)
+                renderer.SetBlend(DrawColourInfo.Blending);
+
             renderer.BackbufferDepth.Set(drawDepth);
         }