anchor.diff:          OpenGL.Hl.Assert ()
   
           // next pool
  +        env.SpriteIndex <- 0
           Pool.next env.Pool
  -        env.SpriteIndex <- 0
   
       let CreateEnv () =
           let (texUniform, shader) = CreateShader ()
  
positive.code:               Pool : Pool
                mutable State : State }
  
      /// Create a sprite batch shader with uniforms:
      ///     0: sampler2D tex
      /// and attributes:
      ///     0: vec2 position
  
negative.code:             for context in pool.Contexts do
                  Context.destroy context
              pool.Contexts.Clear ()
              pool.ContextIndex <- 0
  
          static member next pool =
              pool.ContextIndex <- inc pool.ContextIndex
  
          static member reset pool =
              pool.ContextIndex <- 0
  
          member this.Current =
              while this.ContextIndex >= this.Contexts.Count do this.Contexts.Add (Context.create this.SpriteMax)
              this.Contexts.[this.ContextIndex]
  
      type [<StructuralEquality; NoComparison>] private State =
          { BlendingFactorSrc : OpenGL.BlendingFactor
  