anchor.diff:              let cpuOffset = cpuOffset + vertexSize
               Marshal.StructureToPtr<Vertex> (vertex2, cpuOffset, false)
   
  +            // advance sprite index
               env.SpriteIndex <-inc env.SpriteIndex
   
           let EndFrame env =
  
positive.code:                 | FlipV -> v2 1.0f 1.0f
                  | FlipHV -> v2 -1.0f 1.0f
  
              let position0 = (position - center).Rotate rotation + center
              let mutable vertex0 = Unchecked.defaultof<Vertex>
              vertex0.Position <- position0
              vertex0.Coords <- coords.BottomLeft * flipper
              vertex0.Color <- color
  
              let position1Unrotated = v2 (position.X + size.X) position.Y
              let position1 = (position1Unrotated - center).Rotate rotation + center
              let mutable vertex1 = Unchecked.defaultof<Vertex>
              vertex1.Position <- position1
              vertex1.Coords <- coords.BottomRight * flipper
              vertex1.Color <- color
  
              let position2Unrotated = v2 (position.X + size.X) (position.Y + size.Y)
              let position2 = (position2Unrotated - center).Rotate rotation + center
              let mutable vertex2 = Unchecked.defaultof<Vertex>
              vertex2.Position <- position2
              vertex2.Coords <- coords.TopRight * flipper
              vertex2.Color <- color
  
              let position3Unrotated = v2 position.X (position.Y + size.Y)
              let position3 = (position3Unrotated - center).Rotate rotation + center
              let mutable vertex3 = Unchecked.defaultof<Vertex>
              vertex3.Position <- position3
              vertex3.Coords <- coords.TopLeft * flipper
              vertex3.Color <- color
  
              // TODO: 3D: consider using an EBO to reduce bus utilization.
              // TODO: 3D: consider using a single pre-allocated SpriteVectex[6] to reduce marshaling calls.
              let vertexSize = nativeint sizeof<Vertex>
  
negative.code:                   Pool : Pool
                    mutable State : State }
  
          let private Flush env =
  
              // setup state
  