anchor.diff:  
               let position0 = (position - center).Rotate rotation + center
               let mutable vertex0 = Unchecked.defaultof<Vertex>
  -            vertex0.Pos <- position0
  +            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.Pos <- position1
  +            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.Pos <- position2
  +            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.Pos <- position3
  +            vertex3.Position <- position3
               vertex3.Coords <- coords.TopLeft * flipper
               vertex3.Color <- color
   
  
positive.code:         let samplerFragmentShaderStr =
              [Constants.Render.GlslVersionPragma
               "uniform sampler2D tex;"
               "in vec2 coord;"
               "in vec4 color;"
               "out vec4 frag;"
               "void main()"
               "{"
               "  frag = color * texture(tex, coord);"
               "}"] |> String.join "\n"
  
          // create shader program
  
negative.code: 
          type [<StructuralEquality; NoComparison; StructLayout (LayoutKind.Sequential)>] private Vertex =
              struct
                  val mutable Position : Vector2
                  val mutable Coords : Vector2
                  val mutable Color : Color
                  end
  