anchor.diff:          let heightSampler =
               sampler2d {
                   texture uniform?HeightFieldTexture
  -                filter Filter.MinMagLinear
  +                filter Filter.Anisotropic
                   addressU WrapMode.Clamp
                   addressV WrapMode.Clamp
               }
   
           let planeSize = 10.0
           let heightScale = 0.5
  -        let pixelSize = 2.0
  +        let pixelSize = 5.0
   
           [<ReflectedDefinition>]
           let sampleHeight (world : V4d)  =
  
positive.code:                 }
              }
  
  
  
      [<Demo("PGM")>]
  
negative.code:         )
  
          
          tessGrid 128
              |> Sg.ofIndexedGeometry
              |> Sg.effect [
                  DefaultSurfaces.trafo |> toEffect 
                  Shader.hTessControl |> toEffect
                  Shader.hTessEval |> toEffect
                  //Shader.hGeometry |> toEffect
                  DefaultSurfaces.constantColor C4f.White |> toEffect
                  DefaultSurfaces.diffuseTexture |> toEffect
  //                DefaultSurfaces.simpleLighting |> toEffect 
  