anchor.diff:          let mutable start = V2d.NaN
           let currentPoints = List<V2d>()
           let innerPoints = List<List<V2d>>()
  -
           let lines = List<Line2d>()
   
           let last() = innerPoints.[innerPoints.Count-1]
  
positive.code: 
              if close then
                  if start <> p then
                      last().Add(start)
                      lines.Add(Line2d(p, start))
  
                  currentPoints.Clear()
                  start <- V2d.NaN
                          
  
negative.code: 
  
          let sg =
              Glyph.geometry font '@' 
                  |> Sg.ofIndexedGeometry
                  |> Sg.effect [
                      DefaultSurfaces.trafo |> toEffect
  