anchor.diff:                  let pm = offset + v.p.XY * scale
   
                   if flip then
  -                    let t = V3d(trafo.M03, trafo.M13, trafo.M23)
  -                    let z = V3d(trafo.M02, trafo.M12, trafo.M22)
  - 
  -                    if Vec.dot t z <= 0.0 then
  +                    if keepsWinding (isOrtho uniform.ProjTrafo) trafo then
                           p <- trafo * V4d( pm.X, pm.Y, v.p.Z, v.p.W)
                       else
                           p <- trafo * V4d(-pm.X, pm.Y, v.p.Z, v.p.W)
  
positive.code: 
                  [<TrafoOffsetAndScale>] instanceTrafo : M34d
              }
              
  
          let pathVertex (v : Vertex) =
              vertex {
                  let trafo = uniform.ModelViewTrafo
  
negative.code:                 let pm = offset + v.p.XY * scale
  
                  if flip then
                      if keepsWinding (isOrtho uniform.ProjTrafo) trafo then
                          p <- trafo * V4d( pm.X, pm.Y, v.p.Z, v.p.W)
                      else
                          p <- trafo * V4d(-pm.X, pm.Y, v.p.Z, v.p.W)
  