skew {
  float x=real(#pixel)
  float y=imag(#pixel)+real(#pixel)*@sf
  #pixel=x+flip(y)
default:
  param sf
    caption="skew factor"
    default=0.0
  endparam
}

stretch {
transform:
  #pixel=real(#pixel)+flip(imag(#pixel)*@ar)
default:
  param ar
    caption="aspect ratio"
    default=1.0
  endparam
}