Layer2D


  PROTO Layer2D[
          eventIn         MFNode          addChildren
          eventIn         MFNode          removeChildren
          exposedField    MFNode          children            []
  
          exposedField    SFVec2f         translation 0 0  
          exposedField    SFVec2f         size            -1 -1   
          exposedField    SFNode          background      NULL
          exposedField    SFNode          viewport        NULL
          ]