drawDetails.hasseGrob: no visible global function definition for
  'viewport'
drawDetails.hasseGrob: no visible global function definition for 'unit'
drawDetails.hasseGrob: no visible global function definition for
  'pushViewport'
drawDetails.hasseGrob: no visible global function definition for
  'grid.lines'
drawDetails.hasseGrob: no visible global function definition for
  'popViewport'
drawNode: no visible global function definition for 'viewport'
drawNode: no visible global function definition for 'pushViewport'
drawNode: no visible global function definition for 'grid.rect'
drawNode: no visible global function definition for 'grid.roundrect'
drawNode: no visible global function definition for 'grid.clip'
drawNode: no visible global function definition for 'convertWidth'
drawNode: no visible global function definition for 'stringWidth'
drawNode: no visible global function definition for 'unit'
drawNode: no visible global function definition for 'convertHeight'
drawNode: no visible global function definition for 'grid.text'
drawNode: no visible global function definition for 'gpar'
drawNode: no visible global function definition for 'popViewport'
generateRandomGraph: no visible global function definition for 'runif'
hasse: no visible global function definition for 'as'
hasse: no visible global function definition for 'graphAM'
hasse: no visible global function definition for 'subGraph'
hasse: no visible global function definition for 'grid.newpage'
hasse: no visible global function definition for 'grid.draw'
hasseGrob: no visible global function definition for 'grob'
nHi: no visible global function definition for 'unit'
nHi: no visible global function definition for 'convertY'
nWi: no visible global function definition for 'unit'
nWi: no visible global function definition for 'stringWidth'
nWi: no visible global function definition for 'convertX'
Undefined global functions or variables:
  as convertHeight convertWidth convertX convertY gpar graphAM
  grid.clip grid.draw grid.lines grid.newpage grid.rect grid.roundrect
  grid.text grob popViewport pushViewport runif stringWidth subGraph
  unit viewport
Consider adding
  importFrom("methods", "as")
  importFrom("stats", "runif")
to your NAMESPACE file (and ensure that your DESCRIPTION Imports field
contains 'methods').