side = min(w/(lw+6), h/(lh+6)) -- leave some margin for buttons

  local w1, w2 = landscape_button_offsets()
  local h1, h2 = portrait_button_offsets()
  if Safe_width > Safe_height then
    side = min((w-w1-w2)/(1+lw+1+6), h/(lh+6))  -- leave 1 side between board and buttons
  else
    side = min(w/(lw+6), (h-h1-h2)/(1+lh+1+6))  -- leave 1 side between board and buttons
  end

  bside = min(left, top)

  if Safe_width > Safe_height then
    bside = min((w-w1-w2-side*(1+lw+1))/2, (h-side*lh)/2)
  else
    bside = min((h-h1-h2-side*(1+lh+1))/2, (w-side*lw)/2)
  end
end
-- space needed for buttons to the left and right
function landscape_button_offsets()
  local ns, ps = tostring('>>'), tostring('<<')
  local nw, pw = App.width(ns)+10, App.width(ps)+10
  return 10+pw+10, 10+nw+10
  -- we assume the level name and undo button will be within this width
end
-- space needed for buttons to the top and bottom
function portrait_button_offsets()
  return 10+Line_height+10, 10+Line_height+10