\input luaotfload.sty

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% math dimension getter
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\font\xitsmath=file:xits-math.otf
\font\cambriamath=file:cambria.ttc(1)

\font\main=file:Iwona-Regular.otf at 12pt\main

\directlua{
  local aux = luaotfload.aux
  local test_a = function (fontname, dimension)
    tex.sprint(
      "(", fontname, " (", dimension, " ",
      aux.get_math_dimension(fontname, dimension),
      [[))\endgraf ]])
  end
    
  local test_b = function (fontname, dimension)
    aux.sprint_math_dimension(fontname, dimension)
    tex.print[[\endgraf ]]
  end

  test_a("xitsmath",     "AxisHeight")
  test_a("xitsmath",     "RadicalVerticalGap")
  test_a("cambriamath",  "StackTopShiftUp")
  test_a("cambriamath",  "FractionNumeratorGapMin")

  test_b("xitsmath",     "AxisHeight")
  test_b("xitsmath",     "RadicalVerticalGap")
  test_b("cambriamath",  "StackTopShiftUp")
  test_b("cambriamath",  "FractionNumeratorGapMin")
}

foo bar baz

\bye
