For a LuaLaTeX package I need to read the kerning values of certain
character pairs as they are defined by the current font. If the Node
renderer is used, I can use the following code, where first_node and
second_node are glyph nodes:
local current_font = font.getfont(first_node.font)
local kern = 0
if current_font and current_font.resources
and current_font.resources.sequences then
for _, t in ipairs(current_font.resources.sequences) do
if t.features and t.features.kern and t.steps and t.steps[1]
and t.steps[1].coverage and t.steps[1].coverage[first_node.char]
and t.steps[1].coverage[first_node.char][second_node.char] then
kern = t.steps[1].coverage[first_node.char][second_node.char]
end
end
end
However, I cannot be sure that the Node renderer is used, it may be the
case that HarfBuzz is used. But with HarfBuzz the font structure is
different and the above code does not return the kerning value needed.
HarfBuzz defines a C function hb_font_glyph_h_kerning(), but this
function does not have a Lua equivalent (unlike others listed in section
13.1 of the LuaTeX manual).
Could anyone tell me how to get the kerning values with HarfBuzz?
