I’m trying to print text centred around a point.

At the moment my code offsets the x coordinate by half the width
of a string in pixels, calculated as (4* #s)-1.

This works fine for
alphanumeric text but is wrong when the text contains glyphs.

Is there a built in function to help achieve this?

Or do I need to examine every character when computing the pixel width of the text?

Unfortunately, you pretty much have to watch out for those double-wide glyphs.

I'd suggest either minimizing your use of glyphs or making a function that returns the proper width of a string.

Of course, a more ridiculous hack way could be something like this:

function center_text(string, y, c)
  local x = 64 - (#string * 2)

  if(c)color(c)

  for i = 1, #string do
    print(sub(string, i, i), x, y)
    x += 4
  end
end

function _draw()
  cls(7)
  color(8)
  center_text("😐  hello, world! 😐 ", 60)
  -- Note the extra space after each glyph
end

I put this together in a minute, so it might not be the best.

Cunning!

I ended up taking the width of glyphs into account like this:

-- centered printing

-- width of a printed string
function printw(s)
  if #s == 0 then 
    return 0
  end

  w = 0
  for i = 1, #s do
    if sub(s,i,i) >= "\x80" then
      w += 7
    else 
      w += 3
    end
  end

  return w + #s - 1
end

-- print centered
function printc(s, x, y)
  print(s, x - printw(s)/2, y)
end

And that's working well