I currenly learning Elixir and want to manipulate images with it. I use :egd to calculate sizes of text image that I will render.

My code produces this error:

** (MatchError) no match of right hand side value: []
    (egd 0.10.0) c:/expro/image_text/deps/egd/src/egd_font.erl:62: :egd_font.glyph/2
    (egd 0.10.0) c:/expro/image_text/deps/egd/src/egd_render.erl:601: :egd_render.text_intervals/5
    (egd 0.10.0) c:/expro/image_text/deps/egd/src/egd_render.erl:339: :egd_render.precompile_objects/1
    (egd 0.10.0) c:/expro/image_text/deps/egd/src/egd_render.erl:317: :egd_render.precompile/1
    (egd 0.10.0) c:/expro/image_text/deps/egd/src/egd_render.erl:39: :egd_render.binary/2
    (egd 0.10.0) c:/expro/image_text/deps/egd/src/egd.erl:239: :egd.loop/1

My code:

defmodule ImageText do
  @moduledoc """
  Documentation for `ImageText`.
  """

  def main() do
    render_text("hello")
  end

  def font() do
    :egd_font.load("lib/fonts/font.wingsfont")
  end

  def render_text(text) do
    {image_width, image_height} = calculate_text_size(text)
    image = :egd.create(image_width, image_height)
    :egd.text(image, {0, 0}, font(), String.graphemes(text), :black)
    :egd.save(:egd.render(image), "lib/image.png")
    :egd.destroy(image)
  end

  def calculate_text_size(text) do
    {font_width, font_height} = :egd_font.size(font())

    {font_width * String.length(text), font_height}
  end
end

lib/fonts/font.wingsfont.ttf is https://github.com/erlang/egd/blob/master/priv/fonts/6x11_latin1.wingsfont