Only pass Tf operator what it needs

Author: camelpunch

lib/mudbrick/content_stream/tf.ex

@@ -1,12 +1,12 @@
 defmodule Mudbrick.ContentStream.Tf do
   @moduledoc false
-  @enforce_keys [:font, :size]
-  defstruct [:font, :size]
+  @enforce_keys [:font_identifier, :size]
+  defstruct [:font_identifier, :size]
 
   defimpl Mudbrick.Object do
     def to_iodata(tf) do
       [
-        Mudbrick.Object.to_iodata(tf.font.resource_identifier),
+        Mudbrick.Object.to_iodata(tf.font_identifier),
         " ",
         to_string(tf.size),
         " Tf"

lib/mudbrick/text_block/output.ex

@@ -24,7 +24,7 @@ defmodule Mudbrick.TextBlock.Output do
         } = tb
       ) do
     tl = %TL{leading: tb.leading}
-    tf = %Tf{font: font, size: font_size}
+    tf = %Tf{font_identifier: font.resource_identifier, size: font_size}
 
     %__MODULE__{position: position, font: font, font_size: font_size}
     |> end_block()
@@ -192,9 +192,9 @@ defmodule Mudbrick.TextBlock.Output do
 
   defp with_font(output, op, part) do
     output
-    |> add(%Tf{font: output.font, size: output.font_size})
+    |> add(%Tf{font_identifier: output.font.resource_identifier, size: output.font_size})
     |> add(op)
-    |> add(%Tf{font: part.font, size: part.font_size})
+    |> add(%Tf{font_identifier: part.font.resource_identifier, size: part.font_size})
   end
 
   defp colour(output, {r, g, b}) do