Centre-alignment

Author: camelpunch

lib/mudbrick.ex

@@ -215,7 +215,9 @@ defmodule Mudbrick do
   - `:position` - Coordinates from bottom-left of page in points. Default: `{0, 0}`.
   - `:font_size` - Size in points. Default: `12`.
   - `:leading` - Leading in points. Default is 120% of `:font_size`.
-  - `:align` - Either `:left` or `:right`. Default: `:left`. Note that the rightmost point of right-aligned text is the horizontal offset provided to `:position`.
+  - `:align` - `:left`, `:right` or `:centre`. Default: `:left`.
+    Note that the rightmost point of right-aligned text is the horizontal offset provided to `:position`.
+    The same position defines the centre point of centre-aligned text.
 
   ## Individual write options
 
@@ -253,43 +255,56 @@ defmodule Mudbrick do
       ...> |> page()
       ...> |> text(["I am ", {"bold", font: :bold}], font: :regular, position: {200, 200})
 
-  Underlined text.
+  [Underlined text](examples/underlined_text.pdf?#navpanes=0).
 
       iex> import Mudbrick
       ...> new(fonts: %{bodoni: Mudbrick.TestHelper.bodoni_regular()})
       ...> |> page(size: {100, 50})
       ...> |> text([
-      ...>      {"heading\\n", leading: 20},
-      ...>      "nounderline\\n",
-      ...>      "now ",
-      ...>      {"underline", underline: [width: 1]},
-      ...>      " that"
+      ...>      {"the\\n", leading: 20},
+      ...>      "quick\\n",
+      ...>      "brown fox ",
+      ...>      {"jumps", underline: [width: 1]},
+      ...>      " over"
       ...>    ], position: {8, 40}, font_size: 8)
       ...> |> render()
       ...> |> then(&File.write("examples/underlined_text.pdf", &1))
 
-  Produces [this PDF](examples/underlined_text.pdf?#navpanes=0).
-
   <object width="400" height="130" data="examples/underlined_text.pdf?#navpanes=0" type="application/pdf"></object>
 
-  Underlined, right-aligned text.
+  [Underlined, right-aligned text](examples/underlined_text_right_align.pdf?#navpanes=0).
 
       iex> import Mudbrick
       ...> new(fonts: %{bodoni: Mudbrick.TestHelper.bodoni_regular()})
       ...> |> page(size: {100, 50})
       ...> |> text([
-      ...>      {"heading\\n", leading: 20},
-      ...>      "nounderline\\n",
-      ...>      "now ",
-      ...>      {"underline", underline: [width: 1]},
-      ...>      " that"
+      ...>      {"the\\n", leading: 20},
+      ...>      "quick\\n",
+      ...>      "brown fox ",
+      ...>      {"jumps", underline: [width: 1]},
+      ...>      " over"
       ...>    ], position: {90, 40}, font_size: 8, align: :right)
       ...> |> render()
       ...> |> then(&File.write("examples/underlined_text_right_align.pdf", &1))
 
-  Produces [this PDF](examples/underlined_text_right_align.pdf?#navpanes=0).
-
   <object width="400" height="130" data="examples/underlined_text_right_align.pdf?#navpanes=0" type="application/pdf"></object>
+
+  [Underlined, centre-aligned text](examples/underlined_text_centre_align.pdf?#navpanes=0).
+
+      iex> import Mudbrick
+      ...> new(fonts: %{bodoni: Mudbrick.TestHelper.bodoni_regular()})
+      ...> |> page(size: {100, 50})
+      ...> |> text([
+      ...>      {"the\\n", leading: 20},
+      ...>      "quick\\n",
+      ...>      "brown fox ",
+      ...>      {"jumps", underline: [width: 1]},
+      ...>      " over"
+      ...>    ], position: {50, 40}, font_size: 8, align: :centre)
+      ...> |> render()
+      ...> |> then(&File.write("examples/underlined_text_centre_align.pdf", &1))
+
+  <object width="400" height="130" data="examples/underlined_text_centre_align.pdf?#navpanes=0" type="application/pdf"></object>
   """
 
   @spec text(context(), Mudbrick.TextBlock.write(), Mudbrick.TextBlock.options()) :: context()

lib/mudbrick/text_block/output.ex

@@ -30,7 +30,11 @@ defmodule Mudbrick.TextBlock.Output do
     |> end_block()
     |> reduce_lines(
       tb.lines,
-      if(tb.align == :left, do: fn _ -> 0 end, else: &Line.width/1)
+      case tb.align do
+        :left -> fn _ -> 0 end
+        :right -> &Line.width/1
+        :centre -> fn line -> Line.width(line) / 2 end
+      end
     )
     |> td(position)
     |> add(tl)

test/mudbrick/text_block_test.exs

@@ -520,6 +520,25 @@ defmodule Mudbrick.TextBlockTest do
     end
   end
 
+  describe "centre-aligned" do
+    test "offset of a line is half the right-aligned offset" do
+      text = "aaaa"
+      size = 12
+      right_td = first_td(:right, text, size)
+      centre_td = first_td(:centre, text, size)
+
+      assert centre_td.tx == right_td.tx / 2
+    end
+  end
+
+  defp first_td(align, text, size) do
+    output(fn %{fonts: fonts} ->
+      TextBlock.new(align: align, font: fonts.regular, font_size: size)
+      |> TextBlock.write(text)
+    end)
+    |> Enum.find(&match?(%Mudbrick.ContentStream.Td{}, &1))
+  end
+
   defp output(f) do
     Mudbrick.TestHelper.wrapped_output(f, TextBlock.Output) |> Enum.reverse()
   end