Emoji cause text to extend beyond edge of bounding box

[xtian]

Rendering an emoji in a line causes it to extend beyond the boundaries of its containing bounding box.

Example:

[hidakatsuya]

@xtian Can you show me code of the example?

[xtian]

@hidakatsuya, here's the code where this is happening in my project:

@document.bounding_box [0.9.in, 1.1.in], { width: 6.in, height: 0.7.in } do
  @document.font 'Sentinel Book', size: 9 do
    @document.text text, align: :center, valign: :center, leading: 2, inline_format: true
  end
end

[hidakatsuya]

@xtian Thanks so much!

[hidakatsuya]

This problem is very difficult. There is no easy implementation to fix, but you may be able to resolve to use a Japanese font like ipag.ttf.

# Install ipag.ttf
@document.font_families.update('IPAGothic' => { normal: 'ipag.ttf' })
# :
@document.text 'foo bar <font name="IPAGothic">😀</font>', inline_format: true

[xtian]

Yeah, I looked into fixing this myself and couldn't find a straightforward way to do it. Frustrating!

Thanks for the Japanese font tip. I'm no longer working on the project where I was having this issue, but maybe it will help someone else.

Feel free to close this issue if you'd like.

[aried3r]

Hey! We're also facing this issue and were wondering if you have maybe some details where and why exactly this is happening, @hidakatsuya.

[hidakatsuya]

OK, please wait for a while as I will investigate this issue again.

[brandoncc]

Did you ever have a chance to look into this again?

[gettalong]

@aried3r @brandoncc @hidakatsuya This most certainly happens due to the line wrapping algorithm not knowing the size of the emoji images together with the missing width information for the emoji characters.

[brandoncc]

Thanks @gettalong!

[ggmomo]

I managed to make it work by overriding some methods from Prawn 2.3.0. The idea was to replace emojis with classic chars so Prawn manages to wrap lines correctly.
⚠️ Ipag ttf font must be set up when initializing a Prawn document.

Here is my (naive) proposal:

Requirements

• prawn 2.3.0
• prawn-emoji 5.0.0
• unicode-emoji
• ipag font

Prawn emoji

Fix cursor position by adding document.font_size instead of emoji_image.width.

Prawn::Emoji::Drawer.class_eval do
  def draw_emoji(emoji_char, at:)
    emoji_image = Emoji::Image.new(emoji_char)
    emoji_image.render(document, at: at)
  
    document.font_size + document.character_spacing
  end
end

Prawn

Copy this code into config/intitializers if running a Rails app.

# Replace emojis unicodes with char to fix the caclculation of the length
# you should use the same unicode emoji regex as the one set up in your prawn-emoji config
def replace_emojis_with_text(text)
  text.gsub(Unicode::Emoji::REGEX_WELL_FORMED_INCLUDE_TEXT) { 'XX' }
end

# Parse text and index emojis position and length in a hash
# example : {10 => 1, 35 => 5}
# means we have an emoji of length 1 at the index 10
# and we have an emoji of length 5 at the index 35
def index_emojis(text)
  emojis_indexes = {}

  text.to_enum(:scan, Unicode::Emoji::REGEX_WELL_FORMED_INCLUDE_TEXT).map do |m|
    m.length.times do |i|
      emojis_indexes[$`.size + i] = i.zero? ? m.length : 0
    end
  end

  emojis_indexes
end

Prawn::Text::Formatted::Arranger.class_eval do
  # This method repositions the x cursor after writing text fragments
  def fragment_measurements=(fragment)
    apply_font_settings(fragment) do
      fragment.width = @document.width_of(
        replace_emojis_with_text(fragment.text),
        kerning: @kerning
      )
      fragment.line_height = @document.font.height
      fragment.descender   = @document.font.descender
      fragment.ascender    = @document.font.ascender
    end
  end
end

Prawn::Text::Formatted::LineWrap.class_eval do
  # render char if line has enough space left
  def append_char(char)
    # kerning doesn't make sense in the context of a single character
    char_width = @document.width_of(replace_emojis_with_text(char))

    if @accumulated_width + char_width <= @width
      @accumulated_width += char_width
      @fragment_output << char
      true
    else
      false
    end
  end

  # parse segment and tries to render char
  def wrap_by_char(segment)
    emojis_indexes = index_emojis(segment)

    segment.each_char.with_index do |char, index|
      if emojis_indexes[index].present?
        # if length == 0, emoji has already been processed
        next if emojis_indexes[index].zero?

        char = segment[index, emojis_indexes[index]]
      end
      break unless append_char(char)
    end
  end

  # Regex to test if text contains more than one word
  def scan_pattern(encoding = ::Encoding::UTF_8)
    ebc = break_chars(encoding)
    eshy = soft_hyphen(encoding)
    ehy = hyphen(encoding)
    ews = whitespace(encoding)

    patterns = [
      "[^#{ebc}]+#{eshy}",
      "[^#{ebc}]+#{ehy}+",
      "[^#{ebc}]+",
      "[#{ews}]+",
      "#{ehy}+[^#{ebc}]*",
      eshy.to_s
    ]

    pattern = patterns
      .map { |p| p.encode(encoding) }
      .join('|')

    Regexp.new("#{Unicode::Emoji::REGEX_WELL_FORMED_INCLUDE_TEXT}|#{pattern}")
  end

  # This method calculates the line remaining space to decide when to start a new line
  def add_fragment_to_line(fragment)
    if fragment == ''
      true
    elsif fragment == "\n"
      @newline_encountered = true
      false
    else
      tokenize(fragment).each do |segment|
        segment_width = if segment == zero_width_space(segment.encoding)
                          0
                        else
                          @document.width_of(replace_emojis_with_text(segment), kerning: @kerning)
                        end

        if @accumulated_width + segment_width <= @width
          @accumulated_width += segment_width
          shy = soft_hyphen(segment.encoding)
          if segment[-1] == shy
            sh_width = @document.width_of(shy, kerning: @kerning)
            @accumulated_width -= sh_width
          end
          @fragment_output += segment
        else
          if @accumulated_width.zero? && @line_contains_more_than_one_word
            @line_contains_more_than_one_word = false
          end
          end_of_the_line_reached(segment)
          fragment_finished(fragment)
          return false
        end
      end

      fragment_finished(fragment)
      true
    end
  end
end

Prawn::Text::Formatted::Box.class_eval do
  # This methods parses the text and test that every char symbol is included in the current font
  # If a symbol is not included it is going to parse the provided fallback fonts
  # We needed to override this method so it does not break in half our Emojis
  # We also forced the font 'ipag' on the Emojis so they can be properly rendered in a text box
  def analyze_glyphs_for_fallback_font_support(hash)
    font_glyph_pairs = []
    original_font    = @document.font.family
    fragment_font    = hash[:font] || original_font
    fallback_fonts   = @fallback_fonts.dup

    # always default back to the current font if the glyph is missing from
    # all fonts
    fallback_fonts << fragment_font

    @document.save_font do
      emojis_indexes = index_emojis(hash[:text])

      # parse each char to test if we need to use a fallback font
      hash[:text].each_char.with_index do |char, index|
        if emojis_indexes[index].present?
          # if length == 0, emoji has already been processed
          next if emojis_indexes[index].zero?

          # Force japanese font ipag on emojis
          font_glyph_pairs << [
            'ipag', hash[:text][index, emojis_indexes[index]]
          ]
        else
          font_glyph_pairs << [
            find_font_for_this_glyph(
              char,
              fragment_font,
              fallback_fonts.dup
            ),
            char
          ]
        end
      end
    end

    # Don't add a :font to fragments if it wasn't there originally
    if hash[:font].nil?
      font_glyph_pairs.each do |pair|
        pair[0] = nil if pair[0] == original_font
      end
    end

    form_fragments_from_like_font_glyph_pairs(font_glyph_pairs, hash)
  end
end

Hoping this can help 🙏