Thumbnail Jekyll plugin

gistfile1.rb

# Generates a thumbnail image and returns its path, given a path to the full image.
# Hacked from various existing plugins, particularly:
# https://github.com/mrdanadams/jekyll-thumbnailer/blob/master/thumbnail.rb
# https://github.com/10io/jekyll-thumbnailify/blob/master/jekyll-thumbnailify.rb
#
# Doesn't require ImageMagick, and instead uses the Apple Developer tool sips, so
# only works when generated on a Mac. Could easily replace sips with ImageMagick again.
#
# Usage:
# 
# <img src="{% thumbnail /path/to/local/image.png width 100 < %}" />
# 
#   or:
#
# <img src="{% thumbnail /path/to/local/image.png height 100 < %}" />
#
# Depending on whether you want to constrain by width or height.
# 

require 'fileutils'

# The image static file model understood by Jekyll
# This is a sub class of StaticFile. But instead of managing a unique
# name between the src file and the dest file, we have a src complete 
# path, a dest path and a dest file name.
class ImageStaticFile < Jekyll::StaticFile

  # Initialize a new StaticFile.
  #   +image_src+ is the complete path of the src image file. Eg. /foo/bar.png
  #   +image_dest_dir+ is the destination dir for the dest image file
  #   +image_dest_name+ is the String filename of the dest image file
  #
  # Returns <ImageStaticFile>
  def initialize(image_src, image_dest_dir, image_dest_name)
    @image_src = image_src
    @dir = image_dest_dir
    @name = image_dest_name
  end

  # Obtains source file path.
  # In this implementation, simply returns image_src
  def path
    File.join(@image_src)
  end
  
end


class Jekyll::Thumbnail < Liquid::Tag

  def initialize(tag_name, markup, tokens)
    if /(?<source>[^\s]+)\s+(?<dimension>(width|height))\s+(?<size>\d+)/i =~ markup
      @source = source
      @isHeight = (dimension == "height")
      @size = size
    end
    super
  end

  def render(context)
    if @source

      # parking
      source = @source
      size = @size

      source_path = ".#{source}"
      raise "#{source} is not readable" unless File.readable?(source_path)

      # Split up path and generate output path
      ext = File.extname(source)
      desc = "w#{@size}"
      if @isHeight
        desc = "h#{@size}"
      end
      thumbname = "#{File.basename(source_path, ext)}_thumb_#{desc}#{ext}"
      final_dest = "#{File.dirname(source)}/#{thumbname}"

      # Generate thumbs into a temporary directory for caching
      # TODO: How to do this properly without this crap temp directory?!
      temp_dest = "./.tmp#{final_dest}"

      # Only re-generate the thumb if it doesn't already exist in the temporary directory
      if !File.exists?(temp_dest) || File.mtime(temp_dest) <= File.mtime(source_path)

        # Generate the full directory path within the .tmp folder
        FileUtils.mkpath( File.dirname(temp_dest) )

        # Run Apple Developer image resizing tool
        if @isHeight
          `sips --resampleHeight #{size} #{source_path} --out #{temp_dest}`
        else
          `sips --resampleWidth #{size} #{source_path} --out #{temp_dest}`
        end

      end

      # Generate the static thumb image file and add it to the site
      static_file = ImageStaticFile.new(temp_dest, File.dirname(source), thumbname)
      site = context.registers[:site]
      site.static_files << static_file

      # Return the final path to the thumb
      final_dest
      
    else
      "Could not create thumbnail for #{source}. Usage: thumbnail /path/to/local/image.png 50x50<"
    end
  end
end


Liquid::Template.register_tag('thumbnail',   Jekyll::Thumbnail)