image_tag_with_auto_size.rb

gem "fastimage", "~>1.2.13"

module ApplicationHelper
  include ActionView::Helpers::AssetTagHelper

  # 画像サイズ見て自動でwidth/height属性つけるimage_tag
  def image_tag_with_auto_size(source, options)
    if options[:size] || options[:width] || options[:height]
      image_tag_without_auto_size(source, options)
    else
      begin
        width, height = FastImage.size(File.join(Rails.root, 'public', source))

        if request.smart_phone?
          width /= 2
          height /= 2
        end

        image_tag_without_auto_size(source, options.merge(width: width, height: height))
      rescue FastImage::FastImageException => e
        Rails.logger.error("FastImage.size failed: #{e.inspect}")

        image_tag_without_auto_size(source, options)
      end
    end
  end
  alias_method_chain :image_tag, :auto_size
end