the filter base file was missing, my bad (thanks Joel)

lib/locomotive/liquid/filters/base.rb

@@ -0,0 +1,47 @@
+module Locomotive
+  module Liquid
+    module Filters
+      module Base
+
+        protected
+
+        # Convert an array of properties ('key:value') into a hash
+        # Ex: ['width:50', 'height:100'] => { :width => '50', :height => '100' }
+        def args_to_options(*args)
+          options = {}
+          args.flatten.each do |a|
+            if (a =~ /^(.*):(.*)$/)
+              options[$1.to_sym] = $2
+            end
+          end
+          options
+        end
+
+        # Write options (Hash) into a string according to the following pattern:
+        # <key1>="<value1>", <key2>="<value2", ...etc
+        def inline_options(options = {})
+          return '' if options.empty?
+          (options.stringify_keys.sort.to_a.collect { |a, b| "#{a}=\"#{b}\"" }).join(' ') << ' '
+        end
+
+        # Get the url to be used in html tags such as image_tag, flash_tag, ...etc
+        # input: url (String) OR asset drop
+        def get_url_from_asset(input)
+          input.respond_to?(:url) ? input.url : input
+        end
+
+        def asset_url(path)
+          ThemeAssetUploader.url_for(@context.registers[:site], path)
+        end
+
+        def absolute_url(url)
+          url.starts_with?('/') ? url : "/#{url}"
+        end
+
+      end
+
+      ::Liquid::Template.register_filter(Base)
+
+    end
+  end
+end