Add :use_cursor option to PrawnOutputter, which makes it use and upda…

…te Prawn's built-in cursor

This lets you output a human-readable barcode like this:

barcode = Barby::QrCode.new("http://toretore.eu/barby/")
Prawn::Document.generate("test.pdf") do |pdf|
  pdf.text "Visit this website:"
  barcode.annotate_pdf(pdf, :use_cursor => true)
  pdf.text barcode.data
end

lib/barby/outputter/prawn_outputter.rb

@@ -7,7 +7,7 @@ class PrawnOutputter < Outputter
 
     register :to_pdf, :annotate_pdf
 
-    attr_accessor :xdim, :ydim, :x, :y, :height, :margin, :unbleed
+    attr_accessor :xdim, :ydim, :x, :y, :height, :margin, :unbleed, :use_cursor
 
 
     def to_pdf(opts={})
@@ -19,9 +19,15 @@ def to_pdf(opts={})
 
     def annotate_pdf(pdf, opts={})
       with_options opts do
-        xpos, ypos = x, y
+        xpos = x
         orig_xpos = xpos
 
+        if use_cursor
+          ypos = pdf.y - pdf.bounds.absolute_bottom - height - margin
+        else
+          ypos = y
+        end
+
         if barcode.two_dimensional?
           boolean_groups.reverse_each do |groups|
             groups.each do |bar,amount|
@@ -52,6 +58,8 @@ def annotate_pdf(pdf, opts={})
           end
         end
 
+        pdf.move_down(full_height) if use_cursor
+
       end
 
       pdf