feat: Adds viewBox option for SVG

Thanks to @mjy @MattDahEpic and #98 and #66

README.md

@@ -92,6 +92,9 @@ shape_rendering - SVG Attribute: auto | optimizeSpeed | crispEdges | geometricPr
                   (defaults crispEdges)
 standalone      - whether to make this a full SVG file, or only an svg to embed in other svg
                   (default true)
+viewbox         - replace `svg.width` and `svg.height` attribute with `svg.viewBox` to
+                  allow CSS scaling
+                  (default false)
 ```
 Example
 ```ruby

lib/rqrcode/export/svg.rb

@@ -16,19 +16,23 @@ module SVG
       # shape_rendering - Defaults to crispEdges
       # standalone - wether to make this a full SVG file, or only svg to embed
       #              in other svg.
+      # viewbox    - replace `width` and `height` in <svg> with a viewBox, allows CSS scaling
       #
       def as_svg(options = {})
         offset = options[:offset].to_i || 0
         color = options[:color] || "000"
         shape_rendering = options[:shape_rendering] || "crispEdges"
         module_size = options[:module_size] || 11
         standalone = options[:standalone].nil? ? true : options[:standalone]
+        viewbox = options[:viewbox].nil? ? false : options[:viewbox]
 
         # height and width dependent on offset and QR complexity
         dimension = (@qrcode.module_count * module_size) + (2 * offset)
+        # use dimensions differently if we are using a viewBox
+        dimensions_attr = viewbox ? %(viewBox="0 0 #{dimension} #{dimension}") : %(width="#{dimension}" height="#{dimension}")
 
         xml_tag = %(<?xml version="1.0" standalone="yes"?>)
-        open_tag = %(<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ev="http://www.w3.org/2001/xml-events" width="#{dimension}" height="#{dimension}" shape-rendering="#{shape_rendering}">)
+        open_tag = %(<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ev="http://www.w3.org/2001/xml-events" #{dimensions_attr} shape-rendering="#{shape_rendering}">)
         close_tag = "</svg>"
 
         result = []

spec/rqrcode/export_svg_spec.rb

@@ -30,5 +30,14 @@
       expect(doc).not_to match(%r{<svg.*>})
       expect(doc).not_to match(%r{</svg>})
     end
+
+    it "renders viewBox and not height/width when `viewbox` is `true`" do
+      doc = RQRCode::QRCode.new("qrcode").as_svg(viewbox: true)
+      # For now we do very naive pattern matching. The alternative is to
+      # include a librariry for parsing XML, like nokogiri. That is a big
+      # change for such a small test, though.
+      expect(doc).not_to match(%r{<\?xml.*height="\d+".*width=})
+      expect(doc).to match(%r{<svg.*viewBox="(\d+\s?){4}"})
+    end
   end
 end