Basic implementation of linearGradient

If you've got Prawn 2.0.3+ (currently unreleased at the time of this commit),
you can get linear gradients, in both units (userSpaceOnUse and
objectBoundingBox).  gradientTransform, spreadMethod and stop-opacity on the
stop tag are all unimplemented.

README.md

@@ -49,10 +49,13 @@ prawn-svg supports most but not all of the full SVG 1.1 specification.  It curre
 
  - <tt>&lt;style&gt;</tt> plus <tt>id</tt>, <tt>class</tt> and <tt>style</tt> attributes (see CSS section below)
 
- - <tt>&lt;image&gt;</tt> with <tt>http:</tt>, <tt>https:</tt> and <tt>data:image/*;base64</tt> schemes
+ - <tt>&lt;image&gt;</tt> with <tt>http:</tt>, <tt>https:</tt> and <tt>data:image/\*;base64</tt> schemes
 
  - <tt>&lt;clipPath&gt;</tt>
 
+ - <tt>&lt;linearGradient&gt;</tt> but only with Prawn 2.0.3+. gradientTransform, spreadMethod and stop-opacity are
+   unimplemented.
+
  - attributes/styles: <tt>fill</tt>, <tt>stroke</tt>, <tt>stroke-width</tt>, <tt>stroke-linecap</tt>, <tt>stroke-dasharray</tt>, <tt>opacity</tt>, <tt>fill-opacity</tt>, <tt>stroke-opacity</tt>, <tt>transform</tt>, <tt>clip-path</tt>, <tt>display</tt>
 
  - the <tt>viewBox</tt> attribute on the <tt>&lt;svg&gt;</tt> tag
@@ -73,7 +76,7 @@ prawn-svg uses the css_parser gem to parse CSS <tt>&lt;style&gt;</tt> blocks.  I
 
 ## Not supported
 
-prawn-svg does not support external <tt>url()</tt> references, measurements in <tt>en</tt> or <tt>em</tt>, sub-viewports, gradients/patterns or markers.
+prawn-svg does not support external <tt>url()</tt> references, measurements in <tt>en</tt> or <tt>em</tt>, sub-viewports, radial gradients, patterns or markers.
 
 ## Configuration
 

lib/prawn/svg/color.rb

@@ -1,5 +1,17 @@
 class Prawn::SVG::Color
-  UnresolvableURLWithNoFallbackError = Class.new(StandardError)
+  class Hex
+    attr_reader :value
+
+    def initialize(value)
+      @value = value
+    end
+
+    def ==(other)
+      value == other.value
+    end
+  end
+
+  DEFAULT_COLOR = Hex.new("000000")
 
   HTML_COLORS = {
     'aliceblue' => 'f0f8ff',
@@ -153,34 +165,52 @@ class Prawn::SVG::Color
 
   RGB_VALUE_REGEXP = "\s*(-?[0-9.]+%?)\s*"
   RGB_REGEXP = /\Argb\(#{RGB_VALUE_REGEXP},#{RGB_VALUE_REGEXP},#{RGB_VALUE_REGEXP}\)\z/i
-  URL_REGEXP = /\Aurl\([^)]*\)\z/i
+  URL_REGEXP = /\Aurl\(([^)]*)\)\z/i
 
-  def self.color_to_hex(color_string)
+  def self.parse(color_string, gradients = nil)
     url_specified = false
 
-    result = color_string.strip.scan(/([^(\s]+(\([^)]*\))?)/).detect do |color, *_|
+    components = color_string.to_s.strip.scan(/([^(\s]+(\([^)]*\))?)/)
+
+    result = components.map do |color, *_|
       if m = color.match(/\A#([0-9a-f])([0-9a-f])([0-9a-f])\z/i)
-        break "#{m[1] * 2}#{m[2] * 2}#{m[3] * 2}"
+        Hex.new("#{m[1] * 2}#{m[2] * 2}#{m[3] * 2}")
+
       elsif color.match(/\A#[0-9a-f]{6}\z/i)
-        break color[1..6]
+        Hex.new(color[1..6])
+
       elsif hex = HTML_COLORS[color.downcase]
-        break hex
+        Hex.new(hex)
+
       elsif m = color.match(RGB_REGEXP)
-        break (1..3).collect do |n|
+        hex = (1..3).collect do |n|
           value = m[n].to_f
           value *= 2.55 if m[n][-1..-1] == '%'
           "%02x" % clamp(value.round, 0, 255)
         end.join
-      elsif color.match(URL_REGEXP)
+
+        Hex.new(hex)
+
+      elsif matches = color.match(URL_REGEXP)
         url_specified = true
-        nil # we can't handle these so we find the next thing that matches
+        url = matches[1]
+        if url[0] == "#" && gradients && gradient = gradients[url[1..-1]]
+          gradient
+        end
       end
     end
 
-    # http://www.w3.org/TR/SVG/painting.html section 11.2
-    raise UnresolvableURLWithNoFallbackError if result.nil? && url_specified
+    # Generally, we default to black if the colour was unparseable.
+    # http://www.w3.org/TR/SVG/painting.html section 11.2 says if a URL was
+    # supplied without a fallback, that's an error.
+    result << DEFAULT_COLOR unless url_specified
+
+    result.compact
+  end
 
-    result
+  def self.color_to_hex(color)
+    result = parse(color).detect {|result| result.is_a?(Hex)}
+    result.value if result
   end
 
   protected

lib/prawn/svg/document.rb

@@ -15,7 +15,7 @@ class Prawn::SVG::Document
   attr_reader :root,
     :sizing,
     :cache_images, :fallback_font_name,
-    :css_parser, :elements_by_id
+    :css_parser, :elements_by_id, :gradients
 
   def initialize(data, bounds, options)
     @css_parser = CssParser::Parser.new if CSS_PARSER_LOADED
@@ -24,6 +24,7 @@ def initialize(data, bounds, options)
     @warnings = []
     @options = options
     @elements_by_id = {}
+    @gradients = {}
     @cache_images = options[:cache_images]
     @fallback_font_name = options.fetch(:fallback_font_name, DEFAULT_FALLBACK_FONT_NAME)
 

lib/prawn/svg/elements.rb

@@ -2,7 +2,7 @@ module Prawn::SVG::Elements
   COMMA_WSP_REGEXP = /(?:\s+,?\s*|,\s*)/
 end
 
-%w(base root container style text line polyline polygon circle ellipse rect path use image ignored).each do |filename|
+%w(base root container style text line polyline polygon circle ellipse rect path use image gradient ignored).each do |filename|
   require "prawn/svg/elements/#{filename}"
 end
 
@@ -24,6 +24,7 @@ module Prawn::SVG::Elements
     path: Prawn::SVG::Elements::Path,
     use: Prawn::SVG::Elements::Use,
     image: Prawn::SVG::Elements::Image,
+    linearGradient: Prawn::SVG::Elements::Gradient,
     title: Prawn::SVG::Elements::Ignored,
     desc: Prawn::SVG::Elements::Ignored,
     metadata: Prawn::SVG::Elements::Ignored,

lib/prawn/svg/elements/base.rb

@@ -124,15 +124,26 @@ def parse_fill_and_stroke_attributes_and_call
       when 'none'
         state[type.to_sym] = false
       else
+        state[type.to_sym] = false
         color_attribute = keyword == 'currentcolor' ? 'color' : type
         color = @attributes[color_attribute]
 
-        begin
-          hex = Prawn::SVG::Color.color_to_hex(color)
-          state[type.to_sym] = true
-          add_call "#{type}_color", hex || '000000'
-        rescue Prawn::SVG::Color::UnresolvableURLWithNoFallbackError
-          state[type.to_sym] = false
+        results = Prawn::SVG::Color.parse(color, document.gradients)
+
+        results.each do |result|
+          case result
+          when Prawn::SVG::Color::Hex
+            state[type.to_sym] = true
+            add_call "#{type}_color", result.value
+            break
+          when Prawn::SVG::Elements::Gradient
+            arguments = result.gradient_arguments(self)
+            if arguments
+              state[type.to_sym] = true
+              add_call "#{type}_gradient", **arguments
+              break
+            end
+          end
         end
       end
 

lib/prawn/svg/elements/gradient.rb

@@ -0,0 +1,117 @@
+class Prawn::SVG::Elements::Gradient < Prawn::SVG::Elements::Base
+  TAG_NAME_TO_TYPE = {"linearGradient" => :linear}
+
+  def parse
+    # A gradient tag without an ID is inaccessible and can never be used
+    raise SkipElementQuietly if attributes['id'].nil?
+
+    assert_compatible_prawn_version
+    load_gradient_configuration
+    load_coordinates
+    load_stops
+
+    document.gradients[attributes['id']] = self
+
+    raise SkipElementQuietly # we don't want anything pushed onto the call stack
+  end
+
+  def gradient_arguments(element)
+    case @units
+    when :bounding_box
+      x1, y1, x2, y2 = element.bounding_box
+      return if y2.nil?
+
+      width = x2 - x1
+      height = y1 - y2
+
+      from = [x1 + width * @x1, y1 - height * @y1]
+      to   = [x1 + width * @x2, y1 - height * @y2]
+
+    when :user_space
+      from = [@x1, @y1]
+      to   = [@x2, @y2]
+    end
+
+    {from: from, to: to, stops: @stops}
+  end
+
+  private
+
+  def type
+    TAG_NAME_TO_TYPE.fetch(name)
+  end
+
+  def assert_compatible_prawn_version
+    if (Prawn::VERSION.split(".").map(&:to_i) <=> [2, 0, 3]) == -1
+      raise SkipElementError, "Prawn 2.0.3+ must be used if you'd like prawn-svg to render gradients"
+    end
+  end
+
+  def load_gradient_configuration
+    @units = attributes["gradientunits"] == 'userSpaceOnUse' ? :user_space : :bounding_box
+
+    if transform = attributes["gradienttransform"]
+      matrix = transform.split(COMMA_WSP_REGEXP).map(&:to_f)
+      if matrix != [1, 0, 0, 1, 0, 0]
+        raise SkipElementError, "prawn-svg does not yet support gradients with a non-identity gradientTransform attribute"
+      end
+    end
+
+    if (spread_method = attributes['spreadmethod']) && spread_method != "pad"
+      warnings << "prawn-svg only currently supports the 'pad' spreadMethod attribute value"
+    end
+  end
+
+  def load_coordinates
+    case @units
+    when :bounding_box
+      @x1 = parse_zero_to_one(attributes["x1"], 0)
+      @y1 = parse_zero_to_one(attributes["y1"], 0)
+      @x2 = parse_zero_to_one(attributes["x2"], 1)
+      @y2 = parse_zero_to_one(attributes["y2"], 0)
+
+    when :user_space
+      @x1 = x(attributes["x1"])
+      @y1 = y(attributes["y1"])
+      @x2 = x(attributes["x2"])
+      @y2 = y(attributes["y2"])
+    end
+  end
+
+  def load_stops
+    stop_elements = source.elements.map do |child|
+      element = Prawn::SVG::Elements::Base.new(document, child, [], {})
+      element.process
+      element
+    end.select do |element|
+      element.name == 'stop' && element.attributes["offset"]
+    end
+
+    @stops = stop_elements.each.with_object([]) do |child, result|
+      offset = parse_zero_to_one(child.attributes["offset"])
+
+      # Offsets must be strictly increasing (SVG 13.2.4)
+      if result.last && result.last.first > offset
+        offset = result.last.first
+      end
+
+      if color_hex = Prawn::SVG::Color.color_to_hex(child.attributes["stop-color"])
+        result << [offset, color_hex]
+      end
+    end
+
+    raise SkipElementError, "gradient does not have any valid stops" if @stops.empty?
+
+    @stops.unshift([0, @stops.first.last]) if @stops.first.first > 0
+    @stops.push([1, @stops.last.last])     if @stops.last.first  < 1
+  end
+
+  def parse_zero_to_one(string, default = 0)
+    string = string.to_s.strip
+    return default if string == ""
+
+    value = string.to_f
+    value /= 100.0 if string[-1..-1] == '%'
+    [0.0, value, 1.0].sort[1]
+  end
+end

spec/prawn/svg/color_spec.rb

@@ -1,7 +1,7 @@
 require File.dirname(__FILE__) + '/../../spec_helper'
 
 describe Prawn::SVG::Color do
-  describe :color_to_hex do
+  describe "::color_to_hex" do
     it "converts #xxx to a hex value" do
       Prawn::SVG::Color.color_to_hex("#9ab").should == "99aabb"
     end
@@ -27,14 +27,35 @@
       expect(Prawn::SVG::Color.color_to_hex("url(#someplace) red")).to eq 'ff0000'
     end
 
-    it "returns nil if the color doesn't exist" do
-      expect(Prawn::SVG::Color.color_to_hex("blurble")).to be nil
+    it "returns black if the color doesn't exist" do
+      expect(Prawn::SVG::Color.color_to_hex("blurble")).to eq '000000'
     end
 
-    it "raises UnresolvableURLWithNoFallbackError if there's no fallback after a url()" do
-      expect {
-        Prawn::SVG::Color.color_to_hex("url(#someplace)")
-      }.to raise_error(Prawn::SVG::Color::UnresolvableURLWithNoFallbackError)
+    it "returns nil if there's no fallback after a url()" do
+      expect(Prawn::SVG::Color.color_to_hex("url(#someplace)")).to be nil
+    end
+  end
+
+  describe "::parse" do
+    let(:gradients) { {"flan" => flan_gradient, "drob" => drob_gradient} }
+    let(:flan_gradient) { double }
+    let(:drob_gradient) { double }
+
+    it "returns a list of all colors parsed, ignoring impossible or non-existent colors" do
+      results = Prawn::SVG::Color.parse("url(#nope) url(#flan) blurble green #123", gradients)
+      expect(results).to eq [
+        flan_gradient,
+        Prawn::SVG::Color::Hex.new("008000"),
+        Prawn::SVG::Color::Hex.new("112233")
+      ]
+    end
+
+    it "appends black to the list if there aren't any url() references" do
+      results = Prawn::SVG::Color.parse("blurble green", gradients)
+      expect(results).to eq [
+        Prawn::SVG::Color::Hex.new("008000"),
+        Prawn::SVG::Color::Hex.new("000000")
+      ]
     end
   end
 end