From 93d1af38c2b2bed900c45eeab98739312882defb Mon Sep 17 00:00:00 2001
From: Mog Nesbitt <mog@seriousorange.com>
Date: Sun, 28 Jan 2024 11:03:02 +1300
Subject: [PATCH] Correctly handle "use"ing symbols

The svg spec says to treat "use"d symbols as svg elements, and to
transfer the width and height from the use element to the cloned svg
element.  This fixes a rendering problem reported in issue #157.
---
 lib/prawn/svg/elements/use.rb | 32 ++++++++++++++++++++------------
 spec/sample_svg/symbol.svg    | 12 ++++++++++++
 2 files changed, 32 insertions(+), 12 deletions(-)
 create mode 100644 spec/sample_svg/symbol.svg

diff --git a/lib/prawn/svg/elements/use.rb b/lib/prawn/svg/elements/use.rb
index ea14be0..36221f2 100644
--- a/lib/prawn/svg/elements/use.rb
+++ b/lib/prawn/svg/elements/use.rb
@@ -1,15 +1,12 @@
 class Prawn::SVG::Elements::Use < Prawn::SVG::Elements::Base
-  attr_reader :referenced_element_class
-  attr_reader :referenced_element_source
+  attr_reader :referenced_element_class, :referenced_element_source
 
   def parse
     href = href_attribute
-    if href.nil?
-      raise SkipElementError, "use tag must have an href or xlink:href"
-    end
+    raise SkipElementError, 'use tag must have an href or xlink:href' if href.nil?
 
     if href[0..0] != '#'
-      raise SkipElementError, "use tag has an href that is not a reference to an id; this is not supported"
+      raise SkipElementError, 'use tag has an href that is not a reference to an id; this is not supported'
     end
 
     id = href[1..-1]
@@ -29,14 +26,18 @@ def parse
       end
     end
 
-    if referenced_element_class.nil?
-      raise SkipElementError, "no tag with ID '#{id}' was found, referenced by use tag"
+    raise SkipElementError, "no tag with ID '#{id}' was found, referenced by use tag" if referenced_element_class.nil?
+
+    if referenced_element_source.name == 'symbol'
+      @referenced_element_class = Prawn::SVG::Elements::Viewport
     end
 
     state.inside_use = true
 
     @x = attributes['x']
     @y = attributes['y']
+    @width = attributes['width']
+    @height = attributes['height']
   end
 
   def container?
@@ -45,16 +46,23 @@ def container?
 
   def apply
     if @x || @y
-      add_call_and_enter "translate", x_pixels(@x || 0), -y_pixels(@y || 0)
+      add_call_and_enter 'translate', x_pixels(@x || 0), -y_pixels(@y || 0)
     end
   end
 
   def process_child_elements
-    add_call "save"
+    add_call 'save'
+
+    source = referenced_element_source.dup
+
+    if referenced_element_class == Prawn::SVG::Elements::Viewport
+      source.attributes['width'] = @width || '100%'
+      source.attributes['height'] = @height || '100%'
+    end
 
-    child = referenced_element_class.new(document, referenced_element_source, calls, state.dup)
+    child = referenced_element_class.new(document, source, calls, state.dup)
     child.process
 
-    add_call "restore"
+    add_call 'restore'
   end
 end
diff --git a/spec/sample_svg/symbol.svg b/spec/sample_svg/symbol.svg
new file mode 100644
index 0000000..33eb7aa
--- /dev/null
+++ b/spec/sample_svg/symbol.svg
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg viewBox="0 0 1000 1000" xmlns="http://www.w3.org/2000/svg" xmlns:xlink='http://www.w3.org/1999/xlink' version="1.1">
+  <symbol id="rects" viewBox="0 0 100 100">
+    <rect x="10" y="10" width="80" height="80" fill="none" stroke="red"/>
+    <rect x="20" y="20" width="60" height="60" fill="none" stroke="green"/>
+    <rect x="30" y="30" width="40" height="40" fill="none" stroke="blue"/>
+  </symbol>
+  <rect width="1000" height="1000" fill="none" stroke="black"/>
+  <use x="100" y="100" width="800" height="800" xlink:href="#rects"/>
+  <use x="400" y="400" width="200" height="200" xlink:href="#rects"/>
+</svg>
\ No newline at end of file