Support middle function of dominant-baseline for <text>

README.md

@@ -62,7 +62,7 @@ prawn-svg supports most but not all of the full SVG 1.1 specification.  It curre
    implementation of elliptical arc is a bit rough at the moment.
 
  - `<text>`, `<tspan>` and `<tref>` with attributes `x`, `y`, `dx`, `dy`, `rotate`, 'textLength', 'lengthAdjust', and with extra properties
-   `text-anchor`, `text-decoration` (underline only), `font-size`, `font-family`, `font-weight`, `font-style`, `letter-spacing`
+   `text-anchor`, `text-decoration` (underline only), `font-size`, `font-family`, `font-weight`, `font-style`, `letter-spacing`, `dominant-baseline` (middle only)
 
  - <tt>&lt;svg&gt;</tt>, <tt>&lt;g&gt;</tt> and <tt>&lt;symbol&gt;</tt>
 

lib/prawn/svg/elements/text_component.rb

@@ -41,12 +41,13 @@ def apply
     font = select_font
     apply_font(font) if font
 
-    # text_anchor isn't a Prawn option; we have to do some math to support it
-    # and so we handle this in Prawn::SVG::Interface#rewrite_call_arguments
+    # text_anchor and dominant_baseline aren't Prawn options; we have to do some math to support them
+    # and so we handle them in Prawn::SVG::Interface#rewrite_call_arguments
     opts = {
       size:        computed_properties.numerical_font_size,
       style:       font && font.subfamily,
       text_anchor: computed_properties.text_anchor,
+      dominant_baseline: computed_properties.dominant_baseline,
     }
 
     opts[:decoration] = computed_properties.text_decoration unless computed_properties.text_decoration == 'none'

lib/prawn/svg/interface.rb

@@ -149,6 +149,13 @@ def rewrite_call_arguments(prawn, call, arguments, kwarguments)
           at[0] = @cursor[0] if at[0] == :relative
           at[1] = @cursor[1] if at[1] == :relative
 
+          case options.delete(:dominant_baseline)
+          when 'middle'
+            height = prawn.font.height
+            at[1] -= height / 2.0
+            @cursor = [at[0], at[1]]
+          end
+
           if offset = options.delete(:offset)
             at[0] += offset[0]
             at[1] -= offset[1]

lib/prawn/svg/properties.rb

@@ -38,6 +38,7 @@ class Prawn::SVG::Properties
     "stroke-width"     => Config.new("1", true),
     "text-anchor"      => Config.new("start", true, %w(inherit start middle end), true),
     'text-decoration'  => Config.new('none', true, %w(inherit none underline), true),
+    "dominant-baseline" => Config.new("auto", true, %w(inherit auto middle), true),
   }.freeze
 
   PROPERTIES.each do |name, value|