Add ellipse method

Also experimenting with using stroke_preserve, which in turn may make the other methods less repetitive.

Closes #66

lib/squib/api/shapes.rb

@@ -59,6 +59,34 @@ module Squib
       end
     end
 
+     # Draw an ellipse
+    #
+    # @example
+    #   ellipse x: 0, y: 0, width: 825, height: 1125
+    #
+    # Options support Arrays, see {file:README.md#Arrays_and_Singleton_Expansion Arrays and Singleon Expansion}
+    #
+    # @option opts range [Enumerable, :all] (:all) the range of cards over which this will be rendered. See {file:README.md#Specifying_Ranges Specifying Ranges}
+    # @option opts x [Integer] (0) the x-coordinate to place. Supports Unit Conversion, see {file:README.md#Units Units}.
+    # @option opts y [Integer] (0) the y-coordinate to place. Supports Unit Conversion, see {file:README.md#Units Units}.
+    # @option opts width [Integer] the width of the rectangle. Supports Unit Conversion, see {file:README.md#Units Units}.
+    # @option opts height [Integer] the height of the rectangle. Supports Unit Conversion, see {file:README.md#Units Units}.
+    # @option opts fill_color [String] ('#0000') the color with which to fill the rectangle. See {file:README.md#Specifying_Colors___Gradients Specifying Colors & Gradients}
+    # @option opts stroke_color [String] (:black) the color with which to stroke the outside of the rectangle. {file:README.md#Specifying_Colors___Gradients Specifying Colors & Gradients}
+    # @option opts stroke_width [Decimal] (2.0) the width of the outside stroke. Supports Unit Conversion, see {file:README.md#Units Units}.
+    # @option opts layout [String, Symbol] (nil) entry in the layout to use as defaults for this command. See {file:README.md#Custom_Layouts Custom Layouts}
+    # @return [nil] intended to be void
+    # @api public
+    def ellipse(opts = {})
+      opts = needs(opts, [:range, :x, :y, :width, :height,
+                          :fill_color, :stroke_color, :stroke_width, :layout])
+      opts[:range].each do |i|
+        @cards[i].ellipse(opts[:x][i], opts[:y][i], opts[:width][i], opts[:height][i],
+                          opts[:fill_color][i], opts[:stroke_color][i],
+                          opts[:stroke_width][i])
+      end
+    end
+
     # Draw a triangle using the given coordinates
     #
     # @example

lib/squib/graphics/cairo_context_wrapper.rb

@@ -22,7 +22,8 @@ module Squib
         :show_pango_layout, :rounded_rectangle, :set_line_width, :stroke, :fill,
         :set_source, :scale, :render_rsvg_handle, :circle, :triangle, :line_to,
         :operator=, :show_page, :clip, :transform, :mask, :create_pango_layout,
-        :antialias=, :curve_to, :matrix, :matrix=, :identity_matrix, :pango_layout_path
+        :antialias=, :curve_to, :matrix, :matrix=, :identity_matrix, :pango_layout_path,
+        :stroke_preserve
 
       # :nodoc:
       # @api private

lib/squib/graphics/shapes.rb

@@ -32,6 +32,34 @@ module Squib
       end
     end
 
+    # Ellipse drawing taken from looking at the control points in Inkscape
+    # Think of it like a rectangle. Curves go from mid-points of the sides
+    # of the rectangle. Control points are at 1/4 and 3/4 of the side.
+    # :nodoc:
+    # @api private
+    def ellipse(x, y, w, h, fill_color, stroke_color, stroke_width)
+      use_cairo do |cc|
+        cc.move_to(x, y + 0.5*h)       # start west
+        cc.curve_to(x, y + 0.25*h,     # west to north
+                    x + 0.25*w, y,
+                    x +  0.5*w, y)
+        cc.curve_to(x + 0.75*w, y,     # north to east
+                    x + w, y + 0.25*h,
+                    x + w, y + 0.5*h)
+        cc.curve_to(x + w, y + 0.75*h, # east to south
+                    x + 0.75*w, y + h,
+                    x + 0.5*w, y + h)
+        cc.curve_to(x + 0.25*w, y + h, # south to west
+                    x, y + 0.75*h,
+                    x, y + 0.5*h)
+        cc.set_source_squibcolor(stroke_color)
+        cc.set_line_width(stroke_width)
+        cc.stroke_preserve
+        cc.set_source_squibcolor(fill_color)
+        cc.fill
+      end
+    end
+
     # :nodoc:
     # @api private
     def triangle(x1, y1, x2, y2, x3, y3, fill_color, stroke_color, stroke_width)