prawnpdf/prawn

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manual/graphics/fill_rules.rb

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# frozen_string_literal: true

# Prawn's fill operators (<code>fill</code> and <code>fill_and_stroke</code>
# both accept a <code>:fill_rule</code> option. These rules determine which
# parts of the page are counted as "inside" vs. "outside" the path. There are
# two fill rules:
#
# * <code>:nonzero_winding_number</code> (default): a point is inside the path
# if a ray from that point to infinity crosses a nonzero "net number" of path
# segments, where path segments intersecting in one direction are counted as
# positive and those in the other direction negative.
#
# * <code>:even_odd</code>: A point is inside the path if a ray from that point
# to infinity crosses an odd number of path segments, regardless of direction.
#
# The differences between the fill rules only come into play with complex
# paths; they are identical for simple shapes.

require_relative '../example_helper'

filename = File.basename(__FILE__).gsub('.rb', '.pdf')
Prawn::ManualBuilder::Example.generate(filename) do
  pentagram = [[181, 95], [0, 36], [111, 190], [111, 0], [0, 154]]

  stroke_color 'ff0000'
  line_width 2

  text_box 'Nonzero Winding Number', at: [50, 215],
                                     width: 170,
                                     align: :center
  polygon(*pentagram.map { |x, y| [x + 50, y] })
  fill_and_stroke

  text_box 'Even-Odd', at: [330, 215], width: 170, align: :center
  polygon(*pentagram.map { |x, y| [x + 330, y] })
  fill_and_stroke(fill_rule: :even_odd)
end