A dot generator for math education

hexdot-generator.rb

#!/usr/bin/env ruby

# hexdot-generator.rb : A dot generator for math education
#   by takehikom
# see also: https://takehikom.hateblo.jp/entry/2021/04/25/082407

class HexdotGenerator
  def initialize(opt = {})
    @filename = opt[:file] || "hexdot.svg"
    setup
  end

  def setup
    @row = 3
    @col = 8
    @radius = 8
    @distance = @radius * 6
    @margin = @radius * 4
    @image_width = (@margin * 2 + @distance * (@col - 1)).to_i
    @image_height = (@margin * 2 + @distance * Math.sqrt(3.0) * 0.5 * (@row - 1)).to_i
    @io = nil
  end
  attr_reader :row, :col, :radius
  attr_reader :distance, :margin
  attr_reader :image_width, :image_height
  attr_reader :io

  def coord(x, y)
    x_coord = @margin + @distance * x
    x_coord += @distance * 0.5 if y.odd?
    y_coord = @margin + @distance * Math.sqrt(3.0) * 0.5 * y
    [x_coord, y_coord]
  end

  def start(&block_draw)
    @io = open(@filename, "w")
    @io.puts('<svg xmlns="http://www.w3.org/2000/svg" width="%dpx" height="%dpx">' % [@image_width, @image_height])
    @io.puts('<rect x="0" y="0" width="%d" height="%d" fill="#f0fff0"/>' % [@image_width, @image_height])

    if block_given?
      block_draw.call(self)
    end

    @row.times do |y|
      (y.even? ? @col : (@col - 1)).times do |x|
        x_coord, y_coord = coord(x, y)
        # $stderr.puts("DEBUG: x=#{x}, y=#{y}, x_coord=#{x_coord}, y_coord=#{y_coord}")
        @io.puts('<circle cx="%f" cy="%f" r="%f" fill="black" stroke="none"/>' % [x_coord, y_coord, @radius])
      end
    end

    @io.puts('</svg>')
    @io.close
    @io = nil

    self
  end
end

if __FILE__ == $0
  HexdotGenerator.new(file: "hexdot0.svg").start

  HexdotGenerator.new(file: "hexdot1.svg").start do |h_o|
    h_o.row.times do |y1|
      x1 = 0
      # y1 = 0
      x2 = h_o.col - 1 - (y1.odd? ? 1 : 0)
      y2 = y1
      x1_coord, y1_coord = h_o.send(:coord, x1, y1)
      x2_coord, y2_coord = h_o.send(:coord, x2, y2)
      stroke_color = ["red", "green", "blue"][y1 % 3]
      stroke_width = h_o.radius * 0.33
      h_o.io.puts('<line x1="%f" y1="%f" x2="%f" y2="%f" stroke="%s" stroke-width="%f"/>' % [x1_coord, y1_coord, x2_coord, y2_coord, stroke_color, stroke_width])
    end
  end

  HexdotGenerator.new(file: "hexdot2.svg").start do |h_o|
    # It will be wrong if h_o.row != 3
    h_o.col.times do |x1|
      y1 = 0
      x2 = x1
      y2 = h_o.row - 1
      x1_coord, y1_coord = h_o.send(:coord, x1, y1)
      x2_coord, y2_coord = h_o.send(:coord, x2, y2)
      stroke_color = "blue"
      stroke_width = h_o.radius * 0.33
      h_o.io.puts('<line x1="%f" y1="%f" x2="%f" y2="%f" stroke="%s" stroke-width="%f"/>' % [x1_coord, y1_coord, x2_coord, y2_coord, stroke_color, stroke_width])
    end

    x1 = 0
    y1 = 1
    x2 = h_o.col - 2
    y2 = y1
    x1_coord, y1_coord = h_o.send(:coord, x1, y1)
    x2_coord, y2_coord = h_o.send(:coord, x2, y2)
    stroke_color = "green"
    stroke_width = h_o.radius * 0.33
    h_o.io.puts('<line x1="%f" y1="%f" x2="%f" y2="%f" stroke="%s" stroke-width="%f"/>' % [x1_coord, y1_coord, x2_coord, y2_coord, stroke_color, stroke_width])
  end

  HexdotGenerator.new(file: "hexdot3.svg").start do |h_o|
    1.upto(h_o.col - 1) do |x1|
      coord_a = []
      h_o.row.times do |y1|
        x = x1 - (y1.odd? ? 1 : 0)
        y = y1
        x_coord, y_coord = h_o.send(:coord, x, y)
        coord_a << x_coord << y_coord
      end
      stroke_color = "blue"
      stroke_width = h_o.radius * 0.33
      h_o.io.puts('<polyline points="%s" stroke="%s" stroke-width="%f" fill="none"/>' % [coord_a.join(','), stroke_color, stroke_width])
    end
  end

  HexdotGenerator.new(file: "hexdot4.svg").start do |h_o|
    h_o.col.times do |x1|
      next if x1.odd?
      next if x1 + 2 >= h_o.col

      coord_a = []
      h_o.row.times do |y1|
        x = x1
        y = y1
        x_coord, y_coord = h_o.send(:coord, x, y)
        coord_a << x_coord << y_coord
      end
      (h_o.row - 1).downto(0) do |y1|
        x = x1 + 1
        y = y1
        x_coord, y_coord = h_o.send(:coord, x, y)
        coord_a << x_coord << y_coord
      end
      stroke_color = "red"
      stroke_width = h_o.radius * 0.33
      h_o.io.puts('<polygon points="%s" stroke="%s" stroke-width="%f" fill="none"/>' % [coord_a.join(','), stroke_color, stroke_width])
    end

    if h_o.col.even?
      x1 = h_o.col - 2
      coord_a = []
      h_o.row.times do |y1|
        x = x1
        y = y1
        x_coord, y_coord = h_o.send(:coord, x, y)
        coord_a << x_coord << y_coord
      end
      (h_o.row - 1).downto(0) do |y1|
        x = x1 + 1 - (y1.odd? ? 1 : 0)
        y = y1
        x_coord, y_coord = h_o.send(:coord, x, y)
        coord_a << x_coord << y_coord
      end
      stroke_color = "blue"
      stroke_width = h_o.radius * 0.33
      h_o.io.puts('<polygon points="%s" stroke="%s" stroke-width="%f" fill="none"/>' % [coord_a.join(','), stroke_color, stroke_width])
    end
  end
end