Create an (X, Y) plane suitable for graphing equations in Ruby.

graph.rb

require "rubygems"
require 'png'

class RubyGraph
    attr_accessor :x_precision
    attr_accessor :y_precision
    attr_accessor :x_pos_units
    attr_accessor :y_pos_units
    attr_accessor :x_neg_units
    attr_accessor :y_neg_units

    def initialize
        @x_precision = 1
        @y_precision = 1
        @x_pos_units = 200
        @y_pos_units = 200
        @x_neg_units = 200
        @y_neg_units = 200
    end

    def fn x
        x
    end

    def graph
        x_start = -1 * @x_neg_units;
        x_end = @x_pos_units;
        y_start = -1 * @y_neg_units;
        y_end = @y_pos_units;
        canvas = PNG::Canvas.new(@x_pos_units + @x_neg_units + 1, @y_pos_units + @y_neg_units + 1);
        x_start.upto(x_end) do |x|
            y_start.upto(y_end) do |y|
                # 255:white 0:black
                r = g = b = x == 0 || y == 0 ? 0 : 255
                if y == fn(x)
                    r = 255
                    g = 0
                    b = 0
                end
                canvas[x + @x_neg_units, y + @y_neg_units] = PNG::Color.new(r, g, b)
            end
        end
        png = PNG.new(canvas)
        png.save("graph.png")
    end
end

rg = RubyGraph.new
rg.graph