#==============================================================================
# * Class Bitmap
#==============================================================================
class Bitmap
  def draw_line(x1,y1,x2,y2,c = Color.new(0,0,0,255))
    # Vertical line
    if x1 == x2
      for y in y1...y2
        self.set_pixel(x1,y,c)
      end
    # Horizontal line
    elsif y1 == y2
      for x in x1...x2
        self.set_pixel(x,y1,c)
      end
    # point
    elsif x1 == x2 and y1 == y2
      self.set_pixel(x1,y1,c)
    # Neither horizontal or vertical
    else
      # Function for line (f(x) = mx + n)
      m = (y2-y1)/(x2-x1).to_f # gradient
      # Prevent zerodivision
      if x1 != 0
        n = y1/(m*x1) # base
      elsif x2 != 0
        n = y2/(m*x2) # base
      end
      # set_pixel(x,f(x)) for every x between x1 and x2
      for x in x1...x2
        self.set_pixel(x,m*x+n,c)
      end
    end
  end  
end