geometry.rb

def contains_point?(point, poly)
  c = false
  i = -1
  j = poly.size - 1
  while (i += 1) < poly.size
    if ((poly[i][:y] <= point[:y] && point[:y] < poly[j][:y]) || (poly[j][:y] <= point[:y] && point[:y] < poly[i][:y]))
      if (point[:x] < (poly[j][:x] - poly[i][:x]) * (point[:y] - poly[i][:y]) / (poly[j][:y] - poly[i][:y]) + poly[i][:x])
        c = !c
      end
      j = i
    end
  end
  c
end

poly = [
  {x:2, y:0},
  {x:4, y:-2},
  {x:2, y:-4},
  {x:0, y:-2},
]

point1 = {x: 2, y: -2}
point2 = {x: 1, y: 1}
point3 = {x: 1, y: -2}
point4 = {x: 1, y: -1}

puts contains_point?(point1, poly)
puts contains_point?(point2, poly)
puts contains_point?(point3, poly)
puts contains_point?(point4, poly)