polyzone.lua

--[[
polyzone.lua

Lua implementation of winding number algorithm to determine whether a point is inside a polygon
Credits:

https://gist.github.com/vlasky/d0d1d97af30af3191fc214beaf379acc - Public wn_PnPoly js conversion
http://geomalgorithms.com/a03-_inclusion.html - Original wn_PnPoly function
--]]

local function isLeft(p0,p1,p2)
  return ( ( (p1.x - p0.x) * (p2.y - p0.y) ) - ( (p2.x - p0.x) * (p1.y - p0.y) ) )
end

local polyzoneMt = {}
polyzoneMt.__index = polyzoneMt

function polyzoneMt:isPointInside(point)
  if point.z then
    if point.z > self.maxZ 
    or point.z < self.minZ
    then
      return false
    end
  end

  local vs = self.points
  local wn = 0

  for i=1,#self.points,1 do
    local v1 = vs[i]
    local v2 = vs[i == #self.points and 1 or i+1]

    if v2.y <= point.y then
      if v1.y > point.y then
        if isLeft(v2,v1,point) > 0 then
          wn = wn + 1
        end
      end
    else
      if v1.y <= point.y then
        if isLeft(v2,v1,point) < 0 then
          wn = wn - 1
        end
      end
    end
  end

  return (wn ~= 0)
end

function polyzoneMt:destroy()
  self = nil
end

Polyzone = {}

Polyzone.New = function(points,minZ,maxZ)
  return setmetatable({
    points  = points,
    minZ    = minZ or -1,
    maxZ    = maxZ or 1
  },polyzoneMt)
end

--[[
Complex polygon example

local points = {
  {x =  2, y =  2},
  {x = -2, y =  0},
  {x =  2, y = -2},
  {x = -2, y = -2},
  {x = -2, y =  2}
}

local comparePoint = {x = 1, y = 1}

local pz = Polyzone.New(points)

print( pz:isPointInside(comparePoint) )
--]]