polypoint

Polygon Point Collision Detection

here is the original love2d forum thread: [1]

here is the original source website, beware its written in C++ [2]

The code below is a function that is called to return true when a point is within the vertices of a polygon and false otherwise. The math used is the Jordan Curve Theorem --> [3]

---

[[:Lua:: function polyPoint(vertices,px,py) local collision = false local next = 1

 for current = 1, #vertices do
   next = current + 1
   if (next > #vertices) then
     next = 1
   end
   local vc = vertices[current]
   local vn = vertices[next]
   if (((vc.y >= py and vn.y < py) or (vc.y < py and vn.y >= py)) and
   (px < (vn.x-vc.x)*(py-vc.y) / (vn.y-vc.y)+vc.x)) then
       collision = not(collision)
   end
 end
 return collision

end ]]

Note: The code assumes your polygon vertices are stored in a table with tuples or pairs of x and y like this.

[[:Lua:: v = {} v[1] = {x = 200,y = 100} v[2] = {x = 400,y = 130} v[3] = {x = 350,y = 300} v[4] = {x = 250,y = 300} ]]

You can find the .love here for an example. Love Version 11.3 [4]