Point in polygon is difficult in GIS because the polygon can have a very large number of verticies that all have to be checked. Does a GPU have sufficient bandwidth to load large polygons quickly? Do GPU's have to sample each vertex every time?
Often the best way is to divide polygons into tiles that have a limited number of verticies (this also makes indexing much more effective).
Often the best way is to divide polygons into tiles that have a limited number of verticies (this also makes indexing much more effective).