Как определить наличие точки внутри полигона?

Можно через pillow. Как-то так:

import pygame, PIL.Image
pygame.init()

def collidepointInPolygon(point_pos, polygon_pos):
    start = time.time()
    a = pygame.Surface(size=(point_pos[0] + 1, point_pos[1] + 1))
    a.fill((0, 0, 0))
    pygame.draw.polygon(a, (255, 255, 255), polygon_pos)
    a = pygame.image.tostring(a, "RGB")
    a = PIL.Image.frombytes("RGB", (point_pos[0] + 1, point_pos[1] + 1), a)
    a = a.getpixel((point_pos[0], point_pos[1])) == (255, 255, 255)
    
    return a

collidepointInPolygon([0, 0], [[100, 100], [200, 200], [200, 100]])