# Returns the three vertices of the given triangle in CCW order
GetVertices(t)
# Returns the three triangles adjacent to this one.
# Ordered so that GetAdjacentTriangles(t)[i] shares entries i and i+1 of GetVertices(t).
# An entry may be None if the edge is on the boundary of the navmesh.
GetAdjacentTriangles(t)

def LineOfSight(s1,t1,s2,t2):
  d = s2 - s1 # Direction from s1 to s2
  n = (-d.y, d.x) # Normal to line s1-s2.
  ns = Dot(n, s1)
  while t1 != t2:
    dp = [Dot(n, v) for v in navmesh.GetVertices(t1)]
    for i in xrange(3):
      if dp[i] < 0 and dp[(i+1)%3] >= 0: break
    # We should cross the edge between vertices i and i+1.
    t1 = navmesh.GetAdjacentTriangles(t1)[i]
    if t1 is None: return False # We stepped off the NavMesh
  return True