T vgl_triangle_test_discriminant(T x1, T y1, T x2, T y2, T x3, T y3)
Compute discriminant function.
bool vgl_triangle_test_inside(T x1, T y1, T x2, T y2, T x3, T y3, T x, T y)
Function returns true if (x, y) is inside, or on the boundary of triangle.