Repository: ManimCommunity/manim
File: manim/mobject/opengl/opengl_surface.py (Python)

Code before:
        # this is called.
        nu, nv = self.resolution
        if nu == 0 or nv == 0:
            self.triangle_indices = np.zeros(0, dtype=int)
            return
        index_grid = np.arange(nu * nv).reshape((nu, nv))
        indices = np.zeros(6 * (nu - 1) * (nv - 1), dtype=int)
        indices[0::6] = index_grid[:-1, :-1].flatten()  # Top left
        indices[1::6] = index_grid[+1:, :-1].flatten()  # Bottom left
        indices[2::6] = index_grid[:-1, +1:].flatten()  # Top right
        indices[3::6] = index_grid[:-1, +1:].flatten()  # Top right
        indices[4::6] = index_grid[+1:, :-1].flatten()  # Bottom left
        indices[5::6] = index_grid[+1:, +1:].flatten()  # Bottom right
        self.triangle_indices = indices

    def get_triangle_indices(self):
        return self.triangle_indices

    def get_surface_points_and_nudged_points(
        self,
    ) -> tuple[MatrixMN, MatrixMN, MatrixMN]:
        points = self.points
        k = len(points) // 3
        return points[:k], points[k : 2 * k], points[2 * k :]

    def get_unit_normals(self) -> MatrixMN:
        s_points, du_points, dv_points = self.get_surface_points_and_nudged_points()
        normals = np.cross(
            (du_points - s_points) / self.epsilon,
            (dv_points - s_points) / self.epsilon,
        )
        return normalize_along_axis(normals, 1)

    def pointwise_become_partial(self, smobject, a, b, axis=None):
        assert isinstance(smobject, OpenGLSurface)
        if axis is None:
            axis = self.prefered_creation_axis
        if a <= 0 and b >= 1:
            self.match_points(smobject)
            return self

        nu, nv = smobject.resolution
        self.set_points(
            np.vstack(
                [
                    self.get_partial_points_array(
                        arr.copy(),
                        a,
                        b,
                        (nu, nv, 3),
                        axis=axis,

Review comment (suggestion):
Since the returned unit normals are vectors:
```suggestion
    def get_unit_normals(self) -> Vector3D_Array:
```

Code after:
        # this is called.
        nu, nv = self.resolution
        if nu == 0 or nv == 0:
            self.triangle_indices = np.zeros(0, dtype=int)
            return
        index_grid = np.arange(nu * nv).reshape((nu, nv))
        indices = np.zeros(6 * (nu - 1) * (nv - 1), dtype=int)
        indices[0::6] = index_grid[:-1, :-1].flatten()  # Top left
        indices[1::6] = index_grid[+1:, :-1].flatten()  # Bottom left
        indices[2::6] = index_grid[:-1, +1:].flatten()  # Top right
        indices[3::6] = index_grid[:-1, +1:].flatten()  # Top right
        indices[4::6] = index_grid[+1:, :-1].flatten()  # Bottom left
        indices[5::6] = index_grid[+1:, +1:].flatten()  # Bottom right
        self.triangle_indices = indices

    def get_triangle_indices(self):
        return self.triangle_indices

    def get_surface_points_and_nudged_points(
        self,
    ) -> tuple[Point3D_Array, Point3D_Array, Point3D_Array]:
        points = self.points
        k = len(points) // 3
        return points[:k], points[k : 2 * k], points[2 * k :]

    def get_unit_normals(self) -> Vector3D_Array:
        s_points, du_points, dv_points = self.get_surface_points_and_nudged_points()
        normals = np.cross(
            (du_points - s_points) / self.epsilon,
            (dv_points - s_points) / self.epsilon,
        )
        return normalize_along_axis(normals, 1)

    def pointwise_become_partial(self, smobject, a, b, axis=None):
        assert isinstance(smobject, OpenGLSurface)
        if axis is None:
            axis = self.prefered_creation_axis
        if a <= 0 and b >= 1:
            self.match_points(smobject)
            return self

        nu, nv = smobject.resolution
        self.set_points(
            np.vstack(
                [
                    self.get_partial_points_array(
                        arr.copy(),
                        a,
                        b,
                        (nu, nv, 3),
                        axis=axis,