The effect: Pieces break apart according to a bunch of paths, on an object that is moving/deforming. In parts, we have to: (1) Fracture the sphere according to some paths. (2) Have the pieces start out as part of the keyframed animation e.g. as part of the spinning globe, and then switch over to being simulated by the RBD Solver when some “trigger” happens. @active and @deforming We learned previously, the RBD Solver looks for the attribute i@active on the pieces to determine whether they are “reactive” in a sim.

Point Deform lets us transfer animation to any mesh (within reason) with just a buncha points. Lets create this contrived example, using this static mesh: And this animated “point cloud”: Wiring them up: For the second input, we use a TimeShift to hold the first frame of the point cloud animation, which gives us the “rest lattice” that matches the static mesh’s topology (ideally). All this essentially animates the mesh:

We start with two vectors @N (yellow) – which is the primitive’s normal from a Normals SOP, and {0,1,0} – the global up (gray). When the primitive is not rotated, these two vectors are parallel. By using a buncha cross, we can derive our main axes: vector pink = cross(@N, {0, 1, 0}); // First cross product vector green = cross(pink, @N); // Second cross product, the "double cross" Note 1: The green vector is essentially an “up-ish” vector that is always parallel to the plane and never points downwards.