Houdini 11 Review: Flipping the Switch
This new automatic method of fracturing geometry for rigid body simulations is even wrapped up in a handy little shelf tool named "Make Breakable," which works in conjunction with the "RBD Object" shelf tool to set up your geometry in a dynamics network with fully automatic fracturing within three or four mouse clicks.
Although there is no doubt that the Make Breakable tool will save artists time, my main concern with this approach, and it seems Side Effects would agree with this based on the comments in the tools documentation, is that the amount of user control when using this option is reduced. Yes, this tool does fracture geometry in a physically "correct" manner, but what is correct on many occasions is simply not what the client wants. They will have their own carefully crafted vision for a destruction money-shot that will not be compromised by over analyzing what is physically accurate.
The user is presented with a number of options on the Voronoi Fracture Configure object DOP, the node that is central to the network created by the Make Breakable shelf tool (along with the activation of the Voronoi Fracture Solver, which is now contained within the RBD solver). One of the most useful is the "Maximum fractures" option, which allows the user to specify how many times each fractured "piece" will re-fracture on further impact with any other rigid bodies. This can dramatically change the look and feel of a simulation. The user also has control over the points scattered over the geometry surface which determine the density of individual pieces that will be created on shattering, from large chunks to pieces of small fragmented debris. Controls are also available for clustering shattered pieces.
All of these parameters make auto-fracturing more appealing and flexible, but an artist may get into a tricky situation if using auto-fracturing and is then given a specific piece of art direction, which is simply not facilitated by how the object falls or is hit. Overall, the tool is technically very impressive, with the potential to make certain tasks much quicker and easier (such as mid and background destruction as mentioned) and is a very welcome addition to the RBD toolset. For users that wish to forgo the automatic method for more control, the "Shatter" shelf tool, introduced in Houdini 10, employs the Voronoi Fracture sop and is a very capable and fast method of pre-fracture. The use of this tool allows the user to explicitly control the positioning and bias of fracture points using any method they wish from the extensive SOP (surface operators) tool-set. The best of both worlds, one might say.