Breaking Only Part of Whole

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How does one break only part of the Whole using Voronoi? I've scattered points on a specific side but the voronoi still breaks all of the geo. You know, like when a massive object is hit, pieces of it break off, but NOT the whole thing.

Is Voronoi useful for that or do I have to go a different route?

Also, on a different project, I have used the ‘break’ sop to cut some pieces in a torus followed by an “assemble” sop. When I drop the torus onto a floor it breaks apart using the RBD…. Problem is some pieces fly THROUGH the torus on impact, instead of projecting only on the outside… as would be the case in a real impact.

So basically the pieces imagine you have some M&Ms embedded on top of a doughnut… if you drop it, the M&Ms will fly outwards due to the shock of the doughnut hitting the floor… Some of mine do, but some pass through the doughnut and hit the floor. I'm guessing it's some tolerance issue. Any help as to where I should look would be appreciated.

Thank You….
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You can use voronoi for that. What you could do is separate the geo from each other by just creating two meshes (just use the delete sop) and use one as a static and the other as a dynamic object and just fracture the last one. Also by using for example a sphere as the input for your voronoi fracture points, you can turn on Cluster Pieces and that should give you a lot of shards for the area where the sphere is placed and one big chunk for the rest (all are dynamic objects)

Using glue network constraints and then transferring a new strength to it (attribute transfer in the glue dop that transfers a glue strength that is low enough to break the bonds and thus create the breaking) gives you more control over where and when exactly the breaking occurs.

I think some of this is explained in this bullet tutorial https://vimeo.com/56916407 [vimeo.com] and I'm pretty sure there is also a good Digital Tutors tutorial about it, if you need it.

About the other project.. have you tried applying an extra velocity to the pieces that makes sure they are heading in the right direction? Not sure if this would actually give you the effect you want but that's all I can come up with at the moment
showreel: https://vimeo.com/79698203 [vimeo.com]
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Indeed there is a great tutorial who can answer some of your questions :
http://www.digitaltutors.com/tutorial/1091-Controlling-Your-Fractures-in-Houdini [digitaltutors.com]
https://vimeo.com/obreadytom [vimeo.com]
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