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Fracture Control


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Hello Everyone,

Since this is my first post here please let me introduce myself.

My name is Adrian Lazar, I'm a 3d artist (generalist) using Softimage - some of my work can be viewed here: http://vimeo.com/channels/adrianlazar3d

A couple of months ago I started learning Houdini - tutorials from sidefx.com, Peter Quint's videos on Vimeo and also just browsing OdForce and the community from the official website.

It was a slow start and I wanted to quit many times but somehow each time I went back to Houdini... is quite addictive :)

I'm interested to learn as much as I can in all areas of Houdini but at the end I'll focus on shaders and lighting and hopefully modelling. I say hopefully because at least for me modelling is the hardest part to learn in a new package especially since I find the modelling work-flow from softimage almost perfect :) Of course it's a vey subjective opinion.

Anyway... today I was playing with dynamics and I tried to break a column using the voronoi fracture, similar to the tutorial from go procedural. The difference is that my column should be stuck to the ground (like a subway pillar) but when the simulation runs it doesn't act that way. Maybe I can paint the points that I don't want to fracture at all? Like I can paint the bottom of the pillar so it doesn't move or fracture.

I think that a picture will describe better what I mean,




Edited by AdrianLazar
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Hi Adrian, and welcome.

From the top of my mind, you got two quick ways to do this:

- add a Pin Constrain to the pieces at the base so that they don´t move. That will give you the motion you are after. I have tried this myself and it works perfectly. It´s a bit uncomfortable if there are many pieces, but you usually get this done in about 5 minutes.

- Rename the base pieces to something else, so that they don´t get put into the group mask of the RBD Glue Object. Haven´t tried this myself, but it should work...(at least, it does in my mind)

Hope this helps.

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If you want to constrain multiple piece to the floor... the way the voronoi fracture sop works is pretty convenient. Each seed point number will be mapped to the piece group number. All you have to do is know which points need to be constrained... maybe you can apply an attribute called "on" if $TY < 0.1 or something like that.

Once you have that group number, you can use a combination of rbd pin constraint and apply relationship. Since the apply relationship node allows you to use a stamp expression in objects connected to its second(green) input, you can use an expression in the constraint activation like...

point("/obj/fracturedobject/OUT_ON_ATTR", stamp("../applyrel1", "AFFECTORID", 0), "on", 0)

I recommend taking the time to look through this forum if you want to learn about the wonders of the apply relationship node.


Edited by mightcouldb1
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