Voronoi on deforming object

[Cake Kid]

Hi guys,

 

I'm facing a problem in Houdini. I've been given animation of a man and I need to create skin fracture on him and blow parts of his skin away.

As it's deforming object, when I voronoi piece of his skin, voronoi pieces don't stay the same through the whole animation.

I was wondering and researching, how else could I make pieces of his skin fly away, but I am a bit stuck. I have the animation in both low res (6000 poly) and high res (100 000). We aim to render the high res model, meaning I need to fracture the high poly one somehow, without having to wait a week for simulation to finish.

Do you guys have any tips on how to tackle this problem? 

 

I'm attaching a .hip with animated sphere, showing that after I voronoi it, the voronoi freaks out on some frames.

voronoi_on_animation.hipnc

Edited December 2, 2015 by Cake Kid

[whodini]

the reason the voronoi is freaking out is because your fracture points are changing per frame. What you can do is compute the area of your geo before deformation and set your scatter node to use the area attribute this way you have points that stick to the geometry and not jitter around every frame. See this http://www.sidefx.com/docs/houdini13.0/nodes/sop/scatter#stick

[Cake Kid]

I see, thank you very much, I tried it on sphere with animated mountain sop and it worked perfectly. But the thing is, the sphere before the deformation doesn't change the position, it's x,y,z coordinates stay the same. With my animation, the whole model is moving and deforming at the same time, so when I scatter points on first still frame, they remain still until the end of animation...

I tried sticking points onto a model with uv, which works very well, scattered points stick to the geometry, but the distance of the points is changing, therefore the voronoi is calculated again causing the change of the voronoi shape.

 

I'm attaching a .hip with my basic animation and problem I explained.

voronoi animated.zip

Edited December 2, 2015 by Cake Kid

[whodini]

Heres an example, it's not perfect but it should help you get a better result.

voronoi_scatter_stick.hip

[Cake Kid]

Oh I see, voronoi chunks still change their color, when I visualise it, but they don't change the shape which is sweet! Thank you for help!

[whodini]

It's not quite perfect, if you exaggerate the anim on the box it could break the ordering of the pieces, but the shapes will stay the same on the fracture. I guess it depends on what you want to do with the fractures.

[leeseongmin]

hi

voronoi_ani.hip

[NSugleris]

Thanks for the scene Ryan, really straightforward.  

 

leeseongmin, I'm a total noob but whats the purpose of the first vopsop in the chain?

[whodini]

vopsop? I didn't add any vopsops in there. Tried to keep it as simple as possible. Or are you talking about the other hip files from the original posts?

[NSugleris]

Yea sorry I was talking about the other scene file as I'm trying to figure out what exactly hes doing in it.   

 

  Your method of using the area pumped into the scatter works great!  

[whodini]

awesome glad to help 

[Georgie]

Thanks for the scene Ryan, really straightforward.  

 

leeseongmin, I'm a total noob but whats the purpose of the first vopsop in the chain?

He's basically storing the point position from the deforming cube (twist1 node goes into input 1) in an attr called aniP and then transferring it with the second VOPSOP to the fractured geometry. 

I didn't even know that works, looks totally arcane to me but oh well, learnt something new today, can't complain. 

 

Could someone more knowledgeable please explain why that works ?

[Elizeusz]

Interesting is that You can delete those vop attr boxes and You will get exactly same effect. 

[rtep]

This is a cool hip file but I don't believe it will help you do your skin blowing away effect.  Deforming geo like this in dops usually freaks out the solver.  You'll probably have better luck using the fem solver.  You can use a facet and change your model into unique points.  That turns each poly into a cloth object.  Then in dops use a sopsolver to transfer, color let's say, to tell the cloth when to detach from the animation (using the pintoanimation attr).  Here's a bare bones setup.  Let me know if this helps.

 

simple_blowaway_cloth.hip

[rtep]

and if the bare bones setup seems like the right approach you can then use a vornoi fracture at the rest position to get a class attribute that you can use to fuse your faceted geo back together into more interesting shapes.