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deforming ground in impact and fracture


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Hi, I'm trying to reproduce the effect which can be seen int his video at 00:53 while using only Houdini.

The problem is I cannot figure which solver would be better to create this kind of motion in Dop (I'm a recently new user of Houdini).I've tried the Cloth solver, but there is too much deformation. I've thought of using a sop solver but I have no idea of how I could do this.Any tips to get me started?I finally found a way but I'm getting a new problem. In fact I have my ground streching on my collision plane (a default ground plane created by using the shelves).Is there anyway to make the ground staying on the collision object without loosing it's original shape?and sorry for my bad english


Edited by ioness
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I did something similar for a Nike commercial a while back:

at 00:46 when the wrecking ball impacts the wall.

You can do that with a cloth deformation, most likely that will give you 60-70% of the motion and shape that you want. So you can blend shape it with the original -- you can define a radial falloff in color and mix inside a vopsop to get closer to the precise impact shape that you want.

It's kinda like this:

*) create a medium resolution grid, perform the cloth sim on this.

*) blend your cloth sim with the original geometry based on a custom mask (1)

*) create your wall & prefracture it.

*) create centroid points for your pieces.

*) check if you can copy your pieces back onto your centroids

*) deform your centroid points with your cloth sim from (1)

*) copy your pieces onto your moving centroid points. (2) Make sure to modify your orientation based on a Normal and Up vector (or build your orient quaternion if you prefer).

-- done.... for basic setup

- for cooler results:

*) deform your pieces by the cloth sim from (1) ( this will require your pieces to have a higher level of subdivision so they can bend) (3)

*) blend your geometry of the pieces between (2) and (3) with your own custom mask. This allows you to define areas of rigidity versus areas of deformation.

*) with a sopsolver over time, you can modify your rigidity <-> deformation mask, so the material "corrects" itself from a deformed state to a rigid state.

-- this is deforming vs cracking.

Things you will need to know for this:

-- create center points for pieces -- see some of my posts on rigid body dynamics and quaternions (use search here on odforce or sidefx forums) - foreach sop

-- cloth deformation (see sidefx cloth masterclass tutorial -- some very usefull wrapper digital asset inside -- you could also use the clothcapture/cloth deform sops for this) - you should have an N and up vector attribute that gets modified as your cloth is deformed -- this is important for copying your pieces back on those center points

-- a bit of vops for blending between meshes. mix, attribute transfer for colors

-- divide sop to bricker/subdive your pieces for higher detail for deformation

-- sopsolver for attribute fading over time. (use search, plenty of examples of that).

Have fun.

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WOW Peter!

I would have never thought about using cloth sims to get a effect like this.

But I was wondering if houdini offers the same level of constrain detail as the RBD solvers in Real Flow. I went through the tutorial ioness posted a while back and I was really taken up by the idea of the new Multi Join constraints offered in Real flow 12.

They are basically the same as a glue network, with the difference that they can stretch/deform and can hold/release the new position.

That means that its more like a glue network with a wire solver applied to it.

I was wondering if you would always go with cloth simulations to deform pre fractured meshes for this kind of effect, or if it is possible to use a wire solver on a glue network to make the pieces act more like a cloth object whiles following the rules of RBD objects.

I am bringing this up, since I am seeing a small problem in your technique, and I could be 100% wrong with this, but don't the pieces that get deformed by the cloth sim intersect?

For a fast shot or a fracture in the background this won't really matter, seeing that there is going to be debri/dust covering the details, but for a close up this can prove to be a problem.

Just wondering if you ever ran into a problem with this technique and intersecting pieces, and if so how did you go about it.

My only thought is to use SDFs on all pieces and move points out those SDFs with VOPs in a for loop, but that would be deadly slow.

I am very curious on your experience with this technique and if there is a problem like intersecting pieces I would love to know if there is a better way to solve it then to use SDFs to deform the pieces so that they don't intersect anymore.



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I've some questions for the last two points in the explanation of pclaes in his post. If I understood correctly, I need to create a vector which will be considered like the direction to which the piece point and another vector which will be the UP vector, but on where object should I put these attributes? on the points to which I want to copy the piece to or on eache piece of my prefractured ground?

I don't know if I'm really clear

Edit: I was blocked for copying back the piece on the centroid but I found a way to do it and I managed to create the orient attribute but can't get the initial position of my piece back. Here is the file if somebody as the time to take a look at it.


Edited by ioness
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  • 1 year later...

Hi, after a long absence because of work to do for school, decided to finish this shot to the end, so I took back where I ended, correcting and adjusting some minor changes. But I'm still stuck when I need to create the orient attribute to put my piece back on my centroids. I tried using a polyframe from my cloth sim to create my N and up attributes, but it didn't work. Is there another way ?  since I couldn't find any orient attributes based on my sim.

Any help would be appreciated


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So, small update. Finally managed to put my pieces exactly where they needed to be. Now, I just need to find a way to make the transition beetween the static pieces and the deformed one softer. From my researches, it would be a question about the orientation of my pieces. Here is the file if you want to take a look at it and a picture showing what I want;




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