Simulating Destruction in Houdini
Hi, my name is Hadrien Palanca, I am a freelance motion designer and FX artist based in France. I do 3D works for commercials, TV, live events, music videos, and all kind of stuff.
For me it all started back in 2000-ish, I loved playing video games but I get bored with every game I play real quick. So I started to play with Cinema 4D. For me, it was like another video game where I could play with balls hitting bricks and physics engine.
When I was in college I studied a lot of things (economics, law, history) but not in art. I learned everything by myself (well, with the help of great online teachers also). At that time, I was also involved in a student association (I had a ton of parties!) and we felt the need for some teasers and animated 3D logo in order to sell more tickets for our parties. So I started to learn everything I could in a more professional way within After Effect and Cinema 4D. I immediately enjoyed it and decided to make a living of it.
I have always been passionate about destroying things, so I kept an eye on Houdini but never dared to take the leap until I saw the VFX breakdown of the movie Attraction from Main Road Post. That was it! Too much for me! I decided to take a leap and learn Houdini whatever it’d cost. And it cost me A LOT of time! But in this journey, CGMA helped me a lot.
CGMA Courses for Houdini
I am kind of extreme when doing things. I bought a lot of Houdini courses available on the internet (Rebelway, Applied Houdini, Renascence Program, Pluralsight, and more) and studied them as much as I could (at a given point I was studying Houdini 14 hour a day). I was willing to know everything I could.
At CGMA, I took the 2 Houdini courses for destruction – one with Keith Kamholz, Mastering Destruction in Houdini, and the other with Manuel Tausch, Intro to FX Using Houdini. I am really happy to have taken them in this order because I was still kind of new to Houdini when I took the first one, and Manuel’s course is really tough!
I think by looking at both of my results you can see the progression, especially in the smoke simulation. Those two courses really helped me to learn a lot within Houdini.
Impressive Destructions in Houdini
You want to have a clear idea of what your destruction will look like because you will fracture your geometry according to that. There’s no point to fracture a part of a building that is not supposed to break, right? For this, your geo must be as clean as possible (no intersecting geo or unfolding geo). After that, you fracture it and get it ready for simulation.
Then, you stack multiple sims on top of each other.
The point is not really to build a “physically correct” destruction. Houdini constraints are not aware of weight, for example, a thin paper-like piece of concrete could literally handle the weight of a whole building. The point is rather to build destruction which looks plausible to you and is as pleasing to the eye as possible.
There are multiple technologies allowing to build destructible structures and simulate fracturing. Here, I used the bullet physics engine. It has been designed for games initially and is now widely used in VFX for handling large numbers of rigid body pieces. You work with physics by giving attributes to pieces that the solver will then understand: speedmax, spinmax, gravity, all sort of information that you give to the solver to have the desired look. There are no good or bad settings I believe, there is only what’s working for your project or not working.
If you are interested in the current state of the technology behind destruction, here is a pretty good article exposing the technology that is being used and that will be used in the future.
The dust effect is not that complicated, it is a combination of 3 simulations: particles sim for the dust with grains, smoke sim, and a rigid body sim for rocks.
A growing circle around the character (in the Tower Destruction) scatters points on it and according to the center emits more or less smoke/density. Everything is driven by this smoke sim.
Usually, you want to iterate quite a lot and tweak settings, so it’s necessary to start with fewer pieces, lower collision resolution, fewer sub-steps like that in order to have quick feedback and test which values work best. And then, when you are happy with the behavior of your pieces, you crank everything up.
Advice for a beginner: I would say that no shot will ever be perfect so the most important thing is to try and get better every time. Obviously, if you are a beginner it will not be impressive at first but try, fail, repeat… until your result gets really good.
For me, the most challenging part of Manuel’s course was to combine my daily freelance work with weekly assignments that you have to do. That’s really a lot of work which is not always easy to manage with high demanding projects.
As for the shot itself, I would say that it was the clustered fire sim that I did for torches inside the tower. I had to do multiple clusters for every torch so it was challenging to understand how things work and make the solver understand how to resize dynamically the simulated area for each torch. I ended up with a real mess in my network and some torches actually aren’t very well simulated but, overall, you don’t really notice that.
Recommendations for Learners
When it comes to giving advice to the beginners, it’s really personal but I would recommend not to start 3D with Houdini. Perhaps, it’d be better to start first with something easier to have a solid foundation of the principles in 3D and then move on to Houdini.
I started with Cinema 4D and if I had to understand both how 3D works (textures, UV, normals…) and how Houdini itself works I don’t know if I could have made it.
If you already know 3D, then start with a general introduction which explains what every button does and how Houdini works. That’s not as exciting as a fancy tutorial on building destruction, but you if you have a more solid understanding of Houdini you will be able to use it in every situation. That is not always the case for a tutorial on a specific effect. Once you get a good grasp on Houdini, I would then recommend Applied Houdini from Steven Knipping. For me, this is the where you can get the most valuable information out of your money and believe me, I have bought A LOT of Houdini courses!
CGMA courses were both (Manuel’s and Keith’s) really helpful and full of great production-proven techniques. This was gold! Especially for me because I don’t work in a studio environment full of Houdini killer artists ready to share tips and tricks with you.
I have learned so much within those two courses that it is hard to point out a particular thing I have learned. But I would definitely recommend both courses at CGMA!