Learning Houdini Journal 13: Windows and Shatter Nodes

Feb 07, 2016 at 12:55 am by -gToon

This is the thirteenth entry of what will be a year-long journal on learning the 3D application Houdini, created by Side Effects Software. Houdini is a sophisticated application that is widely used in the production of visual effects for Hollywood films such as Big Hero 6, Mad Max: Fury Road and many others.

In my previous Learning Houdini Journal 12, I discussed how I fine-tuned the motion and the impact of the race car in the tutorial scene I'm using to learn Houdini. In this entry, I'll go over adjusting the window the car will crash through as it flies through the air to the road below.

The aptly named "Blast node"

Getting the Window Ready
The window that the race car will crash through is well placed in the building geometry that was provided with the Introduction to Houdini 15 course from Pluralsight (formerly Digital Tutors). Following the video instructions, I selected the window parts then deleted them using the Blast node (love that name).

The next part is something I still don't quite understand. The instructor, John Moncrief, stated that it was necessary to "move the window geometry out of it's larger City Block node into its own geometry container". In order to do this, it will require creating two window geometry nodes: one with just the window and no City Block, and one with just the City Block and no window.

I understand the need to isolate the window from the building geometry in order to shatter it without affecting the larger City Block set, but I don't quite understand why two different versions have to be made.
In any event, it was simple to follow instructions and I soon had the two window nodes. This is also my first introduction to the Null node (another wonderful phrase) which is necessary in order to merge the window nodes into the building geometry.

Using the Shatter Tool

Once the actual window geometry is created (extrude node), it's a simple matter to apply the Shatter node to the geometry. Note that this new window geometry is at the Obj level along with the other major nodes like the car, the wheels and the City Block set. The default settings look good, but I'll be doing some fine tuning on the parameters of the shatter in the next journal.

At this point, I've got the car bursting out of the window, shattering the geometry and hitting the pavement below.

Shatter Node
The window after applying the Shatter Node

Fracture, Shatter and Break Things in Houdini
After I finished the tutorial, I was intrigued with the Shatter Tool, so went hunting for more information and specific tutorials on this effect. There is a lot of information out there and I'm eager to learn more. Here are some of the sites I discovered.

Sidefx has a good (if too short) introduction to RBD fracturing (what's the difference between shatter and fracture?) which is easy to follow. I also found Deep Shome's Voronoi fracture tutorial on YouTube, which is quite helpful. Finally, I ended up at Atom's Vimeo channel and found many interesting Houdini tutorials there.

Next: Fine-Tuning the Window and Working the Crash Animation