The general idea
After Rings of Power premiered on Amazon prime I had some friends approach me, mentioning it had a nice particle opening sequence that I should have a look at.
So I went to Prime and fast-forwarded trough the episodes until I found the sequence.
Although I'm a LOTR-fan, I really was just interested in this particle-animation that I've now watched like 100x. Maybe I'll give the actual series a go sometime.
I immediately liked the whole animation and thought I'd just replicate the sand-sims on one evening in Houdini for practice. But once I had started I knew I had to do some more...
Lighting and shading
Starting this project I was mostly interested in just getting the general animations as close as possible to the original. During my works however I diverged from this goal and kind of just started doing my own thing.
Although the focus still layed on the sim-part of everything I tried to give it at least an appealing look. Everything is lit by a simple spotlight-source backed up by an HDRI.
The rocks are made of glass, stone and gold materials which are randomly distributed using the particle-IDs.
Everything is rendered with Octane renderer.
A dive into POPs
Although it has mostly become my go-to software tool, I'm still very much a beginner in Houdini. This project was a great opportunity to dive into POPs (particle operators), which basically is Houdini's particle system.
I've used popgrains for most of the animations. Additionally I also tried and use RBD (rigid body dynamics) simulations for the movement of the larger pieces, but I'm yet to unexperienced with this part of Houdini and it just took to long for me to simulate it.
Although in the end I could still use RBDs to at least get an initial state for the animation of the larger rock pieces.
I've used popgrains for most of the animations. Additionally I also tried and use RBD (rigid body dynamics) simulations for the movement of the larger pieces, but I'm yet to unexperienced with this part of Houdini and it just took to long for me to simulate it.
Although in the end I could still use RBDs to at least get an initial state for the animation of the larger rock pieces.
Shapes and flow
As typical for Houdini the whole setup is fully procedural. For example I just looked up a "tree of Gondor"-SVG on the web, converted it to an Illustrator-file and took it as a base-curve for the simulation. You can see the sim-setup in the next image.
It starts with selecting the desired base-shape. Then I setup piles of grains along these lines, which will make up the main part of the sim. In addition I setup some randomly distributed grains all over the floor to make things look more interesting. These are then merged together and make up the initial sim-setup.
Next to the generation of these grain-piles I also generate flow-fields (right side/red and purple). First I take the base-curves and make them connect to each other. This makes particles "shift lanes" later, so they can transfer from one shape to another over the course of the sim. After resampling these curves are referenced by a Volume VOP. The VOP takes an enlarged version of the grain-pile's bounding box as a domain for a vector-field VDB. Using the curves the VOP can now generate a flow field that either makes particles move towards or along the curves, depending on their distance to it.
Now everything's simulated inside a popnet, using "pop advect by volumes" for general movement and "popgrains" for collisions.
Procedural rocks
In order to have actual rocks moving across the screen (and not just particle-dots) I created a selection of procedural rocks (setup below). It's basically just an Icosahedron being deformed and smoothed again. Assigning a variant-attribute to each of them I then can just randomly copy them to the simulated particles to get the final look. Since they're packed primitives everything's pretty lightweight and easy to handle in the viewport or while rendering.
Thanks for watching!
