The idea behind these videos was to challenge myself and put together something different both in presentation style and content. Houdini is excellent for this kind of work, and I mostly appreciate seeing it used for special projects or simulations that do not fall into the usual everyday FX spectrum. I believe that's where the true power of the software lies, in its flexibility and adaptation with any kind of VFX project.
In the "Pyro | POP" Paint example I used 10 different Particle Sims to control the overall "star" shape. It can easily be done by just one simulation but I wanted to have some more manual control over the initial look and density. So the first "POP - SIM 01" is actually 10 small simulations merged together. Everything else on the project is sourced from these initial Particles, including the main and 10 secondary Pyro Sims. They were then colored during render time, with a custom shader that transfers Cd values from Particles to the Pyro Sims using some Point Cloud nodes.
All final Renders are created from the same simulations; changing only colors, particle positions and scene lighting.
1. For anyone who wants to create something similar I would suggest focusing on the Particle Simulation. Getting this part right is crucial to achieving the same result. Put as much detail as possible in this stage because as you will notice during the compositing breakdown, Pyro Sims are actually complementary to the final look.
2. Some variation in shape and size is very important when rendering particles. In this instance, a small part of them was rendered as geometry, using a Copy SOP and some procedurally created geo that resembles the big chunks of powder paint. The rest of the Particles was rendered as points, using a Point node and a fit() expression on the pscale parameter.
3. During compositing I used the Pyro Renders as Matte Layers for the Particles. In this way I could get the Pyro to look as positioned between the Particles without needing to render any extra passes.
The RBD workflow starts with the model preparation. I used a scan model for this demo. Converting it to VDB and using the VDB Combine node helped me create the hollow shape of the statue. After converting the geo back to polygons it's usually a good idea to retopologize your model. Keeping the poly count as low as possible can help you speed up your simulations and fracturing process.
1. During the RBD Sim play around with GravityForce values, not only to control the mass and scale aspect, but also time. Some really small Force values like -0.02 (or even lower depending on your scene) can give your simulation a slow motion look.
2. When creating your Fluid Sources for the Pyro Sim, use Motion Blur in the Scalar Volumes tab in order to avoid chunky results (often present when your broken pieces are moving too fast). My default settings range from 6 to 8 Geometry Samples and a small Blur Offset from -0.1 to -0.2.
In the future I hope to have again the opportunity to share some more similar projects and maybe even more tips and tutorials.