Week 07+08: RBD Destruction Simulation
Project Mid-Checkpoint
I. The Art of Refinement: Weeks of Iteration in Houdini Destruction
Destruction work in Houdini is rarely a one-and-done process—it's a meticulous cycle of refining, reworking, and troubleshooting, where every small tweak can mean the difference between a chaotic mess and a beautifully orchestrated collapse. Over the past few weeks, I’ve been deep in this iterative grind, pushing each element of my RBD setup toward greater efficiency, control, and realism.
One of the foundational changes was reworking the tiled ground, which was initially offset from the center. This misalignment made it difficult to properly reference impact points and establish meaningful connections between fractured pieces. By recentering the ground, not only did I streamline the workflow, but I also set the stage for a much cleaner and more efficient simulation down the line.
Active Attribute Improvements
It was important to standardize the @active attribute into a strict binary 0 or 1 system, ensuring fractured pieces remain fully static until they are explicitly activated, stabilizing the destruction sequence completely, preventing unwanted motion and preserving the integrity of the destruction sequence. Here is a point-based visualization of the active attribute at its final activation masking frame.
2. Velocity Attribute Continuation
Perhaps the most challenging part this week was troubleshooting velocity transfer. The issue stemmed from an incorrect transfer level—while packed primitives exist at the point level, each represented by a singular primitive centroid, the velocity was mistakenly applied at the primitive level. This caused the fragments to show no velocity response at all. Once the transfer was correctly switched to the point level, the velocity propagated as expected, allowing the destruction to react dynamically and with proper energy distribution.
All these refinements weren’t just technical fixes—they were essential steps toward creating destruction that feels grounded, dynamic, and, above all, believable. And as always, with Houdini, the journey of refinement never truly ends, and I believe there is always room for improvement in any project. including this one. Once I found success in transferring this attribute, I was able to make any final shaping changes, ready to start the simulation process.
II. Structuring the DOP Network: Laying the Groundwork for Fracture Simulation
The DOP Network for the fractured RBD system is structured with a clear, efficient hierarchy to ensure accurate motion and energy transfer. At the core of the setup is the RBD Packed Object, which represents the fractured ground surface—each fragment neatly packed and carrying the velocity (v) attribute for precise motion control.
One key aspect of this setup is the procedural connection between the ground plane and the modeled tiled ground. By dynamically linking the two, the ground plane is accurately placed on the grid, ensuring proper alignment and seamless interaction with the fractured geometry. This eliminates any manual positioning errors and keeps the system adaptable to changes in the environment.
Week 06 Shot Comp and Breakdown
The first pass of the simulation is now complete, with key forces in place—including gravity—allowing the fractured pieces to settle naturally. This milestone sets the foundation for further refinements, such as secondary fracturing, debris, and fine-tuned velocity shaping to achieve a more realistic destruction sequence.
Week 06 Shot Comp with Reference Video Shot
Week 06 - Shot Comp with Reference Backplate
Week 06 Shot Comp Without Reference Backplate
a. Procedural Debris Modeling & Fracturing
To ensure variety and realism in the debris, five unique debris pieces were procedurally modeled and fractured using the Boolean Fracture technique. This approach allows for precise control over breakage patterns while maintaining natural irregularity in the shapes. The Boolean method enables us to create convincing chipping, splintering, and jagged edges that react properly in simulations.
These pieces serve as reusable debris elements that can be scattered dynamically, ensuring that the destruction feels varied rather than repetitive. Their procedural nature allows for easy adjustments to size, fracture density, and edge detailing as needed.
1. RBD Debris Setup
III. RBD Debris & Particle Setup: Enhancing Destruction Realism Through Layers
b. Sourcing Debris from the Fracture
Debris should originate from realistic points of impact. The best source for this is the inner faces of fractured geometry, which become exposed as pieces break apart. By scattering points on these surfaces, we ensure debris appears only where it makes sense.
A further refinement is checking for neighboring fractured pieces—this helps identify areas of intense breakage where more debris should be concentrated.
D. Scatter Density & Activation Timing
Once the pre-activation process is complete, we control how much debris is generated and when it activates.
Scatter Density is carefully managed to avoid excessive or unrealistic debris. Denser scatter is used in high-impact areas, while lower densities prevent unnecessary clutter.
Activation Timing ensures debris appears only when the fracture occurs. Each point is assigned an activation frame, allowing it to spawn at the right moment rather than all at once.
With the neighbor-checking attribute wrangle already processed, activation timing is now influenced by proximity to the primary impact. This staggered approach prevents unnatural uniform spawning and enhances realism.
c. Pre-Activation Calculations and Processing
Before activating the debris, Attribute Wrangles are used to analyze the fracture network and determine activation behavior. The main purpose of this step is to check neighboring fractured pieces and their distances to understand the spread of destruction.
Using functions like nearpoints() in VEX, we can evaluate which debris elements are closest to major fractures and assign them priority for activation. This ensures that pieces near the impact zone activate first, while those further away may have delayed activation or spawn in secondary breakages.
This pre-processing step refines the natural progression of destruction, ensuring that debris doesn’t activate randomly but follows a logical sequence dictated by fracture connectivity and spatial relationships.
2. RBD Fine Particles Setup—Similar sourcing and Activation Techniques from Debris Setup Applied
The sourcing for dust particles follows the same logic as debris, using scattered points on exposed fracture surfaces. However, instead of directly instancing geometry, the dust particles are instanced using a POP Network (POPNet). This approach makes the workflow more efficient by allowing procedural particle control, including lifespan, velocity variations, and turbulence, without manually placing instances.
To enhance realism, the activation of dust is offset by 3 frames, creating a staggered start as the breakage and explosive destruction take their course. This slight delay ensures the dust blooms naturally after the initial impact, following the momentum of the fracturing debris.
By layering both chunk-based debris and fine particles, the destruction feels grounded and physically accurate.
A convincing simulation isn’t just about fractured pieces—debris and dust play a crucial role in selling the scale, energy, and impact of destruction. To achieve this, we focus on four key aspects: debris modeling, sourcing, scatter density, and activation timing. This method aligns with techniques shared by industry professionals like Gabriel Neville, an FX Lead at MPC FILM, ensuring a production-ready approach that adds realism to destruction effects.
Flipbooks of the RBD Major Fragments, Debris, and Particles Simulations
Concluding Thoughts and Observations
Through procedural modeling, precise sourcing, pre-activation processing, controlled scatter density, and staggered activation, debris and dust seamlessly integrate into the RBD simulation. Following industry-standard techniques, this extra layer of detail makes destruction more believable, ensuring that every fracture not only looks dynamic but also behaves in a way that enhances realism.
Observations & Refinements Post-Simulation
After running the simulation, several key observations were made regarding the behavior of the active attribute and velocity-driven fracture dynamics:
The active attribute triggers the fractured pieces in a ripple effect, starting with a lower velocity activation before a secondary impact-based explosive reaction takes over. This second phase carries much higher velocity and propagates through the fracture region as the ripples expand.
One potential enhancement to explore is implementing RBD cluster groups to create a more dynamic and complex fracture activation pattern. This could improve the peeling-off effect of pieces as velocity progresses outward from the centroid to the edges of the mapped fracture region.
Other technical aspects that require refinement:
Weight & Resistance Forces: The inherited velocity of triggered pieces currently lacks the correct weight feel. They follow their velocity trajectory too strictly, missing natural air resistance and secondary resistance forces that would affect their movement. Additionally, the angular velocity needs refinement, as pieces don’t spin or tumble as expected.
Camera Setup & Composition: One of the major pieces of feedback was that the camera framing does not match the shot camera. The current scene feels too close, whereas the reference shot has a more distant, high-angle view. Studying the lens type, focal length, and aperture settings of the reference camera could help make necessary adjustments to better match the cinematic composition.
Debris & Particle Optimization: Additionally, the debris and particle setup can be further optimized, as simulating particles proved to be more challenging than expected due to performance inefficiencies. Improvements in instancing, caching, and simulation resolution could help streamline the process and reduce computational overhead while maintaining visual quality.
These refinements will further enhance the realism of the destruction sequence, making the shot not only visually compelling but also physically accurate.
REFERENCES
Rebelway Ground Impact Debris Tutorial for certain aspects of the RBD Debris and RBD Particles setup.