Recreating Reality

Introduction

Over twelve months, I focused on replicating real-world references using Houdini to become an Effects Technical Director (FX TD). The projects below showcase my achievements in various core techniques such as rigid body dynamics (RBD), pyro, particles, vellum, and procedural modelling. Each shot has been rendered using Houdini's Karma renderer, with some utilising USD workflows. Nuke was used for compositing and the main operating system was Linux, with HQueue and Deadline for farm management.

I will share not only the final outcomes of my projects, but also the lessons learned, challenges overcome, and the passion that drives me in this field.

RBD: Recreating the Demolition of the Skyscraper Weisser Riese

On September 5th, 2021, the Weisser Riese skyscraper in Duisburg, Germany, was demolished. In this project, I've recreated the demolition utilising various core FX techniques.

Elements in the Shot

RBD-ready Buildings: The main building in the middle, consisting of four sections, was procedurally modelled without concave geometry and overlaps, featuring custom fractures for specific areas. The buildings include exterior walls, roof, roof boxes, roof rims, slabs, window frames, balcony rims and posts, as well as interior walls.

Blast Clusters: The two initial explosion clusters marking the beginning of the destruction for each middle section, generated with pyro.

The animated guides were used to art-direct the four primary RBD simulations, one for each section of the building. Additional secondary RBD simulations were used to add smaller building parts such as roof beams, balcony rims and posts, while maintaining the overall movement of the building. The ground collision was a heightfield, which also served to instantiate the trees and buildings in the environment.

The initial chunks of debris flying out from the buildings, referred to as debris bursts, were simulated using pyro. These bursts were fed as velocity inputs into the initial blast clusters that marked the beginning of the demolition. The primary RBD simulations were used as both collision objects and velocity sources for the pyro blast and burst simulations, ensuring that the building and explosions interacted seamlessly.

The RBD simulations and the velocities from the blast clusters were used to affect the vellum tarp to create the movements.

The tarp, along with simplified tree models and additional geometry, were used to collide with the pyro dust simulation. The building RBD, along with additional, hidden RBD simulations, served as collision objects and velocity interaction for the pyro dust simulation. The velocities from the blast further influenced the dust.

The RBD simulations formed the basis for sourcing the pyro dust and separating it into multiple smaller simulations.

This workflow ensured a cohesive integration of RBD, pyro, and vellum simulations.

Challenges Encountered

Working with RBD involves numerous intricate steps, including modelling, fracturing, grouping, constraint setups, simulations, and cleaning, each demanding careful decision-making and attention to detail.

Striking the right balance between accuracy in modelling and fracturing and overall efficiency was crucial, ensuring that the project remained manageable while achieving the desired level of realism.

Rendering large scenes required a strategic approach to optimise resource usage and alleviate RAM consumption. It was crucial to render early and often to identify and address potential challenges promptly. This led to converting the building to USD before rendering using a rest position and the frames stitched together for smaller file sizes.

The simulation for the dust was split into 110 separate simulations with different start frames using the same solver. Splitting simulations required adjusting the parameters differently than in a single simulation to maintain the expansiveness of the smoke. This was essential to achieve RAM usage well below the 64GB limit of the computers and, by parallelising caching, reduced simulation time from a potential 250+ hours for one computer to overnight on multiple computers.

Additional References

Group Project – Bombs Away: Recreating a Dive Bombing

For this group project we created a dive bombing scene inspired by the film Midway (2019). Through a collaborative effort and working with students from the compositing department, which provided valuable insights into a studio pipeline, we delivered a four-shot project. We established a workflow to organise and manage the sharing of the latest versions of renders, caches, assets, and more.

As the CG lead, I was responsible for several key aspects of the production, including lighting, rendering with Karma, creating tracers, muzzle flashes, oceans, and a splash.

For screenings, each effect was rendered and presented by the assigned FX TD. As the person responsible for lighting, in addition to my own effects, I was in charge of combining all the effects in the sequence, ensuring consistency and seamless integration of each aspect. This approach ensured that our final sequence was cohesive and closely matched the intense scenes depicted in the reference film.

Elements in the Shot

Workflow Overview

This workflow details the creation process for the tracers and muzzle flashes in the scene.

The airplanes were animated with sufficient pre- and post-roll to allow for proper tracking and having tracers already mid-air at the start of the shot. The guns were animated to track the specified planes, minimising additional adjustments when plane animations changed.

The tip of the barrel and the direction towards the plane were then used to generate muzzle flashes at a set frequency. A single pyro solver was employed to create realistic muzzle flashes with smoke for each gun separately.

The tracer consists of a tail and a trail. The tip of the animated gun barrel served as the emission point for a particle system, creating the points representing the head of the tracer. The trails were created by USD instancing volume variants onto these tracer head points.

Challenges Encountered

As a CG lead and lighting artist for the group project, communication was central to my role. I needed to effectively coordinate feedback and requirements among team members and integrate inputs from the instructor and compositing department.

Managing cache versions and shaders was critical to spot potential issues early and ensure consistency across the project. Keeping track of around 70 caches for simulations and animations alone required meticulous organisation and version control.

Optimising render quality at various stages and implementing efficient scene layering significantly reduced RAM consumption and shortened rendering time which resulted in splitting the longest shot into six separate layers: sky, flak, oceans and falling airplanes, background explosion, tracers, rest of the elements.

The compositing students volunteered to support us in the project of our FX TD class. However, we were one person short, so I volunteered to composite the second shot in the sequence. This gave me a more in-depth understanding of what was necessary in scene layering and AOVs for the other shots.

In my role as FX TD, deciding on the visual aesthetics for elements like tracers and muzzle flashes involved navigating diverse opinions and preferences while adhering to the project's artistic vision and reference footage. For example, tracers can range from completely straight to wiggly due to camera shake. We decided to follow the reference and implement the latter. This required tuning the wiggliness of the tracers flying through specific areas of the camera lens up or down to achieve the desired effect. The decision-making process for the muzzle flashes was similar. After screening several references for anti-aircraft guns (shown in the image under additional references), we opted to approximate the look of the muzzle flash in the primary reference and add smoke.

Learning to create realistic ocean surfaces and a water splash required rapid skill acquisition within the project timeline, as the water (flip) tutorials were scheduled for afterwards.

Additional References

Pyro: Recreating the Collapse of a Steeple Engulfed in Flames

For this project, I focused on recreating the footage depicting the collapse of a burning steeple, based on the real-life event that occurred at the First Congregational Church in Spencer, Massachusetts, on June 2nd, 2023.

Elements in the Shot

RBD-ready Steeple: The steeple was modelled by replicating the damaged state of the steeple amidst the ongoing fire.

RBD-ready Front Wall: A section of the front-facing wall was modelled using the same approach as for the steeple.

A basic animated guide was used to create an initial RBD simulation of a simplified representation of the steeple. The resulting RBD guided the simulation of the final steeple model and wall, which included interactions with the stationary church walls.

The RBD of the falling steeple was the sourcing foundation and collision for the pyro simulations of the steeple fire and the front wall fire. The collapsing steeple served as the primary source for the steeple fire simulation, while the front wall sourcing also included parts of the stationary front wall.

Challenges Encountered

The church had been burning for a while, requiring it to be modelled in a damaged state. For the steeple this meant that the thin timber-framing was exposed. This thin steeple structure collapses towards the front left, causing vertical elements to become diagonal, requiring higher resolution to be accurate. Therefore, additional steps had to be taken to remove flames from the front-facing area of the steeple and prevent stepping without overly increasing the resolution and simulation time. This was crucial for efficiency and to control RAM usage.

As the steeple fell, increased velocities acted upon it, causing the pyro simulation to generate taller flames. However, the reference footage showed the flames acting differently. This is due to the flames interacting with the complex environment, which required careful observation and adjustments to the simulation.

For the church's front wall, the horizontally spanning slates introduced moiré patterns in the renders. Addressing this required careful attention to texture detail and resolution to avoid visual artifacts.

Given the limitations on RAM and time, I focused on the core parts of the fire to ensure the project remained manageable without compromising quality.

Additional References

Vellum: Recreating Folclórico Dance

In this project, I focused on recreating the dynamic movements of a folclórico dance.

Elements in the Shot

Workflow Overview

This workflow focuses on the dress used in the scene, detailing the steps for both the shirt and the skirt components.

The shirt body is initially drawn and draped around a character in a T-pose. A vellum simulation is used to move the shirt body from the T-pose character to a shared starting stance, used by all three dancers. This shared stance is only used in the pre-roll of the shot. Using a drape, the shirt ruffle is attached to the shirt on the body. The shirt is simulated separately for each dancer with the same vellum solver.

For the skirt, the ribbons are attached to the ruffle using a vellum drape and then draped onto the skirt body. The skirt is then attached to a character in T-pose. The body is moved into the shared stance while holding onto the skirt. As with the shirt, the skirt is simulated for each dancer separately.

Challenges Encountered

It was my first time wedging caches to ensure the same setup worked for the three different dance moves. I also taught myself how to animate with Cascadeur, as animation is not part of the FX TD program.

Creating and attaching clothing pieces in Houdini required meticulous tracking of point counts to ensure all elements remain connected, allowing to increase the resolutions as the project progressed. This enabled me to have an efficient workflow. Similarly, I used a single shader despite having flags from different countries by linking a path pointing to different textures.

Making the skirt feel heavy while also catching the air was a significant challenge. Balancing these two aspects required fine-tuning the vellum solver settings and experimenting with different parameters to achieve the desired look.

Additional References

Geo: Recreating Cacti

This project focused on procedural modelling and lighting while mirroring a reference timelapse of two cacti with blossoming flowers. I recreated the details of the cacti's morphologies to capture their unique appearances and blooming patterns.

Elements in the Shot

A simple rib line is used to create a high-resolution version. Lines are instanced on it, mirrored, meshed, and modified to create a complete rib. The ribs are instanced on a circle, allowing for alternating rib placement with areoles offset and variation in the number of ribs per cactus.

The simple rib line is instantiated at the same time as the rib, forming a simple rib base. It serves as a location for instantiating the flowers, creating the spines, and forming the glochids' base.

The simple rib base narrows down the possible locations for the flowers. The flowers are instantiated together with a simplified version, while being time shifted, and bent to replicate the growth towards the sun. The simple rib base also determines the location of the new pup, with a point carried alongside the flowers to mark its position.

The glochids are placed on a surface which is created by using the simple rib base and the cactus base mesh. They are then modified by using the simple flowers in conjunction with the spines to remove intersection and position them around the flowers.

Finally, the cactus and pot are assembled to be instanced at specific locations. A generic location is used for the pup, which is afterwards moved to its final position.

For similar projects in the future, the workflow could be modified by implementing more specific operations rather than instantiations to streamline the creation process and improve efficiency.

Challenges Encountered

This project presented several challenges, particularly as it was my first project working with Houdini. I was already familiar with procedural modelling, as I have a Bachelor in mechanical engineering and had a job as Automation Specialist, creating tools to review construction drawings. It was still a significant adjustment to transition to organic shapes.

I utilised procedural techniques to model each cactus in the shape and texture of the corresponding reference cactus. Since each contained different amounts and shapes of their elements, it resulted in a complex workflow.

I challenged myself by maintaining a procedural workflow while ensuring that the glochids and spikes surrounding the flower were appropriately positioned and scaled, yet still allowing flexibility to place the flower at any other spot.

I had not yet learned vellum by the end of the assigned project time, which required a revisit of the project at a later stage to resolve the intersecting geometries.

Additional References

Summary

Each project is a journey and a new learning opportunity, not only in mastering the art of replication but in unravelling the mysteries of natural phenomena. Observing intricate mechanisms, structures, and effects allows me to dive deep into their unique occurrences and intricacies. It gives me the opportunity to research the how and why behind their behaviour and appearance, and to strive to recreate these wonders using powerful tools like Houdini. The process is not just about imitation; it’s about elevating these phenomena to new heights, making them even more cinematic and awe-inspiring.

References

RBD: Sprengung Hochhaus Weißer Riese
Pyro: Steeple Collapses at Historic Massachusetts Church
Group: Midway Aircraft Carrier Bombing
Vellum: Folklorico Dance
Geo: 4K Cactus Flowering Timelapse