VANCOUVER - During the "Capturing the Infinite Universe in 'Lucy' - Fractal Rendering in Film Production' session at SIGGRAPH, Alex Kim and Daniel P. Ferreira from Industrial Light & Magic talked about their fractal rendering techniques used to bring the surreal, hallucinatory cloud-like particle elements to the screen for the film Lucy.
The production design used elements of nebulous vapory forms based on the images of fractal math pattern which have literally infinite complexity. The basic problem the team faced was how to represent this potentially-limitless challenge in ways that could be effectively laid out, collided with and interactively lit. They did this through a hybrid approach that took advantage of different tools and approaches exploiting their respective strengths while avoiding the weaknesses.
They first looked at available fractal rendering tools, but these were all scientific tools aimed at the accurate mathematical representation of the data. Of course these did not provide the level of control and art directability that a feature film demands. They also wanted to avoid the expense of developing yet another expensive in-house rendering solution where existing readily-available tools could provide them with what they needed.
For the coarse representation of the data, they relied on low-resolution approximations of the mathematical data using the open source OpenVDB volume data format developed at DreamWorks. These could be turned into low-res stand-ins suitable for layout and scene choreography. They could also derive suitably-scaled models for collisions, secondary dynamics and lighting effects
But the real challenge was how to capture the seemingly-limitless complexity. To get the beauty renders they leveraged a screen space adaptive distance technique in Houdini. The first place to dice up this problem is to solve only what you see. They did this by projecting particles from the plane of the camera directly onto the mathematical equations thereby limiting the complexity to exactly the image pixels needed. Shadowing was handled by applying the same technique from the light sources - "looking through" the lights as if they were cameras and checking for where these "light particles" occluded the "camera particles."
For a greater degree of volumetric complexity, another particle pass was used and rendered in Krakatoa - a dedicated high-performance particle renderer - to render billions of extra particles streaming from the original screen space hero particles. By rendering the accumulation of so many points, the desired vaporous, ethereal, cloud like effects were achieved.
It was definitely an example of necessity being the mother of invention, or in this case, time and resource constraints being the mother of inspired innovation.
Scott Singer is a Digital Effects Supervisor at Tippett Studio. He can be reached by email at: ssinger@tippett.com.