Issue link: https://digital.copcomm.com/i/14320
By OLIVIER MAURY “Well Bent,” pg. 26). One of the specific challenges we faced was to develop a pipeline to handle the fire-bending requirements of the show, both at the aesthetic level (our client wanted to anchor these effects in reality, while retaining some creative freedom) and at the production level (the shot count involving fire bending was fairly high). Fire has always been an important part of the visual effects landscape. On Fire F At ILM, mid-ground to foreground pyrotechnics typically would be done practically. However, it is increasingly difficult to tailor practical elements to their final-use motion and look in the shot. Tat said, filmed elements display an incredible amount of detail in a broad range of scales. Tis is one of the main reasons why it is difficult to simulate and render fire that holds up to the organic richness of practical elements. Te simulation resolutions in- volved in accurately simulating the full range of scales are usually impractical for a given produc- tion schedule. In other words, the computational power required to fit a large quantity of hero fire simulations/renders in a production schedule has not really been avail- able. One of the key factors for us is the number of iterations that an artist is able to produce and show to the client or supervisor before a shot gets finaled. Moreover, the computational fluid-dynamics models behind such simulations are complex enough that they often lead to a certain lack of control, which defeats one of our main goals of giv- ing our clients as much creative control as possible. For these reasons, digital fire has been particularly challenging and an area which we have targeted in our research and development efforts. Te advent of graph- ics processing units (GPUs) as high-performance computing devices helped us bite a sizable chunk off this hurdle. For Harry Potter and Te Half-Blood Prince, we successfully harnessed the power of the Nvidia graphics boards for high-performance comput- ing purposes. Te solver/renderer developed for that show, dubbed Verte, led to highly detailed fire renders computed in a fraction of the time Olivier Maury is a research and development engineer at Industrial Light & Magic. 10 July 2010 Simulation or the movie Te Last Airbender, Industrial Light & Magic (ILM) was challenged with bringing to life, among other things, the fire- bending effects from the animated series of the same name (see they would have taken on traditional multicore workstations. Unfortu- nately, this frustum-based solution was not appropriate for the require- ments of the Te Last Airbender’s fire-bending effects. To satisfy the filmmaker’s vision, we knew we were going to have cameras orbiting around the fire as well as fireballs coming straight at the camera, and the fire was going to have a good deal of interaction with other elemental forces, such as earth, air, and water. By August 2008, Nvidia had released Version 2.0 of CUDA, its high-performance computing development framework, which greatly For The Last Airbender, ILM had to create digital fire that met the film’s unique VFX requirements. This led to development of a new 3D fluid solver and volume renderer utilizing Nvidia’s CUDA. simplifies access to the power behind GPUs. With this framework be- coming more mature and the success of our previous experience on Harry Potter, we decided to develop a more general-purpose 3D fluid solver and volume renderer using CUDA this time; we named it Plume. From the very start, we decided to limit the use of low-level hardware optimization to a strict minimum, and built a stable and easy-to-use “grid-based computing construct” in which we could express most of the algorithms we were going to need, at the risk of not always getting optimal performance. Tis approach allowed us to focus primarily on the fluid dynamics and rendering algorithms, and we rarely had to face hardware-level issues. After six months of development, we were able to run fairly high reso- lution fire simulations: Our benchmark simulation had a grid resolu- tion of 640 x 320 x 320 and ran in 25 minutes on an Nvidia Quadro FX 5800—more than 10 times faster than for roughly an equivalent simulation to run on our multi-CPU solution. We also implemented in CUDA an artist-friendly volume renderer, including features such as self-shadowing or multiple scattering for additional smoke and render- time detail-enhancement controls. Te gain in performance allowed our artists to move from setting off overnight runs, only to have to wait until the following morning to see the result, to being able to see multiple iterations per day. Another feature we pushed forward was the integration of the simu-