![]() At the time I thought it was because I had implemented the thing wrong, but in fact it was just that the Successive Over-Relaxation and forward-integrated timestep techniques described in the paper were fundamentally unstable. The final shot features one or two of these instabilities, which I was unable to get rid of. ![]() The simulation pretty much worked, though it encountered instabilities in most of the simulation attempts – areas where pressure would suddenly increase and cause a ‘pop’, creating a big splash which filled back in with water. It’s amazing to me that we got anything done. The old ILM “DOALL” scripts had three phases – RENDER, COMP, and ABBY, the last of which sent the shot to the Abekas. Even playback was a big deal back then – our machines couldn’t play back image sequences at speed, so we had to go to a special room with Abekas disk drives to view our results. Though the simulation was self-contained, it output particles in the Wavefront PDB file format, so that they could be read and played back by Dynamation, which was how we reviewed results. By that time I think I had some initial tests to show. Ben Snow was my CG Supervisor and as the 5 week mark closed in he gently let me know that I had to get something working. But I look back on those weeks with such fondness – I worked around the clock, and was fairly stressed out. I only had C at the time, not even C++, and I was not as experienced a programmer as I am now. This paper helped provide a framework and an anchor for my vague and ill-formed particles-in-cubes idea, and I set about attempting to implement it as quickly as possible. Nick Foster was at the time working at PDI Dreamworks on creating water simulation for the movie Antz. A few times during those early years at ILM I snuck into the library at Berkeley to copy papers, so that must have been how I found this paper back then. I can’t remember how I found the paper, as this was long before we used the internet to readily find resources like this. All of the paint fixes in the shot were done by the amazing Patrick Jarvis, working in Matador and painting with a mouse.Ībout two weeks into the shot, with six weeks to go, I encountered the 1996 Foster-Metaxas paper on fluid simulation, which described a Particle-In-Cell voxel grid solution of the Navier Stokes equations for incompressible free-surface flows. Fortunately the shot was amenable to these constraints, though in the final render of the simulation there were clear places where the water was separated from the building edges and had to be paint-fixed. My cube array was very coarse – 64圆4x32 – and furthermore I could only accommodate collision objects (buildings) that were aligned wholly with the cube walls and were perfectly aligned to the grid. My idea was that if a cube filled up with more particles than it could hold, it would disperse some particles to neighbouring cubes, and this would have the global effect of creating a fluid-like flow. I was foolishly optimistic and energetic, and came up with an idea after talking with my office neighbour Jeremy Goldman, which involved creating a voxel grid (I didn’t know it was called that at the time, so I called them a stacked cube array), in which particles would be binned.Ībove: watch a clip of the whole sequence. The overhead shot (which was called wc9) had been worked on by several other TDs who were exploring ways of achieving the look via texture deformation in shaders, but without much success. When I joined, there were only 8 weeks remaining until the project wrapped. Vfxblog: What are your memories of the requirements of that aerial NYC tidal wave shot, and what steps you took to achieve it?Ĭhristopher Horvath: I joined Deep Impact after being on Snake Eyes, which was my first show at ILM. Digital effects artist Christopher Horvath, only very new to ILM at the time and later the co-founder of Tweak Software, was behind the CG simulations of that overhead shot.įor the film’s 20th anniversary, Horvath spoke to vfxblog about ‘jerry-rigging’ the solution for that shot, and his memories of working on Deep Impact, and later founding Tweak. One shot I specifically remembered from the film was an aerial view above some New York City skyscrapers of the water smashing in between the gaps in the buildings. This was still early days in CG water, and ILM used several techniques to achieve different kinds of water shots. The film had a wide array of visual effects work from Industrial Light & Magic – from spacecraft miniatures to digital comets and, perhaps most memorably, a swathe of wave and water simulations. Mimi Leder’s Deep Impact is now 20 years old. “I was foolishly optimistic and energetic.” – Christopher Horvath Remembering this killer ILM shot from Deep Impact
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