For example, when you have such a reflective silver suit during the house fight, Doug Smythe, the digital production supervisor, helps make it easier for the TDs to create a dynamic environment map to include not only the other character but also his shadows as well. "We're still dealing with expensive ray tracing and expensive indirect," Snow adds. "We're still in RenderMan, but for some of it we used mental ray. I actually lit a shot myself during the freeway chase, and it was, to my mind, a lot more intuitive, much more like what I'd see on set using the lights. What's interesting for a lot of the artists is they're so used to using spotlights and ambient occlusion that it's conceptually weird to them initially. You're so used to the cheats. A lot of times a CG artist will turn off expediential fall off or real world-type fall off on the light so it doesn't dim out properly as you get farther away. Well, in this lighting skill, we don't have that control: if it's going to fall off, you have to boost the light's intensity, as we do on set. It does require you to think more physically correctly, but I do think that contributes to everything feeling more realistic."

Tasked with bigger and more complex action sequences, ILM used a bigger box of tools in terms of simulations, fluids and destruction.

"We leveraged improvements we've made to our internal sim engines, so we had the hydraulic fluids during the end fight and we had to add water droplets on the suits as they roll around in the water, so that's using some of the PhysBAM stuff that's getting better," Snow continues. "For the fireplace explosion, we were also able to build on some practical elements with some fluid-simulated fire where the two suits face off against one other and the RTs interact to make the effect of where the air vaporizes and create a shockwave."

The other key leverage opportunity was a greater use of Nuke and its 3D compositing capabilities, which allowed ILM to blur the line between digital mattes and compositing a lot more. This was important because there were a lot more synthetic environments and environment extension such as the climactic battle in the Japanese Garden (shot in LA) where Iron Man and War Machine face off against the drones and Whiplash.

"Out of the box, the compositor could start out with a pretty nice smoky-looking environment and mix that with volumetric-type effects for god rays coming through the smoke and rendered 3D atmospherics to create a texturally dense and interesting [look]," Snow explains. "It freed us up to make some more creatively interesting environment work."

Favreau was also encouraging about ILM's involvement in the art direction, including the arsenal of weapons for War Machine and the drones created by Bruce Holcomb, the model supervisor, and Aaron McBride, the VFX art director.