Shang-Chi: Bus Battle
Karen Moltenbrey
November 12, 2021

Shang-Chi: Bus Battle

In the film Shang-Chi, we are introduced to the characters via flashbacks. After the flashbacks, we are transported to modern-day San Francisco, where we find a grown-up Shang-Chi and his friend Katy catching a bus to work, but en route are ambushed on board by the Ten Rings gang as they try to steal Shang-Chi’s pendant. The driving force behind this sequence: Luma, which crafted approximately 150 VFX shots for this high-energy fight on what became an out-of-control runaway bus rambling through San Francisco.
According to Alex Cancado, Luma’s VFX supervisor, a large portion of the sequence was filmed against bluescreen in Australia using two articulated bus rigs — one 40 feet high and placed on a gimbal for the extreme motion (shaking, flipping), and the other used for general driving. Another rig, with a 360 Arri camera array, drove through pre-determined streets in San Francisco, and that 360 video was then stitched together and used as a background for many of the shots behind the actors. “So, the majority of the shots when we’re inside the bus looking outside, it’s basically a combination of the bluescreen rig with the outside scenery from the 360 shoot in San Francisco,” Cancado explains. “That was the simple part of the project.”

The more complex part involved shots from outside the out-of-control bus as it is moving more erratically and destructively. “For those shots, we still used parts of the rig and the shots inside the bus. But then we stitched and added those into a combination of a 2D bus with a full CG bus that we had built for moments that were full CG,” Cancado says.

Moreover, Luma constructed a CG build of the necessary city sections based on location plates, Lidar scans, projection mapping, and photography reference, with extensive previs and stuntvis done by The Third Floor. “The combination of using plate projections for the buildings so we didn’t have to build every single one in 3D was successful. It adds realism and keeps things grounded without us having to create everything from scratch,” says Cancado. The artists also built a number of full-CG elements (all the props, trees, the streets themselves, the windows for the right reflectivity, the inside and outside of the bus). At times, the group used projections with photos, while other times the work involved an all-CG environment.

“We had a perfect representation of how every one of those streets looked in 3D. Then, using the Lidar, we built and retopologized on top of it all the geometry we needed for the buildings. And then we put the camera in a spot where the photo [of the area] was shot, and we would project that back into the geometry,” explains Cancado. “Almost like you’re spray painting in every one of the buildings, but they already have lighting and texture, so it already looks like a city. But then we had to light the props and street to match those.”

To build the environment, the group used a combination of Maya and Pixologic’s ZBrush for modeling and Foundry’s Katana for rendering, along with other tools. Compositing was done in Nuke, while sims and other work was accomplished in Houdini.

As Cancado notes, the biggest technical challenge for this lengthy sequence was building the CG environments with the outside of the bus, which is also CG, then adding the plate to those and making sure all the angles worked. “Imagine they were shooting those elements inside a bluescreen but trying to pretend you’re visualizing how a bus is driving, and making it look real and making sure people don’t know what’s CG and what’s not — that was pretty challenging,” he says.

In addition, Luma created digi-doubles for inside the bus that reacted appropriately to the mayhem. A digi-double was also used in the final fight on the bus between Shang-Chi and Ten Ring’s Razor Fist, so named due to the CG blade the artists crafted that projects from his arm.