As of Monday, “The Eight Hundred” became the highest-grossing movie of 2020 at the global box office, overtaking “Bad Boys for Life.” To date, the Chinese war epic has raked in $425 million and continues to exceed all expectations.

The film is based on a true story, depicting a Chinese battalion who mounted a determined defense of the Sihang Warehouse from the invasion of the Japanese army in 1937 Shanghai.

From combat scenes to aerial attacks, Rising Sun Pictures worked on the principal effects for the war epic that spans four days — with much of the action taking place on the third day centering on the relentless aerial attack.

Visual effects supervisor Tim Crosbie (“X-Men: Days of Future Past”) breaks down two key sequences from the film including why he needed to build a green screen for some of the rooftop sequences.

The Airstrike Sequence

We started working on that back in December 2016. We did the blocking and choreography. By Jan. 2017, we started working with the DP, Yu Cao. We did snippets of previz to see if what we had decided in the storyboard would work. And one thing the DP said, was “It’s too Hollywood.” So, we dialed back on some things and bought other things back in again.

We knew we would be shooting on the roof, and in the concessions ( also known as The Bund, where the fighting is witnessed by thousands of foreigners and Chinese civilians) to look up to the roof for some of those wide shots. Thankfully, drone technology was up to the level where we could use those instead of helicopters. But the only constraint was that drones can only go at a certain speed.

One of the things we found out as we were getting close to shooting time was that the roof itself, although it’s built and reinforced, and it was supposed to have people shooting on it — in the original planning, they weren’t entirely sure whether we’d be able to get an entire camera kit up there. We were thinking that we might need to have hefty cranes and might have to get off the roof – this was six stories up.

But there were safety issues, and we ended up having to build a replica of the roof and wrapping it in green screen so we could jump between the two. The warehouse set was more than a kilometer in length and over two kilometers of green screen, 15 meters high.

With regards to difficulty level, it was is probably more of a headache for people actually trying to schedule which roof we were going to be on and which day.

We had CG set-extensions, showing the ruined city of Shanghai to augment production footage of the practical warehouse set and we used the CG set-extensions to show the thousands of individual buildings and other structures, many in ruins, as well as debris, fire, smoke, snow and other atmospheric elements.

For the sequences where we knew we were going to be blowing things up, and we knew we needed smoke running, I had long chats with Yu Cao because we needed smoke on set since it affects how the lighting changes – it diffuses a lot of the lighting around on the characters. At the same time, if we had a lot of smoke on the real roof, trying to match it on the bottom roof with the green screen around was going to prove difficult and cause some very interesting continuity issues. Much of it was practical. But just to give you an idea, we put down something like 28 kilometers of high tension cables buried under the ground.

The End Sequence with the Soldiers running across the bridge.

The set was practical. From the North Bank to the South Bank was about half a mile long. It was about half a mile wide for the river. When we arrived, it was all marshland and it took us two years to build that riverbank.

Concerning how the lighting was set, Yu worked with his gaffers and grips. This goes back to the days when you didn’t have VFX, you had to build practical. We still had to do a. lot of VFX. We built out to the horizon for 1937 Shanghai. We couldn’t do a little bit of CG and some 2 ½ D projected painting because there were huge long aerial shots. Some of the camera shots traveled a mile and we had no other choice, but to build it practically.

We added snow to probably about half the shots. But most of the time, it was more enhancing what was there.

The rigs that were built were the size of a reasonably sized house. On a still night, the snow dropped straight down, you could have a large rig, sort of near to the camera. Even though you may not get snow in the deep background, it still feels like you’ve got pretty good coverage. Our job in those scenarios would have been to put the snow in the background, especially where all the lit areas are. However, when you get a bit of wind, you suddenly get these pockets where there was no snow, so we had to seamlessly put in CG snow when you couldn’t get practical.