Back in May, the gameplay clip that had everyone talking was of a lava bridge in The Legend of Zelda: Tears of the Kingdom. Developers were impressed by the game’s robust physics engine, noting that getting something like this to work in a game is an incredibly difficult task.
But why is that?
I interviewed two game developers about working with gameplay physics, and what Tears of the Kingdom does that makes it stand out from other games.
If you play games you probably have an idea of what I mean when I say “physics” but it’s worth going over the fundamentals because, like most aspects of game development, the more you think about physics the more complicated it gets and the more miraculous it seems.
In games, anything that moves is basically either a canned animation, or a physics object.
“[Physics] covers things like collision, movement, acceleration, even character controls,” software engineer Cole Wardell told me. “A lot of it is trying to solve these very complex equations in a way that is both fast and does not cause a lot of error.”
Game physics are tough because there’s a lot of math going on to make us believe that a digital rock is falling to the digital ground in a way that doesn’t break our immersion.
As an immersive sim, Tears of the Kingdom’s physics are trickier than most. The interactions that the player can cause are incredibly complex. Wardell points to a door that is pulled open by chains attached to rotating tires.
In most games, something like this pulley system would be a canned animation, or the points where the chain attaches and their effect on the door would be faked in some way.
“But later on in that, in that dungeon,” Wardell said, “you’re given just wheels, and the chains are hanging there, and you have to build it yourself.” After expermenting with the door, he was able to find other ways to lift it by attaching the hanging chains to different points.
“That bridge and the chain are really the same thing,” Wardell said. “Because if you think about it, all of them are a bunch of segments connected by hinges. That’s how ropes are done in a game engine.”
A functional video game rope or chain isn’t a continuous object — it’s basically tons of segments, and when one of them moves, the others react. That can easily create a, ha, chain reaction where the whole thing freaks out because every segment is reacting to every other segment’s movement ad infinitum. That’s why most games don’t prioritize rope collision.
Tears of the Kingdom doesn’t fully prioritize rope collision either. The chains on your horse cart clip freely through objects. And the chains that lift this stone door aren’t available in other parts of the world, certainly not as portable Zonai devices. They’re too complex to use outside of this curated scenario.
“It felt like the programmers had extra time, and were just flexing on the people that knew what was going on,” Wardell said. “It almost felt like a little nod from the developers to people who work on engines going, ‘Yeah, yeah, this thing is pretty cool. We can do some great stuff. It’s that stable.’”
That stability is part of why the bridge over the lava was impressive, too. I asked game producer Shayna Moon what they noticed in the clip. Previously Moon worked on God of War and God of War: Ragnarok.
“The most critical thing is that it all is working,” Moon said.
The bridge is composed of interacting physics objects, intersecting with the lava, and being tugged around by the player.
“There are so many different things interacting,” Moon added. “Like, all of that stuff is really impressive. And it’s the polish and the stability, like the lack of bugs, that really makes it stand out.”
If it were easy, everyone would do it. But also, everyone doesn’t need to.
As special as these physics interactions are, they work for Tears of the Kingdom because the game is largely about manipulating physics objects and creating marvelous contraptions. The physics need to sing. That’s not true of every game.
“Game developers make choices every day of development,” Moon said. “And most of those choices revolve around, ‘How do we get to the experience we want the player to have?’”
Not every game needs to have an incredibly complex physics engine. But according to Moon, part of the reason Tears of the Kingdom stands out is that it feels like the developers had time to accomplish what they wanted.
The game’s producer Eiji Aonuma said in an interview with The Washington Post that Tears of the Kingdom was functionally done in March of 2022, but the team was able to delay it an entire year to keep working on it. Shayna said they would be surprised if that year wasn’t devoted to optimizing these physics interactions that make up so much of the game.
“We are really kneecapping ourselves by our overreliance on contract labor,” Moon said. “I personally, at a time, was working on a game that was expected to have about a two-to-three-year development cycle. And I was able to hire but I was hiring contractors.”
Moon was able to hire contractors for a period of 18 months. Then the contractors would be let go, and Moon would hire more contractors to finish out the development cycle.
“I said to my manager, ‘So, we’re going to lose these people right as we’re starting to finalize this game, and I’m going to have to bring on new people and teach them how all of this works,’” Moon said. “And my manager basically said, ‘Yep, that is what we’re gonna have to deal with.’ […] The way that we work, the way that we burn people out, is really undercutting our future, because the games industry is only going to get bigger.”
So when it comes to Tears of the Kingdom, the real miracle might just be that the team had time to figure all this out. Nintendo made a game with a physics system so robust that you can make Beyblades and EVAs and Mad Max cars and almost anything you can imagine.
Check out the video above for an extended discussion of the topic, and make sure you subscribe to Polygon on YouTube for more.
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