How Horizon Forbidden West, Sea of Thieves set the bar for video game water

How the studios behind ‘Horizon Forbidden West’ and ‘Sea of Thieves’ created their games’ spellbinding seas

Water graphics in “Sea of Thieves” (Video: Xbox Game Studios)


The first time I saw the waves in “Horizon Forbidden West,” the 2022 open world adventure set in post-apocalyptic California, they took my breath away. In the first Horizon entry, “Zero Dawn,” water was comparatively flat and motionless, sitting next to land rather than interacting with it. But in “Forbidden West,” the waves rise, swell, break and crash in striking 3D, as if in concert with the sand below. If you choose to direct the game’s protagonist Aloy into the undulating water, she will bob up and down, the sunlight reflecting brightly off the water, her movements casting the gentlest of ripples.

Water graphics in “Horizon Forbidden West” (Video: Sony Interactive Entertainment)

Water is the latest element of the natural world that AAA game studios have looked to render with eye-popping fidelity. Great strides in the density and detail of vegetation have been made over the past ten years. Lighting in many newer games just looks real, glinting off and diffusing through various materials. And yet, as Jan-Bart van Beek, art director for “Forbidden West,” explained over a video call, water and other substances like gas and snow that appear chaotic and complex in their form and movement “are hard problems to solve in computer effects.”

Effect is the key word here: What many games — including “Forbidden West” — actually do when it comes to water is create a visual illusion, rather than a computationally expensive fluid simulation that behaves like water. The outcome looks great and appears to move with liquid-like realism, but it won’t melt your home console or PC the way a full simulation might.

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Convincing computer-generated water has long been a fixture of movies, thanks in no small part to the aqua-obsessed oeuvre of Hollywood director James Cameron. But getting video game water right requires more work than just porting over the techniques of cinematic VFX. Movies have the luxury of being able to task supercomputers with rendering a single frame of CGI footage for hours, van Beek explained. But games, by virtue of their interactivity, have “about five thousandths of a second” to display whatever virtual phenomena the player is looking at. When you factor in the increasing demand for 60 frames per second as opposed to 30 (essentially halving the time for such calculations to be made) that makes creating these water simulations even more technically challenging.

But for van Beek’s team, which works at the cutting edge of interactive photorealistic graphics, that challenge is precisely why they got into the industry.

“This is nerdy, hardcore graphics engineering,” van Beek said. “It’s the stuff we love to do.”

Set on the California coastline — famous for surfing — it was imperative that “Horizon Forbidden West” nail the look of the ocean’s crest and resulting foam.

“In the ocean, you might say that the water moves up and down,” van Beek said. “But every part of the surface actually moves in circles. It moves up and then it moves a little to the side and then moves out again. That’s basically why you get those choppy wave forms.”

Real-time editing of water graphics in “Horizon Forbidden West” (Video: Sony Interactive Entertainment)

The game is able to render this type of swirling movement easily enough (which looks suitably realistic once you add a variety of graphical effects). But showing the wave break is much more complicated, van Beek stressed.

“The water doesn’t just go up,” he said. “It actually falls over and then crashes onto itself. It almost becomes a completely different shape.”

To create this effect, van Beek and his developers first rendered a computationally expensive wave simulation of the kind seen in high-end moviemaking like “Avatar,” exporting that 3D model, and creating a series of 2D images that show the wave’s shape.

“It’s prerendering the effect to a certain extent, but then storing it in a way that can be used in real time,” van Beek said. In a follow-up email, he clarified: “These are not images like a normal photo. The pixels don’t describe colors, [they] describe a shape.”

Real-time editing of water graphics in “Horizon Forbidden West” (Video: Sony Interactive Entertainment)

That series of 2D images was then, in essence, layered atop the 3D wave. As the wave gets closer to the shore, changing shape, the 2D image changes with it, appearing to show the wave cresting, and subsequently, breaking. Crucially, “Horizon Forbidden West” barely breaks a sweat while doing so, maintaining its high frame rate throughout.

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It’s a huge amount of effort, not least because water — specifically that sloshing about near “Horizon Forbidden West’s” shore — isn’t even crucial to the gameplay. For van Beek, the ever-moving ocean feeds into what he described as one of the game’s key pillars: the “exploration of majestic nature.” This is everywhere in the game, from foliage, to rock formations, to the restless wind.

“That’s what our waves and water really lean into,” he said. “[To make] exploration really interesting, rewarding and magical.”

The ocean water’s bulges and contractions exert a greater influence on play in the online pirate adventure “Sea of Thieves.” Its deep water simulation conjures up the uneasy terror you’d find watching videos of ships battling the nautical elements. Your boat careens from side to side and up and down, ocean spray dissipating over the deck as you maneuver across the high seas in search of treasure — or enemy vessels.

Mark Lucas, lead rendering engineer on “Sea of Thieves,” explained that the starting point for the game’s water was a 2001 paper by Jerry Tessendorf, the VFX guru behind the water in “Titanic.” Because Lucas and his colleagues knew that they wanted to replicate the vertiginous swells of the deep ocean, they needed “large, high amplitude, low frequency waves” — or, simply, epic but infrequent motions. For the ripples on the surface, it was the inverse: high frequency, low amplitude waves. They took the math that would create all of these overlapping waveforms and used another mathematical tool called the Fourier Transform to convert them “into the actual physical shape of the water surface,” Lucas said.

The secret sauce, the reason the ocean in “Sea of Thieves” looks so “lifelike,” Lucas said, is the pairing of this already complicated math with the Phillips spectrum, a model created in 1958 by noted geophysicist Owen Martin Phillips. According to Lucas, this model explains how “ocean water behaves based on meteorological analysis.”

The game’s water, Lucas points out, is only possible because of a large, decades-old body of research. “It’s a lot of people working in lots of different fields that have all contributed to it,” he said.

Water graphics in “Sea of Thieves” (Video: Xbox Game Studios)

Lucas thinks that the water in “Sea of Thieves” now nearly meets the standard of the world’s most celebrated movie effects.

“We’re actually doing the calculations almost at the quality level that was used in ‘Titanic,’ but in real time,” he said. “We’re one notch down.” The reason is twofold according to Lucas: the miracle of modern graphics processing units and nearly an ocean’s worth of code optimization.

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Graphical innovations and efforts at realism might feel standard in blockbuster video games these days. But when it comes to video game water, each swell and break is an opportunity to see the twin foundations of video games — art and technology — working in unison. Alongside recent advances in the depiction of natural phenomena like snow and wind, the rendering of water represents a further heightening of visual ambition. Partly, this stems from a desire to push forward the technology for future games.

“You develop these things for a game and maybe you’re already imagining how it could develop further,” van Beek said. Often, though, such efforts serve the pursuit of a single magical moment.

“A lot of people ask, does the audience really care? And we think so. We care,” van Beek said. “When you’re playing a video game, maybe you have one of those moments where you go, ‘Oh my god, that almost looks real.’ It’s always an amazing feeling for us, as well as for gamers. For a moment, even briefly, they can get lost in the world and feel that it’s completely believable.”

Lewis Gordon is a video game and culture writer. His work has appeared in outlets such as VICE, The Verge, The Nation and The A.V. Club. Follow him on Twitter @lewis_gordon.

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