Solar Ash is the second game from Heart Machine, the independent developer team that turned out Hyper Light Drifter. Though both titles are science fiction/fantasy adventures set in brightly-colored worlds, they're drastically different in how they let players move and fight through their worlds.

In Hyper Light Drifter, the titular Drifter character is controlled in a top-down camera view. Combat is designed around paying attention to enemy movements in a system with a high skill floor and equally high skill ceiling. Enemies have recognizable attack patterns, but those patterns move quick and hit hard.

You would think a studio that mastered this kind of combat system would want its next game to build on such a system (especially while From Software continues to pump more life into similar systems in games like Elden Ring and the Dark Souls 3), but that's not what happened. Solar Ash is a 3D game more invested in player traversal than tight combat. But that's okay, because it uses its smooth traversal system as combat.

Solar Ash's player character, "Rei," glides across alien landscapes, relying on a simple attack and grappling hook to strike down smaller enemies. These are just stepping stones on the way to fighting Remnants--huge creatures standing in the way of the Rei being able to save her homeworld.

What led Heart Machine to design a brand-new combat system? How does going from 2D to 3D spaces create different kinds of difficulty? Alx Preston, co-founder of Heart Machine, and creative director on both titles, talked to Game Developer about how the studio evolved its thinking on combat design, and explained how the team came to take a different point of view on difficulty. 

Learning a new instrument

"If we were playing the trumpet with Drifter, then we learned how to play the violin with Solar Ash," Alx Preston said with a laugh. He explained that at the heart of the combat switch between Heart Machine's two games was the jump in camera perspective. Three-dimensional space operates very differently from two-dimensional space. A third-person camera performs differently from a first-person camera. 

And with the team's initial interest in making a game that focused more on traversal, that complicated things by "several orders of magnitude," Preston said. 

As noted above, traversal and combat are inextricably linked in Solar Ash. All combat in Hyper Light Drifter took place on flat, two-dimensional arenas, while Solar Ash's combat involves hills, grinding rails, skyscrapers, platforms, and more. 

To make combat work in this space, and to keep movement fluid, Preston said that Heart Machine had to have the player character not stop moving while she's attacking. This allows smaller enemies to actually fold into the level design. They can't be core parts of platforming sections (since defeating them would mean players couldn't proceed if they fall to the ground in a later section), but they can shape player behavior.

One section in the game's second area feels like a great example of what Heart Machine was trying to pull off. While trying to reach an objective that will send a Remnant into the open world, players navigate through an array of eerie ruins. In one of these ruins, a wall-mounted enemy launches high-speed projectiles at the player. 

Dodging these projectiles requires that players keep moving, and its presence on the wall lets players execute a grapple attack that closes the gap and pulls the player close to their goal. Some enemies in these positions can be used as stepping stones to access less accessible areas.

It's a field of merged design (combat and traversal) that Preston actually says the the team wishes they'd been able to do more of. "It was fun to do the stuff we did, but we only just scratched the surface," he confessed. "You always have some grand ambitions, that there are things that just don't make it at different times."

Or in other words, you can learn to play a violin, but when you perform your first recital, you'll know that there's so many ways to play you haven't learned yet.

Bringing down big beasts

After players glide through ruins, spar with small monsters, and complete short timed platforming puzzles, the real action begins. Remnants blocking the players' ultimate goal come to life and start wandering through the open-world areas. Players can start their attacks on the Remnants anywhere in their loops. But attacking Remnants doesn't rely on mashing the "attack" button, it's an exercise in completing three straightforward loops across the beasts in order to grapple onto different weak points.

Preston said these Remnants were at the heart of Solar Ash from its original pitch all the way to ship. They aren't just "levels" set up in the center of the area however. "They have a lot of the same components that the static levels do, except we spent a lot of time trying to figure out how to motivate them, and get them to ambulate," he explained. 

Some of them float, some are bipeds, some...do other things. Designing a "boss" here means having level designers designing levels and traversal. Engineers need to design inverse kinematics to motivate limb movement. And of course they all need to feel unique, not just look unique. "You need to devise systems that are unique to keep players engaged on the backs of these things," said Preston. 

And the biggest challenge in their creation, Preston says, was merging their level geometry with the art direction. He described it as a "constant battle" to ensure they looked impressive and full of life, and not just blocks hanging out in the sky. 

A big technical accomplishment with these creatures is their ability to navigate existing zones that don't feel inherently shaped for their presence. Players start each run on the boss by using the grapple attack, so it was fairly easy to make sure those were located on the beast's bottoms, and players couldn't exploit bosses just by leaping from a higher building.

But an actual challenge was ensuring that the Remnants who used legs to walk around could actually do so in a way that felt natural. As Preston put it, "A biped walking around doesn't have to just fit the space, the space has to fit them."

Designing these creatures--and their movement--was obviously a huge resource timesink. But Preston says a big reason the creatures resonated with playtesters had a lot to do with camera placement. The camera "matters a whole lot," he told us. When it's zoomed out, it can show not only the creatures, but the player character in context to the creature, which can really sell the sense of scale.

Zooming too far in while the player is fighting on a creature's back made it feel like a standalone level that didn't need to be in the open-world space. 

Some key moments of scale delivery needed to be done through cutscenes, others happen when the player strikes the creature and it cries out in terrible pain. 

If any of this is starting to sound like Shadow of the Colossus--yeah, those beautiful monsters were definitely an inspiration for Preston and his colleagues. But Preston said the higher emphasis on speed and gliding traversal meant Heart Machine's monsters needed narrower paths than Team ICO's creatures. 

"They're intended to be more linear experiences. They're intended to be high speed and high stakes," he noted. "With that tension, with that speed, you need to focus down and narrow your scope so that players can really dig into the thing that matters the most like executing [a perfect attack] on a constrained timeframe."

These big beasts are the culmination of players' time investigating Solar Ash's different open-area zones, and when you square off with one you can feel all the careful craft and consideration that Heart Machine put into their creation. It's always a little sad to watch them fall to the ground.

Thinking about the player

Moving from 2D to 3D for Heart Machine sounds something like how game developers made the same jump between the SNES/Sega Genesis Era to the PlayStation/N64 era. "Constraints really matter for this stuff," Preston said, thinking back on Solar Ash's 4-5 year development cycle. He described how earlier iterations of the game allowed much more open movement in more spacious terrain. 

"We're asking a lot of the player," he said. "In a 2D environment, you've got the full playing field, generally speaking, and it's much easier to understand the context of what's happening around you and strategize." 

"But in 3D--especially with a free form camera--you are asking the player to do a lot. And that's something that we came back to over and over again."

Heart Machine watched as, to their befuddlement, players just didn't look up that often. Some really didn't interact with the right stick of a gamepad. And though Solar Ash wasn't only meant for experienced players, experienced players were among those who just seemed to forget what they could do while playing the game. 

Part of why this happened had to do with Rei, the Voidwalker character. In other games with 3D combat, the knowledge that you're a humanoid creature attacking and defending is easy to grok. But Rei is an alien adventurer, gliding on clouds like they're an ice rink. It made combat much more open and much more fluid. Previously solved problems in 3D combat aren't solved any more, and Heart Machine hand to wrangle with new design problems.

These challenges did hit some of Heart Machine's scope ambitions for Solar Ash, but Preston seems comfortable with where the game landed. He said that by picking and choosing what the "essential pieces" of the game were, it--and the player's experience--turned out all the better for it.