Techland's Dying Light games have stood out in a sea of zombie apocalypse titles thanks in part due to their parkour-inspired first-person traversal systems. Players aren't just rugged survivalists, they're freerunning enthusiasts who navigate an urban wasteland. There's an incredible amount of freedom in navigating these open worlds, since players can grab onto any ledge and vault over any object.

As lead gameplay programmer Bartosz Kulon and colleagues wrote in their deep dive of the first Dying Light's traversal system, that wasn't always the plan. Though simulated parkour was always in the picture, being able to go anywhere anytime was not.

But with the success of the first game's "Natural Movement system," Kulon and his colleagues had a chance to go into Dying Light 2 knowing exactly how their movement would work. So what new challenges come up when you want to do the same traversal system, but "better?"

Here's our (lightly edited) chat with Kulon about the challenges he and his colleagues ran into with Dying Light 2 Stay Human.

Game Developer: To get started, what were the biggest changes the team thought it needed to make to the Natural Movement system?

Kulon: In the first game we were experimenting a lot. This was our first take on giving the player so much freedom of movement, so we tried to do it as best as possible. I think we managed to do something really special.

For the second game we really tried to fix the things that we felt could work better, and then build the best, most natural movement system possible. We didn't have any compromises, and could use everything at our disposal. 

We hired a bunch of experts in parkour (i.e. David Belle), built an amazing mocap studio so we could record the most complex moves, and used every technology that would help us with the task. So the guiding philosophy was to not compromise on anything until we were happy with the results.

When improving the system for a new platform, you’re making a game that can handle a lot more information on the screen at once. How does this impact things like the speed of animations when the player is executing different parkour moves?

Actually, we came at it from a different angle: the first thing that we wanted is to have the best feeling and best experience for players, no compromises from technology. We built prototypes that played well and then worked to adjust it to platforms. Good gameplay results were our priority.

Were there any other challenges that came from developing this system for new consoles?

Yes. Thanks to the enhanced computation power we could handle a lot more things at once. So, we could have a more complex scene with more geometry that the player can climb on. Everything is computed on the fly, so more power was really helpful. 

Compared to the first game, the algorithms are more precise. Even if we handle more space around the player with thousands of objects, everything works fluently. This is the essence of parkour in our game.

Natural Movement scans the map and checks for areas that it thinks the player can grab onto—how does that interact with the fact that the game world changes based on player choices? How does it respond to different factions controlling (and then reshaping) different zones?

So the system is live (no offline calculations, it simulates “scanning” in real time) so it is actually very helpful. How Natural Movement reacts to the world changes in Dying Light 2 Stay Human would be…

How do things like player builds and the skill tree impact the design of Dying Light 2’s traversal? Some items and upgrades make things “easier” or at least different.

So it matters a lot. We had to constantly develop the character and the city that players play in so that they support one another. In Dying Light 1 we didn’t have side wall runs, but if you search through the internet, you will see that people managed to unlock it. We did "have it" [in the first game] but we decided to turn it off because the city was not supporting it, so it was very difficult to pull it off.

When we were designing the skill tree, we were also designing the city—each move had specific geometry that it would apply to in the city—so the player can learn what is more efficient over time.

There are no ultimate skills—the grappling hook is limited compared to the first game. But with skill and experience, players will learn that it actually can be even more powerful than it was before. I don’t want to spoil all the fun from finding it out, but I think players will like the new approach and this will make the game more addictive and fun. 

Traversing across the city can be really hypnotic and I think this is our greatest achievement that I’m really proud of.

This game uses a lot more stealth mechanics. Did adding slower segments of the game impact anything on the parkour side?

As a sandbox game, we wanted the players to be able to express themselves, so adding stealth was another piece of the puzzle. When you look at stealth games you will notice that they actually have a lot of parkour elements, like climbing, silent landings, air takedowns, etc. 

So, I think it was way easier to add stealth elements to a parkour game than the other way around. We added some features like noises on landings or fast movement, so if a player is not careful, he will make a lot of noise and stealth won’t work.

In your team’s excellent postmortem for the first game’s traversal system, you noted how implementing the Natural Movement system began to influence other departments working on the game. Did any similar shifts in direction occur with this system? Were there any lessons that helped from the first go-around?

Yes! Like I said before, we knew how important the city is and the first thing that we did was match all the sizes of it. On the city side: building height, door size, table height, street width, lamp radius, gutter size, bus stop height...millions of things. 

And then we needed to combine it with the player's abilities, like running speed, jump height, jump range, player height, crouch height, crawl height, abilities, tools…[that's] another million.

We were experimenting with everything, so it looked real and played awesome. It was a really hard job. But from those mistakes we learned a lot and managed to build something very special! I can’t wait to see players’ faces when they play the Central Loop area—I believe that it's a one-of-a-kind experience that can’t be seen anywhere apart from Dying Light 2.

I think we learned that communication is the most important thing and the more we talk with each other (i.e. Level Designers / Designers / Level Artists) the better the game will be. 

Of course COVID did not help with that, but I believe that the additional time that we took was very well spent.