Path of Exile Interviews

Official Path of Exile forums have a couple of recent in-house developer interviews. One is with the Grinding Gear Games' physics programmer, while the other one is with a game designer. Both interviews have a similar structure and touch on such topics as the interviewee's position in the company, how their average work day looks like, and what advice they can give to aspiring game developers.

Alex, the physics programmer, talks about the challenges of his particular branch of programming and dealing with unexpected bugs:

What is the most challenging aspect of programming physics for Path of Exile? Path of Exile is a very dynamic game and when implementing physics, performance is the top priority for me. Because of that, I can’t introduce any noticeable framerate drops due to physics. I was writing the Path of Exile physics engine from scratch and it had to behave somewhat naturally under completely unnatural circumstances like characters using Leap Slam with 100% increased attack speed or a Lightning Warp that basically shrinks the character to size of 0, teleports and then gradually inflates them back to normal size. A direct consequence of physics simulation for items like cloaks is them wrapping around character’s head, tangling between arms and legs and flapping all over the place when attacking 10 times a second. Introducing non-physical constraints to prevent such behaviour gets pretty tricky.


Are you able to give us an overview of what it takes to get a physics-related project completed?

When implementing game physics, you always think of the worst-case scenario. For example, what happens if the character has twice their maximum expected movement speed in a location that has twice the physics, while using various types of computer and internet connections? Making physics behave under these extreme conditions is the hardest part. The second-hardest part is integrating physics into the development pipeline of a game that has not been designed to have it.

Are there any unexpected bugs that have come up while you were working on the new cloth physics system?

We had so many experiments with all kinds of physics items. For example the very first 'physical' item that appeared in Path of Exile testing was what we call, 'Cape-Ranger' - a cape made out of the Ranger model. We had more laughs than we should have when it was flopping around characters we attached it to. I was told off multiple times for disrupting the work process by doing that.

While Nick, the game designer, discusses coming up with unique items  and the general inspirations for his design philosophies:

You were involved in the initial design of the current Breach League. Could you give us some insight into how that came about and how the idea evolved from there?

Take yourself back to August 2016. Back then, there was no such thing as an iPhone 7. We had to make do with our iPhone 6 Pluses. The current league was Prophecy, and Gene Wilder was still alive. It was a simpler time.

A show called Stranger Things had just launched on Netflix, and everyone on my Facebook feed was proclaiming it as the greatest thing ever (it wasn't -- that title goes to pizza -- but it was still excellent). Around the same time, we were trying to come up with some league concepts, and there had been a desire both internally and from our players to return to Beyond. I pitched a Beyond-themed league where the players enter the Beyond world -- a parallel universe akin to the one in Stranger Things. A place where the monsters could peer into our world, but we couldn't peer into theirs.

The idea revolved around activating a 'spire' that would send you into the parallel universe, where all the monsters in your area would still be visible, but they'd be frozen in time and untouchable, and the colours would be washed out -- an effect very similar to what we used when you first encounter the Shaper. You'd want to 'hunt' a unique monster hidden somewhere in this parallel universe, and in order to stay there longer you'd have to kill swarms of other monsters, since in Beyond the portals are powered by blood. People liked the idea, and I promptly went on vacation to Disney World, because that's just how I do.

While I was gone, it became apparent that there were a lot of technical hurdles behind the time-freeze mechanic, especially in party-play, and after implementing a few versions of the mechanic, the team landed on what eventually became Breach. They did an absolutely fantastic job making my bad Stranger Things fan-fiction into one of the most exhilarating leagues we've ever had in Path of Exile.

Part of your role involves the creation of unique items. Can you give us an overview of this process?

Sometimes unique item development is a quick, straightforward process. Abberath's Hooves is an example of a time that it wasn't. During the development of Perandus I wanted a pair of boots that shook the ground and knocked enemies back as you walked. Programmer Rian put that mechanic together quite quickly, but combining character movement with a knockback mechanic was causing a lot of bad bugs, so we shelved it.

For Breach we wanted a set of uniques unrelated to the league (but related to...something else…) that would be punchy and flavourful, and Omnitect Erik suggested some boots with a ground-stomping mechanic. So I dug out the ol' Perandus boots, removed the knockback mechanic entirely, and Programmer Mark1 suggested tying the damaging moment to the footprint event, rather than have it trigger every set duration, and programmer Alex made it happen. I loved that idea, and thought it of course also needed some footprints, so effects artist Nat made some burning hoofprints. Meanwhile 2D artist George was making the item art, and 2D artist Ash was making art for the skill icon.

Then Designer Rory balanced the skill, changed the damage type to fire to better suit the other item mods, and put it on the most appropriate base-type ever (goathide!). All of this needed to be checked by the QA team to ensure it wouldn't blow up the game. Many others checked the item in its final form, with very minor tweaks here and there. In total there were probably about 15 (maybe more!) different people who in some way contributed to the item over the course of just under a year. This is one of the more extreme collaborative examples, but it just goes to show how many people care about the details, and how much work goes into every facet of Path of Exile.