Half-Life: Alyx's movement system was changed because tall testers kept getting stuck

Half-Life: Alyx features a trio of locomotion options, letting you move through the environment normally, blink teleport, or shift teleport. The two teleportation styles are functionally the same, but one takes you to your destination almost immediately, while the other jumps there. Those movement systems are the subject of a new deep dive video from Valve. 

Valve's developers show off a bunch of prototypes and some of the problems they had to solve that are unique to VR games. Player height, for instance. Valve decided it wanted to reflect the height of a player in the game itself. There's a practical implication to this, as it affects hows paths are computed. 

"Early on, we would get hard-to-reproduce bugs from players banging their virtual heads on low-hanging pipes because they were unable to teleport through certain areas," says Valve's Greg Coomer. "It was only later that we realised all those bugs were coming from our taller colleagues."

In this version of Alyx, players had to duck before they teleported if there was any obstacle in their path, but Valve found that players often didn't notice the obstacles because they were too focused on their goal. The solution was to create a standard minimum body size when teleporting, effectively making every player the same height while they're moving from A to B. 

Players focusing on their destination above all else was something Valve apparently noticed throughout testing, as well as players having very high expectations about the extent of their abilities. 

"Playtesters would happily tell us that yes, in fact they could reach that spot by squeezing through a gap, catapulting over an object or sliding under an obstacle," says Coomer. 

Testers would peer under gaps and around corners and try to find novel ways to get through the maps, so Valve had to make sure that the end position of the players body was a valid one and that there was a clear path for them to reach it. You can't slide through a metal grate or through a tiny crack in the wall, but you can contort your body to get through narrow spaces that a person would conceivably be able to slip through. 

Elsewhere, the video explores how Valve used audio to support movement, why it created partial movement and a whole host of other things the studio learned and experimented with throughout Alyx's development.  

As Emma wrote, Half-Life: Alyx is full of clever tricks to reduce motion sickness, something that puts me off the vast majority of VR games. But if you're still not sure VR is for you and still want to try Alyx, unofficial non-VR versions are in the works.