Lesson Learned: No sticky slime or tar in VR games

I have this interesting VR specific game design problem I ran into and wanted to share.

In my game, I have this sticky type of grease which can be sprayed onto the ground. Any creature moving through it has their movement speed reduced by 50%, presumably including the player.

Here’s where it gets tricky: How does this work with room scale VR? Let’s say that normally I can move forward in the game at 1 meter per second by physically moving 1 meter in 1 second. I have a 1:1 match between physical movement and game movement. However, if I walk through the slime, now my movement ratio is 1:0.5. This is unexpected and breaks immersion because you suddenly are confronted with this disconnect between your own physical movement speed and the game movement speed. We know how far we’re moving in physical space because we’ve got a lifetime of experience moving around, so when our visual indicators don’t match our physical indicators, we are like, “whoa, what’s going on here? I don’t feel so good…”

So, this brings us to a new rule in VR: don’t design elements into the game which would cause the player movement ratio to stray from 1:1 in room scale VR.

An interesting experiment would be to look at where the threshold for movement ratio begins to get uncomfortable. How does 1:0.95 feel? What about 1:1.05? If we have 1:X, where X is a number between 0->5, what values of X cause the most disconnect? It would be cool to eventually get a graph of these values found through empirical testing. I suspect that the values of 0.0 and 1.0 have the most comfort.

What about visually impairing the player, like blurring the screen or fading to black the faster they move while on slime to kind of force them to move at a certain speed? I can see how it might not be ideal but it might also work alright.

Well, what’s interesting is that if the player moves in their physical space, you don’t want to restrict their movement speed. However, if they’re using your artificial locomotion solution, it’s fine because they don’t have their own body giving them physical / spatial feedback. So, if you put in something into your game which changes the movement speed of a character, it’s probably not a good idea, but maybe it’s okay to let the player “cheat” by letting them move at full speed by physically walking? Maybe playing audio cues would be sufficient for communicating that they’re walking in tar / slime, and you can slow down the animation speed and footstep play rate and give the illusion that they’re moving slower, when really they’re not. Maybe they won’t notice? I’ll have to experiment.