Creating a moving platform

[georgebutler]

Hi all,

We're using a custom hubs client to create a moving platform that users can get on and off. We've added a custom a-frame entity that is re-positioned every few frames to move at a constant speed, with a box mesh. We're creating this entity on the client and using NAF client commands to start and stop the platform. What are your opinions on this approach, is there a more ideal way to go about doing this?

On top of this, we've considered using the nav entity from Spoke to create a "moving NPC". Maybe this would be an alternate solution?

@robinkwilson If you have any suggestions or input that would be fantastic.

[netpro2k]

The trickiest part here is going to be that moment in hubs is not based on the physics system but a navmesh using https://github.com/donmccurdy/three-pathfinding under the hood. You are going to need to figure out a way to either dynamically update the navmesh as the platform moves, or take into account some sort of offset of the platform when doing navmesh lookups.

The other tricky part will be keeping things in sync over the network. Just syncing the start/stop like you are doing might be "good enough" but there is latency so every client is going to have a slightly different opinion about where the platform is, so you will likely get some visual artifacts. (This is quite common in many multiplayer games with moving platforms, and is the sort of default state of things unless you specifically try and account for it).

One way I had considered implementing this sort of thing in the future would be to us an "occupable" waypoint that moved. Right now waypoints only update the players position when you first occupy them, but it would be fairly trivial to have them do it every frame, so that the player would essentially be "snapped into" the waypoint as it moved around. You would not be able to walk around on the "platform" which is a bit restrictive, but would avoid having to do anything fancy with the navmesh. You could imagine writing code to have you automatically enter/exit the waypoint as you reached the ends of the platforms path.

[mkremins]

Thanks for the reply! This seems in line with what we were expecting / have seen so far. For context, being able to walk around on the platform (and see others walking around on the platform) is important to us, but it's pretty slow-moving and not "drivable" – think a large flat "barge" that moves along a pre-planned path more than, e.g., a car.

Do you think it'd be feasible or desirable to suspend gravity on the avatars "inside" the vehicle and control their y-position manually via our own code, instead of relying on the navmesh to dictate walkability?

[netpro2k]

There is no "gravity" on the avatars, their movement is entirely driven in the character controller by the navmesh. You could certainly override this behavior while they are considered on a moving platform. This is how "fly mode" works, and how waypoints can move the character around and disable movement.

https://github.com/mozilla/hubs/blob/master/src/systems/character-controller-system.js