bHaptics hardware on Linux

A couple weeks ago I was talking with someone on Reso about the bHaptics integration being broken for a while. There was a mod that fixed it, but was from the looks of it majorly vibecoded (with copilot as a “contributor” even), but it also worked in weird ways and introduced its own issues.

That prompted me to make my own mod that simply replaces the broken library and tries to keep everything else unchanged, the results of that you can see here.

But this also made me look into the state of bHaptics hardware on Linux, since I was somewhat interested in getting a vest, and I found out that their software is Windows-only, and it doesn’t work under Wine, bummer. I did however find a project that did the opposite, senseshift-firmware, which lets you make a device that can connect to the bHaptics player app!

The only logical thing to do next

I bought a TactSuit Air. And started writing a library to interface with it before it even arrived x3

Here I have to give a massive shoutout to btleplug, it made implementing bluetooth stuff as painless as it could possibly be, it’s a great BLE library!

Not having any real hardware to test with led me to make some mistakes along the way though, like how motors are actually indexed on the damn thing. The protocol itself is fairly simple, you either send 40 values as nibbles (that’s called a Vest frame), or a legacy frame (one byte per motor). But it seems that bHaptics did some funky on-device mapping, where a Tact Suit Air, which has 16 motors actually takes in 32 values, and motors are simply duplicated.

The battery level reading also tripped me up, because I was expecting two bytes (from reading senseshift code), but the device actually sends only one.

Other than this my code worked! So far only the Air is supported, but it should be trivial to add more devices if you own one, just take a look at models.rs:

use crate::device::mapping::{AttachmentPoint, Mapping};
use std::sync::Arc;

pub fn assign_map(model: &str) -> Vec<Arc<Mapping>> {
    match model {
        "TactSuitAirOnyx" => vec![
            Arc::new(Mapping {
                point: AttachmentPoint::TorsoFront,
                wrapping: false,
                legacy: false,
                // Doesn't actually have this many actuators, it just emulates 32...
                // should we map out the real ones instead? probably
                actuators: vec![
                    vec![Some(25), Some(24), Some(1), Some(0)],
                    vec![Some(27), Some(26), Some(3), Some(2)],
                    vec![Some(29), Some(28), Some(5), Some(4)],
                    vec![Some(31), Some(30), Some(7), Some(6)],
                ],
            }),
            Arc::new(Mapping {
                point: AttachmentPoint::TorsoBack,
                wrapping: false,
                legacy: false,
                actuators: vec![
                    vec![Some(8), Some(9), Some(16), Some(17)],
                    vec![Some(10), Some(11), Some(18), Some(19)],
                    vec![Some(12), Some(13), Some(20), Some(21)],
                    vec![Some(14), Some(15), Some(22), Some(23)],
                ],
            }),
        ],

        _ => Vec::new(),
    }
}

Making the app aandd websocket hell

I knew this would take up the most time. Games connect to the player app using a websocket, and looking at bHapticsLib allowed me to figure out the types quickly.

The first problem is that there are at least three ways to drive a device. You can use motor indices directly (dotPoint), paths on the surface of a device (pathPoints) and animations registered using .tact files (which do contain those types of points, but also a lot of other animation-related stuff). So far I only have dotPoints implemented, which means most games won’t work with my app yet.

The second problem I ran into was bHapticsLib itself, or rather its dependency WebSocketDDotNet. I’m not entirely sure why they’re using a third party library when WebSockets are part of the standard library, maybe they need to support some old dotnet version, but unfortunately this library violates the RFC. It treats HTTP headers as case-sensitive, which did not play well with tungstenite, I ended up forking tungstenite-rs and adding a patch to work around this.

The third problem is games that apparently expect the player app to be installed, and try to launch it automatically. So far that’s only Synth Riders to my knowledge, and I still need to figure out how to trick it into working.

For the GUI toolkit I went for something a bit unusual for my typical Linux dev (I usually would go for GTK4, though I haven’t written any GUI apps in a while) - egui! The reason for this is that I want it to be decently cross-platform. Even though this project is mainly aimed at Linux, I would be happy to also free some Windows users from having to use a heavy app to drive one bluetooth device.

Another thing that came back to bite me now was mapping. For dotPoints it seems like games are always expected to provide 40 points for the vest, which comes from some older vests that bHaptics used to make that had 40 motors. So far I’m not resampling this, I’m just discarding the last row, but eventually I’ll need to do that. As for other devices, as far as I know games are expected to use raw motor indices for them, which leads to interesting problems. For instance they make a device that goes on your facial interface, and it used to have more motors than the current models do, so this ended up breaking some games.

Future work

There’s a couple things I need to do to make this usable for most people. More devices, tact files, path points, better bluetooth handling (needs an option to select the adapter, because the vive pro has a built in one that likes to say hi sometimes and not work). I also would like to create an alternative protocol for games to use that is a bit saner than the bHaptics one, but from what I hear haptics like this might eventually be possible to implement using OpenXR, which would be massively preferable for any VR games out there.

For now this is enough for me to enjoy my Resonite belly rubs, and that makes me a happy creature.

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