haptics!

https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/radial-controller-protocol-implementation

With a little bit of trial and error (and a crash-course in how the heck
HID even works), I figured out how to get the dial to provide haptic
feedback!

Along the way, I also learned that you can take advantage of the
(incorrectly named) Resolution Multiplier field to customize how many
"steps" the dial should have, offloading the work to the device itself!

Very cool!!

README.md

@@ -4,6 +4,7 @@ A Linux userspace controller for the [Microsoft Surface Dial](https://www.micros
 
 - Uses the [`evdev`](https://en.wikipedia.org/wiki/Evdev) API + `libevdev` to read events from the surface dial.
 - Uses `libevdev` to fake input via `/dev/uinput` (for keypresses / media controls)
+- Uses `hidapi` to configure dial sensitivity + haptics
 
 **DISCLAIMER: This is WIP software!**
 
@@ -34,33 +35,42 @@ It would be cool to create some sort of GUI overlay (similar to the Windows one)
     - [x] Scrolling / Zooming
     - [ ] \(meta\) Specify modes via config file(s)
 - [ ] Dynamically switch between operating modes
-    - _currently required re-compiling the daemon_
-    - [ ] Context-sensitive (based on currently open application)
-    - [ ] Using `surface-dial-cli` application
+    - _currently requires re-compiling the daemon_
     - [ ] Using some-sort of on-device mechanism (e.g: long-press)
-- [ ] Haptic Feedback
-    - This is tough one, as it doesn't seem like the kernel driver exposes any haptic feedback interface...
+    - [ ] Using `surface-dial-cli` application
+    - [ ] Context-sensitive (based on currently open application)
+- [x] Haptic Feedback
+    - https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/radial-controller-protocol-implementation
+    - https://www.usb.org/sites/default/files/hutrr63b_-_haptics_page_redline_0.pdf
+    - https://www.usb.org/sites/default/files/hut1_21.pdf
+    - _This was tricky to figure out, but in the end, it was surprisingly straightforward! Big thanks to [Geo](https://www.linkedin.com/in/geo-palakunnel-57718245/) for pointing me in the right direction!_
 - [x] Desktop Notifications
     - [x] On Launch
     - [x] When switching between sub-modes (e.g: scroll/zoom)
 
 Feel free to contribute new features!
 
-## Building
+## Dependencies
 
 Building `surface-dial-daemon` requires the following:
 
+- Linux Kernel 4.19 or higher
 - A fairly recent version of the Rust compiler
 - `libevdev`
+- `hidapi`
 
-If `libevdev` is not installed, the `evdev_rs` Rust library will try to build it from source, which may require other bits of build tooling. As such, it's recommended to install `libevdev` if it's available through your distribution.
+You can install Rust through [`rustup`](https://rustup.rs/).
+
+Unless you're a cool hackerman, the easiest way to get `libevdev` and `hidapi` is via your distro's package manager.
 
 ```bash
 # e.g: on ubuntu
-sudo apt install libevdev-dev
+sudo apt install libevdev-dev libhidapi-dev
 ```
 
-Otherwise, `surface-dial-daemon` uses the bog-standard `cargo build` flow.
+## Building
+
+`surface-dial-daemon` uses the bog-standard `cargo build` flow.
 
 ```bash
 cargo build -p surface-dial-daemon --release