https://github.com/funkey/recept

Pen event interception for line smoothing on the reMarkable 2 tablet
https://github.com/funkey/recept

Last synced: about 2 months ago
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Pen event interception for line smoothing on the reMarkable 2 tablet

• Host: GitHub
• URL: https://github.com/funkey/recept
• Owner: funkey
• License: mit
• Created: 2020-11-08T05:19:05.000Z (almost 4 years ago)
• Default Branch: main
• Last Pushed: 2023-05-04T20:25:49.000Z (over 1 year ago)
• Last Synced: 2024-05-18T19:37:02.307Z (4 months ago)
• Language: C++
• Size: 1.91 MB
• Stars: 162
• Watchers: 20
• Forks: 13
• Open Issues: 13
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-reMarkable - ReCept - Fix for the rM2 jagged line issue. (Device Tools / Launchers)

README

        
ReCept: Remarkable Intercept

============================

A small library to intercept and smooth pen events on the [reMarkable

2](https://remarkable.com/) tablet. This fixes the infamous "jagged lines"

issue some users of the reMarkable 2 experience.

![before vs after](images/before_after.png)

Disclaimer

----------

This is not an official reMarkable product, and I am in no way affiliated with

reMarkable. I release this library in the hope that it is helpful to others. I

can make no guarantee that it works as intended. There might be bugs leading to

device crashes.

Installation

------------

You need access to a Linux machine to install the fix. On that machine:

1. Connect your reMarkable 2 with the USB-C cable.

2. Clone this repository, i.e., run `git clone https://github.com/funkey/recept` in a terminal.

3. Change into the repository with `cd recept`.

4. Run `./install.sh`.

The install script will make several `ssh` connections to your device. For

that, it needs to know the IP address or hostname of your device. If you

haven't set up public key authentication before, it will also ask for a

password. You can find both the IP address and password in "Settings" -> "Help"

-> "Copyrights and licenses", at the bottom.

If you want to uninstall the fix, simply enter `0` when asked for the smoothing

value in the install script.

Will it increase the latency?

-----------------------------

In short, yes. The pen events themselves are not delayed (the filter itself

consists only of a handful of integer operations, which are likely negligible).

However, since we forward the average position of the past `N` events instead

of the actual event, the reported position is somewhere close to the `N/2`-last

event received. How much that actually increases latency depends on how fast

events come in. As an example, if the pen sends 1000 events per second and the

filter size `N` is 8, the mean will trail the actual pen position by around 4

milliseconds. This calculation assumes isochronous events, which might not be

the case.

How does it work?

-----------------

`ReCept` uses the `LD_PRELOAD` trick, which in this case intercepts calls to

`open` and `read`. Whenever `/dev/input/event1` is opened by `xochitl` (the GUI

running on the tablet), `librecept` remembers the file handle. Subsequent

`read`s from this handle are transparently filtered with a moving average of

size 16 by default.