rm2canvas

A html canvas based screencasting server for the reMarkable 1/2 digital paper systems. It draws live on the canvas from the remarkables touchscreen input, but also fetches ground truth via occasional screenshots from the remarkable, trying to (seamlessly) integrate these two.

Why is it cool?

  • High quality screencast, with native 1872x1404 resolution (These are unfortunately a few seconds old, bad for live presentations)!
  • Instantanious updates on what is drawn/removed on the rm via the Wacom pen (30 times per second)!
  • Smooth interpolation between those two!
  • Low data usage: Updates are only send if there is something to update. As the event stream is rather small and the PNG backgrounds are just updated every few seconds, the whole streaming experience uses just ~20-50kb/s.

These features make it ideal for streaming a course too many students. That's why I developed it, at least.

Usage

  1. enable SSH access on your remarkable
  2. If using a rm1: TODO (should be quite risk free, just read /dev/fb0?)
    1. If using a rm2: Place the screenshotter GO programm (see https://gist.github.com/owulveryck/4007cbf14e0028f373e4294f66c4ad07) in /home/root/screenshot.arm on your device. A binary compiled by me lies in the repo (screenshot.arm)

Warning: Please be aware of the risks of running go code as root on a potentially brickable device. Be especially aware on software updates of xochitl. I do not think that there are extended risks, but please try to understand what this script is doing.

  1. Install imagemagick as we both need the convert and the compare tool as well as websockets via pip.
  2. start the server via python3 server.py HOSTADDRESS, where HOSTADDRESS could be either localhost or some IPv4/IPv6 address. This opens a (maybe publicly reachable!) HTTP Server on Port 7622. Be aware that the file request sanitzier was programmed at 02:53 in the morning.

ToDo:

  • enable rm1 support. Should be almost trivial, I just don't have any device to test this with.
  • remove canvas strokes with a smooth transition instead of abruptly deleting them (eyecandy)
  • Hunt bugs. Please report any you encounter!
  • Fix rotation.

Planned bigger features

  • detect swipes to new pages and save a backlog of pages in the html
  • Make setup easier
  • Switch to a "real" http server, not something made in websockets.
  • Make HTTPS support easier

GitHub

https://github.com/flomlo/rm2canvas