# A host's Kokkoja

The host starts a session, invites the guests and drives the session:
puts images on the page, starts new pages, loads pages from a notebook,
and decides which guests may do the same.  In a lesson, the teacher is
the host.  Everything in [A guest's Kokkoja](guest.md) applies to the host
too; this part describes what is added, and how to install the Kokkoja
program, which a host needs.

## Installing the Kokkoja program

A guest can join from a web site with nothing installed.  A host runs the
Kokkoja program on their own computer.  It is a small Python program with
two jobs: it shows Kokkoja in your web browser, and it reads and writes
your notebooks as ordinary directories and files.  It listens only to
your own computer and talks to nothing else but the relay you name.

You need:

* **Linux or macOS.**  Windows has not been tried yet.
* **Python 3.**  Linux has it.  On macOS, open Terminal and type
  `python3 --version`; if Python is not installed, macOS offers to
  install the command line developer tools, which include it.  Any Python
  from 3.9 on will do.
* **A web browser.**  Firefox, Brave or Chrome, or Safari on a Mac;
  other browsers built on the same engines very probably work.
* **A pen tablet**, if you want to write by hand.  A mouse works for
  pointing and for rough marks.

Get Kokkoja from its repository: download

    https://git.andykopra.com/ack/kokkoja-rel/archive/main.zip

and unpack it, or, if you have git,

    git clone https://git.andykopra.com/ack/kokkoja-rel.git kokkoja

Nothing else is installed and nothing is changed on your system.  To
update later, download again or run `git pull` in that directory.
Kokkoja is free software under the GNU General Public License; the
`LICENSE.md` file in the directory is the license.  To
remove Kokkoja, delete the directory; your notebooks are elsewhere and
stay.

### On a Mac

The same steps, with four things to know:

* Terminal is in Applications ￫ Utilities.  The first `python3` or
  `git` command may make macOS offer to install the command line
  developer tools; accept, and run the command again when it has
  finished.
* The first time the program writes a notebook, macOS asks whether
  Terminal may reach your Documents folder.  Allow it, once; the
  notebooks are there.  The answer can be changed later under System
  Settings ￫ Privacy & Security ￫ Files and Folders.
* The program opens Kokkoja in your default browser, Safari included.
  To use another, start the program with `--no-browser` and open the
  address it prints in the browser you prefer.
* Wherever this documentation says Ctrl for zooming, use Command on a
  Mac.  Both work, so a hand used to Ctrl is not punished.

## Starting Kokkoja

Open a terminal in the Kokkoja directory and run

    python3 kokkoja.py --relay wss://kokkoja.andykopra.com/relay

The program prints an address beginning `http://localhost:8760/` and
opens your browser there.  Leave the terminal open: the program must run
as long as you are in a session.  Ctrl-C stops it.

The address the program prints contains a secret token.  Your browser
remembers it, so afterwards `http://localhost:8760/` alone brings Kokkoja
back; but if the browser ever says that the notebooks are locked, open
the full address the program printed.  The token is what stops any other
web page you might have open from reading your notebooks.

The relay address names the *Kokkoja server* you use.  A server does two
things: it passes the participants' messages, encrypted so that it
cannot read them, and it serves the web site that your guests join from.
The address above is Andy's server; whoever runs a server for you gives
you its address.  The program remembers it, so from the second time on

    python3 kokkoja.py

is enough, and the program says which relay it is using.  Give the
option again only to change servers.  Started for the first time with no
relay, it stops and asks for one.

Other options, all optional:

* `--notebooks DIRECTORY` keeps the notebooks somewhere other than
  `Kokkoja` in your Documents directory.
* `--port NUMBER` uses another port than 8760, if that one is taken.
* `--no-browser` does not open a browser; open the printed address
  yourself.
* `--site ADDRESS` names the web site that invitations link to.  You
  need it only if your server's web site is not at the relay's host.

## Starting a session

On the start screen, enter your name and the notebook for this session,
and press **Start a session**.  You are on page 1, a blank sheet, and
**Session** in the toolbar shows the invitation.

### The notebook

A notebook is a directory under `Kokkoja` in your Documents directory.
The start screen lists the notebooks you have; until you make one, there
is *General*, the notebook for whatever has no notebook of its own.  The
last entry of the list, **New notebook…**, asks for a name and makes a
notebook of that name, which exists from the moment a page is written
into it.  For teaching, a notebook per student works well: everything a
student is given, with everything they and you wrote on it, gathers in
that student's notebook, and the next lesson with that student starts
by choosing it again.  Your library of exercises can live in notebooks
of its own, such as *Exercises A1*, filled by keeping pages in a session
of your own with nobody else present.

The notebook can be changed during a session, in the notebook list in
the toolbar.  The page you are on then continues in the notebook chosen.

### The invitation

**Session** in the toolbar opens a window; **Invitation** there shows a
link.  **Copy** copies it; send it to
your guests by email, in a chat message, or however you reach them.  A
guest opens it, enters a name and is in.  Below the link the same
invitation stands as a QR code: a guest with a phone or a tablet points
its camera at your screen, and the link opens there.  A guest with the Kokkoja
program installed may paste it into their own program instead.  The link
carries the secret that protects the session, so send it only to those
who should be there; anyone with the link can join and read the page.
Each session you start has a new invitation.

An invitation is good as long as you keep the session open.  A guest can
join at any time, see everything written so far, and leave and return.

## Driving the session

Three buttons at the right of the toolbar are the host's.

**New** starts a new blank page for everyone.  Pages are numbered from 1
through the session.  The page being left is kept in every participant's
notebook, by itself, under a dated name; nobody has to remember to save.

**Image** puts an image file on the page for everyone.  Kokkoja's own
file chooser opens, beginning where your notebooks are and remembering
where you last chose from; a directory path can also be typed into it.
It shows small pictures of the image files it finds.  Choose one and it
is placed on the page in one way always: 5 mm below the lowest image
there, or at the top of the page if there is none, centred across the
page's width, at its natural size, in front of the images already
there.  Natural size is the size the file records: a scan arrives at
the size of the paper it came from.  A photo from a phone or camera
records no useful size and arrives at a tenth of a millimetre per
pixel.  An image wider than the page widens the page on both sides to
hold it.  From there you move and scale it by hand, as described next;
there is no other setting to choose.  PNG and JPEG files are shared as
they are unless very large; other formats, and images over 2400 pixels
on a side or 1.5 MB, are converted to JPEG and reduced first, which
does not change the size they arrive at.  A page holds up to 12 images.

To move an image, rest the pen on it, without moving, for a little over
half a second: a green outline appears, and the image follows the pen
until you lift it.  It comes to the front of the other images, which a
hold without moving also does.  To scale an image, rest the pen near one
of its corners: a green square marks the corner, and dragging it scales
the image along its diagonal, the opposite corner staying put and the
shape kept.  This works with every tool: a dot the pen may have drawn
while resting is removed, and the eraser erases nothing while it rests.
Writing is not attached to images: an image moved from under writing
leaves the writing where it was, so compose the images first and write
afterwards.  Only you and co-hosts can move images.

For a page that begins with an image, press **New** and then **Image**.
For a series of exercises, keep pressing **Image** on the same page: the
sheet grows downward and everyone scrolls through them.  A new image does
not change anyone's zoom; it appears below, to be scrolled to.

A tap of the eraser on an image removes it, whoever added it and
whenever.  Writing on it stays where it was, so remove an image before
anyone writes on it unless the writing is meant to stay.  The page keeps
the size the image gave it; **Shrink** trims it.  A guest who added an
image may remove it, even after they have stopped being a co-host.

**Fit** and **A4**, pressed by you, act on every participant's screen,
each in their own window: the way to bring everyone back to the whole
page.  A guest's Fit and A4 change only that guest's screen.

**Hide**, the tool beside the Eraser, covers part of the page for
everyone: drag open a rectangle, and whatever lies under it, writing of
anyone included, is covered in white, marked by blue corners that tell
the students something is there.  Use it to cover a solution until the
student has tried, or a part of the exercise for later.  Rest the pen on
it to move it, near a corner to resize it; a tap of the eraser removes
it and shows what was covered, and **Undo** takes back any of these as
it does your writing.  Nothing under a Hide is lost, and a
student cannot uncover it by hiding your writing on their screen: a Hide
belongs to the page, not to your writing.  A Hide is white in an
exported picture and in the page file as other programs see it.

With the Text tool, a rectangle dragged open is a *text rectangle*: a
red box with a white ground, which covers the image beneath it and no
writing, in which text wraps and which grows downward as it fills.  It
is the "write your answer here" box of a worksheet: draw it on the scan
where the answer belongs, and the student types into their own box or
beside yours.  Only its owner can type in a box, as with any text.

**Widen**, among the view buttons, makes the page wider for everyone,
until it fills your window at your present zoom: the quickest way to
more room for writing beside an exercise.  The sheet grows equally on
both sides, so nothing on the page moves.  The page keeps the new width
in everyone's notebook.  **Shrink** is its opposite: the page becomes
just large enough for everything on it, images and writing, with the
margin of 5 mm around, which trims a page down to its exercise before you keep
or export it.  A blank page cannot shrink.

**Notebook** starts a new page for everyone from a page kept in one of
your notebooks, with everything that was written on it.  A chooser shows
your notebooks on the left and small pictures of the chosen notebook's
kept pages on the right.  The loaded page is a copy: the kept page is
not changed by anything that happens next.  Each layer on it still
belongs to the participant who wrote it, so a student's answers from an
earlier lesson are still theirs, and your corrections still yours.

This is also how you return to an earlier page of the session: the page
was kept when you left it, and **Notebook** brings it back as a new page.
A lesson might go: **New**, **Image** for the exercise, work, **New**
for a point of grammar, work, **Notebook** to return to the exercise.

## Co-hosts

In the **Participants** list of the Session window, each guest's name
has a box **Co-host** beside it.  Ticking it makes that guest a
co-host: they may then start new pages, put images on the page and
arrange them, load pages from their notebook, widen, shrink and hide,
exactly as you can, and the buttons for it appear on their toolbar.
Unticking it takes it back; otherwise it lasts until the session
ends.  What stays yours alone: making co-hosts, and bringing everyone's
view to the page with Fit or A4.  Guests, co-hosts or not, can never
erase or change anyone's writing but their own; that needs no setting.

## Hiding writing

The box in front of each participant's name shows or hides that
participant's writing on your screen only.  Hide a student's answers to
see the exercise clean, hide your own corrections to see what the
student sees, show them again; the others notice nothing.  **Export**
leaves hidden writing out of the picture it makes, which is how to make a
picture of the exercise with the corrections alone.

## Keeping and exporting

The page you are on is written continuously to `Current.svg` in the
current notebook, and copied to a dated file whenever the session moves
on.  **Keep** makes such a copy now, named for the day and a serial
number, such as `2026_10_06_02.svg`; pressing it again before anything
has changed makes no second copy.  Any mark counts as a change, even a
dot from a stray touch of the pen.  Use it to mark a state worth keeping
on its own, or to add a finished page to a notebook of exercises.

**Export** saves a picture of the page as you see it, as a PNG file at
200 dots per inch, in a directory and under a name you choose in
Kokkoja's file chooser.  Replacing an existing file takes a second press
of the button, so a slip does not overwrite anything.

The notebooks are ordinary directories, and a page is an ordinary SVG
file.  Open one in a browser or in Inkscape, attach it to an email, keep
it with your other documents.  Only Kokkoja can load it as a live page
again, with each person's writing still theirs.

## Ending a session

Close the browser tab, or stop the program with Ctrl-C in its terminal.
There is nothing to save: the page is already in your notebook, and in
each guest's.  Guests who are still connected can go on writing on the
page among themselves, but no new page can be started without you or a
co-host, and a guest who arrives after everyone
has left finds an empty session.  The next lesson is a new session with a
new invitation; load the pages you need from the student's notebook.

## When something goes wrong

* **The browser says the notebooks are locked.**  Open Kokkoja from the
  full address the program printed when it started, the one with the
  token.
* **"Not connected" above the page.**  Kokkoja reconnects by itself as
  soon as the relay can be reached, and sends what was written meanwhile.
  If it does not come back, check your connection; the page is safe in
  your notebook either way.
* **A guest sees "Waiting for the host's page".**  You have not started
  a page yet, or your connection is down.  The first page is started when
  you start the session, so this usually means the latter.
* **Pressure does not work.**  The browser's console (F12) logs what
  the browser receives from your pen at your first stroke.  If it says
  *mouse*, the browser is not seeing the pen as a pen; try the other
  browser.
* **"Address already in use" when starting the program.**  A copy of
  the program is already running, usually in another terminal window.
  Only one can run at a time; use it, or stop it there with Ctrl-C and
  start again.
* **Guests cannot connect.**  Look at the line `Relay: ...` the program
  printed when it started: it names the relay the session goes through.
  If it is not your server's address, stop the program and start it
  again with `--relay` and the right address.