# LuaML: An experimental markup language and 'browser' for it

Demo of a simple structured editor for formatted text atop an infinite 2D
surface that can be panned and zoomed.

For ease of implementation, LuaML documents are always legal Lua objects
rather than a first-class language like HTML. A simple example:

```
{ type='text', data={'hello, world!',} }
```

Text object data consists of an array of strings, one for each line. No
newlines at the moment. (Everything is subject to change.)

You can draw various shapes on the surface:
```
{type='line', data={0,0, 0,600}},
{type='line', data={0,0, 800,0}},
{type='text', data={'0'}, x=-20,y=-20},
{type='rectangle', x=50,y=50, w=20,h=80, r=1,g=0,b=0},
{type='text', data={'abc', 'def'}, x=150, y=50, w=50,h=50, fg={r=0,g=0.4, b=0.9}},
{type='circle', x=300,y=200, radius=40, r=1,g=0,b=1},
{type='arc', x=0,y=0, radius=50, angle1=0, angle2=math.pi*2/3},
{type='ellipse', x=100,y=100, radiusx=10, radiusy=50},
{type='bezier', data={25,25, 25,125, 75,25, 125,25}},
```

But most of the design effort so far has focused on the 3 text types:
* `text` for runs of text to be line-wrapped over the given `width`.
* `rows` and `cols`, the only hierarchical types, ways to compose `text` nodes
  into various grid layouts.

Some more examples.

Adjust foreground/background color (akin to a `div` with inline `style`):
```
{ type='text', fg={r=1,g=0,b=0}, bg={r=1,g=1,b=0},
  data={'hello, world!'}
}
```

Two-column text:
```
{ type='cols', data={
  {type='text', data={'first column'}},
  {type='text', data={'second column'}},
}}
```

A table with two rows and two columns:
```
{ type='cols', data={
  { type='rows', data={
    {type='text', data={'abc'}},
    {type='text', data={'def'}},
  }},
  { type='rows', data={
    {type='text', data={'ghi'}},
    {type='text', data={'jkl'}},
  }},
}}
```

(With the current design, cols of rows seem strictly superior to rows of cols.
Column boundaries line up consistently across rows.)

This is still quite incomplete. Come help figure out its future. Currently
supported "attributes":
  * `fg`, `bg` for color (no `blink` tag yet)
  * `margin` (used as `margin-left` or `margin-top` depending on whether the
    parent node has `cols` or `rows` respectively)
  * `width` in pixels (I'd like to add '%' units here.)

Since this is all Lua, unrecognized attributes are silently ignored. In the
app itself you'll see attributes like `name` and `doc`. (This is a nightmare
if you imagine this turning into some sort of long-lived standard with
versions and compatibility guarantees. I don't. I just want an app-internal
format for creating UIs with very little code.)

LuaML.love is a fork of [lines.love](http://akkartik.name/lines.html), an
editor for plain text where you can also seamlessly insert line drawings.
Designed above all to be easy to modify and give you early warning if your
modifications break something.

## Getting started

Install [LÖVE](https://love2d.org). It's just a 5MB download, open-source and
extremely well-behaved. I'll assume below that you can invoke it using the
`love` command, but that might vary depending on your OS.

Run this app from the terminal, [passing its directory to LÖVE](https://love2d.org/wiki/Getting_Started#Running_Games)

You'll see a page that's currently hard-coded in the app.

![initial view](assets/1.png)

All text is currently editable. There's a table on the right that will grow
and shrink as you add and delete text.

Changes you make are currently not saved. This is just a demo.

To pan, drag the surface around. To increase/decrease zoom, press `ctrl+=`,
`ctrl+-` respectively. To reset zoom press `ctrl+0`.

## Hacking

To edit formatting you'll need to modify the code for the app. To do
this live without restarting the app each time, download [the driver
app](https://git.sr.ht/~akkartik/driver.love). Here's an example session
using a fork of this repo:

![making changes without restarting the app](assets/2.gif)

To publish your changes:
  * delete all files with a numeric prefix from the repo, and then
  * move all files with a numeric prefix from the [save directory](https://love2d.org/wiki/love.filesystem.getSaveDirectory)
    to the repo.

## Keyboard shortcuts

While editing text:
* `ctrl+f` to find patterns within a file
* `ctrl+c` to copy, `ctrl+x` to cut, `ctrl+v` to paste
* `ctrl+z` to undo, `ctrl+y` to redo
* `ctrl+=` to zoom in, `ctrl+-` to zoom out, `ctrl+0` to reset zoom
* `alt+right`/`alt+left` to jump to the next/previous word, respectively
* mouse drag or `shift` + movement to select text, `ctrl+a` to select all

When cursor is not in an editor:
* arrow keys pan the surface
* `shift`+arrow keys pan faster
  - `pagedown` and `pageup` are aliases for `shift+down` and `shift+up` respectively

Exclusively tested so far with a US keyboard layout. If
you use a different layout, please let me know if things worked, or if you
found anything amiss: http://akkartik.name/contact

## Known issues

* Both freewheeling apps and the driver for them currently benefit from being
  launched in terminal windows rather than by being clicked on in a desktop
  OS. See [the driver app](https://git.sr.ht/~akkartik/driver.love/src/branch/main/README.md)
  for details.

* No support yet for Unicode graphemes spanning multiple codepoints.

* No support yet for right-to-left languages.

* Undo/redo may be sluggish in editor windows containing large files. Large
  files may grow sluggish in other ways.

* If you kill the process, say by force-quitting because things things get
  sluggish, you can lose data.

* Can't scroll while selecting text with mouse.

* No scrollbars yet. That stuff is hard.

## Mirrors and Forks

This repo is a fork of [lines.love](http://akkartik.name/lines.html), an
editor for plain text where you can also seamlessly insert line drawings.
Its immediate upstream is [the template repo for freewheeling apps](https://git.sr.ht/~akkartik/template-live-editor).
Updates to it can be downloaded from the following mirrors:

* https://git.sr.ht/~akkartik/luaML.love
* https://codeberg.org/akkartik/luaML.love

Further forks are encouraged. If you show me your fork, I'll link to it here.

* https://git.sr.ht/~akkartik/driver.love - the driver app for modifying
  freewheeling apps without restarting them.
* https://git.sr.ht/~akkartik/snap.love - a graph drawing tool.

## Feedback

[Most appreciated.](http://akkartik.name/contact)