# `Hakushi.Kits.Ink`
[🔗](https://github.com/hattoriai/hakushi/blob/v0.6.0/lib/hakushi/kits/ink.ex#L1)

The kit of ink: drawing on the paper with a pen, over anything on the
canvas (annotate, sketch, circle a node, write by hand), with a
highlighter, an eraser of whole strokes, and a lasso that selects
strokes and nodes alike.

    <.canvas id="board" graph={@graph} kits={[Hakushi.Kits.Notes, Hakushi.Kits.Ink]} on_change={&save/2} />

The canvas gets a bar of the kit's tools (`c:Hakushi.Kit.tools/1`):
the pointer, the pen and the highlighter with their colours and widths,
the eraser and the lasso. The pen's line is smoothed as it is drawn,
thinner and thicker with a stylus's pressure, and sharp at any zoom;
when the pen lifts, its points are simplified and the stroke is a node.

A stroke is a node of type `"ink-stroke"`: its box is around the line,
and its data is the line's points, relative to the box:

    %{
      "tool" => "pen",
      "color" => "ink",
      "size" => 4,
      "points" => [[12.5, 8, 0.42], [14, 9.5, 0.5], ...]
    }

A point is `[x, y, pressure]`, the pressure from 0 to 1 (`0.5` for a
mouse). The colours are `colors/0`, the tools `"pen"` and
`"highlighter"`. A stroke moves, goes in a group (drawn over a frame,
it is in it), copies, deletes and undoes as any node, through the
rules and `on_change`; it has no handles, so no edges.

On a shared canvas, the others see a stroke as it is drawn: it goes
in the person's awareness, as a drag does, and becomes a change when
the pen lifts. An agent draws with `draw_on_canvas`
(`Hakushi.Issho.tools/0`), and the people see its pen go.

# `colors`

```elixir
@spec colors() :: [String.t()]
```

The colours of ink, in the order of the bar.

# `stroke`

```elixir
@spec stroke([Hakushi.Ink.point()], keyword()) :: {:ok, map()} | :error
```

A stroke's node, from its points on the canvas (`[x, y, pressure]` or
`[x, y]`): its box around them, and its points relative to it. Gives
`{:ok, node}`, or `:error` for points or a tool it does not draw.

Options: `:tool` (`"pen"`, the default, or `"highlighter"`), `:color`
(one of `colors/0`) and `:size` (the line's width at a pressure of
0.5), each the tool's own unless given.

    {:ok, node} = Hakushi.Kits.Ink.stroke([[0, 0], [40, 10], [80, 0]], color: "red")

---

*Consult [api-reference.md](api-reference.md) for complete listing*