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 (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.