Interface LinkDrawingsAdapter

One member's side of drawing sharing, supplied by the host. Usually two lines over a draw-tier DrawingLinkGroup kept for the group:

group.add(chart, { drawings: {
  join: () => sharing.add(chart, controller),
  leave: () => sharing.remove(chart),
} });
Copy

The group calls join when the member is in it and the channel is on, and leave when either stops being true (the switch goes off, the member is removed, replaces its adapter or is destroyed, or the group is destroyed). Calls alternate: never two joins without a leave between them.

Which drawings cross, as the draw tier's DrawingLinkGroup decides it:

• Only between charts showing the same instrument, symbol and exchange. A level drawn on one stock means nothing on another, so a chart on another instrument neither sends nor receives, whatever its group.
• Only price-pane drawings in data space. A drawing pinned to the viewport is a place on this chart's screen and stays on it.
• Drawn while the channel is on, to the charts present. A drawing crosses to the charts on its instrument when it is drawn, and its edits and its deletion follow it there. A drawing that has never been shared stays private to its chart until the host shares it (DrawingLinkGroup.share), so switching the channel on never sprays one chart's levels across a desk; a chart that arrives on the instrument later gets a drawing shared without it the same way, when the host shares it again.
• An instrument change keeps drawings with their instrument. Drawings are kept per instrument (InstrumentDrawings), so a chart leaving an instrument takes its copies of the shared drawings into that instrument's saved document and shows the incoming instrument's own. When it comes back they reconnect, and take the state the charts still on it hold now, a deletion included. With symbol linking on, the whole group moves together and keeps sharing on the new instrument.
• Leaving keeps what arrived, and re-linking reconnects it. Switching the channel off, or taking a chart out of the group, stops the traffic; every copy already made stays on the chart that holds it. A copy still carries its link, so when its chart shares again (the switch goes back on, or it rejoins) it reconnects and takes the state the charts already sharing hold, as on returning to an instrument: their edits, and a deletion made while they were sharing. An edit made to a copy while unlinked therefore gives way on re-linking. Members join in the order they were added, so when the switch goes on for the whole group the first of them that holds the drawing sets its state.