Feature request: access to layers and subplots with stable API

Context

We want to display interactive SVG elements on a plotly plot in data coordinates. In order to do this, we currently use the _fullLayout "private" API in order to get a handle to

• subplots
• clipId
• top shape layer.

We then add a new layer for positioning interactive elements right above _fullLayout._shapeUpperLayer, as seen here:

import { select as d3_select } from 'd3-selection';

export function getInteractorLayer(plotlyPlot, plot='xy') {
  // plotlyPlot is a plotly plot object, e.g. from Plotly.newPlot() or Plotly.react()
  // plot is the subplot name, e.g. 'xy', 'x2y2'
  const subplot = plotlyPlot._fullLayout._plots[plot];
  const shapelayer = plotlyPlot._fullLayout._shapeUpperLayer;
  const layer_above = d3_select(shapelayer.node().parentNode);
  // create interactor layer, if not exists:
  layer_above.selectAll("g.interactorlayer")
    .data(["interactors"])
    .enter().append("g")
    .classed("interactorlayer", true);
  const interactorlayer = layer_above.selectAll("g.interactorlayer");
  const clipid = subplot.clipId.replace(/plot$/, '');
  return { interactorlayer, subplot, clipid };
}

Request

A public interface for getting handles to subplots, the clipId, and the top shape layer (or a simple API function for creating a new top layer!)

Once we have the items above, we can create interactors on top of a plotly plot and re-render them as needed with e.g.

  plotlyPlot.on('plotly_relayout', relayout);
  plotlyPlot.on('plotly_afterplot', relayout);
  plotlyPlot.on('plotly_relayouting', relayout);

as seen in this demo: https://bmaranville.github.io/plotly-interactors/demo.html (drag the interactors around and look at the console to see the callbacks being called with the updated state of the interactor)

Comece pelo exemplo de getInteractorLayer e pelos pontos de entrada plotly_relayout, plotly_afterplot e plotly_relayouting descritos na issue. Defina uma alternativa pública ao acesso privado a _fullLayout que exponha subplots, clipId e a camada superior de shapes, ou que crie uma camada superior, e depois verifique se os interactors podem ser posicionados e renderizados novamente por meio dos callbacks demonstrados.