Partitioning visualizations - improvement ideas

[monfera]

This is a set of improvements for the partitioning charts introduced with #493

• accessibility
• consider adding either more structure to the config (like linkLabel, which is already nested) - or alternatively, rely on a flatter structure for composable configurability
• review types for improvement opportunities
• outside link label improvements: value display; length limitation;
• outside link label improvements: avoidance of truncation due to chart port size
• feed styling from Theme, for what's possible and suitable refactor(partition): remove config in favor on spec and theme controls #1402
• break up long functions eg. shapeViewModel
• add unit tests
• check results in the legacy browser
• pointer events
• further work on Pie/sunburst chart - discussion about small slices #381 Provide dimension lookup in a star/snowflake schema style #464 Handling colors #492

[wylieconlon]

I have found some problems/issues as well:

• Missing legend and tooltip Partitioning visualizations - improvement ideas #518
• All of the configuration callback functions need specific type arguments, not Datum. For example, fillColor is a function called with the argument of type ShapeTreeNode, not of type Datum. This applies to the formatter functions too, like valueFormatter
• Multi-layer treemaps should support labels outside the rectangle, like this: https://www.d3-graph-gallery.com/graph/treemap_custom.html
• Text is always displayed at the top of the slice, can it be centered?

[wylieconlon]

A new piece of feedback from elastic/kibana#55477:

Not reporting the percentages and only showing the values is a concern. A pie chart is about percentages. In addition, it is helpful to have the actual value but I'm afraid without percentages it loses meaning. Ideally, we show the percentage on the slices by default and show the actual number on the tooltip.

Converting to percentages is currently done by visLib, so this seems like a responsibility of elastic-charts as well.

[monfera]

Thanks @wylieconlon, good discussion here and in the referred Lens item.

On some of the items:

• planning to add direct support for percentages this week (CD today) cc @markov00 -it's already possible to show percentages by specifying the table values as percentages, because ratios are additive, so the more aggregated sectors of a sunburst will still be correct (formatting needs to add the % sign) but dedicated support is better, as there's flexibility about showing both the percentage and the value in the tooltip if needed
• missing tooltip was what I meant by item 9; it's in progress, Marco took on the more laborious part of uncoupling the tooltip from Cartesians, and likely the legends need to be uncoupled too
• I'll check the type, which changed indeed
• treemap labeling:
  • it's planned that the multilayer treemap gets labels in the grooves; in the meantime,
  • the non-leaf layer legends should be disabled (returning the empty string), as, especially without formatting like in the storybook items, it doesn't look good
  • as a substitute, a less optimal multirow text can be used for integration testing, ie. each leaf recapitulates the higher group names too, like some Tableau example shows (Jan 31 in the charts channel)
  • for two-layer treemaps, or generally, for one of the non-leaf layers in a multilayer treemap, the color channel is the most popular method of identifying groups (categories), it requires the legend though
• re text centering, there are some tradeoffs, on tests it significantly limit the maximum possible font size or smallest labelable pie (we run out of our ability to place text inside at a larger slice than otherwise), while I realize it could make sense for short text and value combinations - other internal suggestions came up too, eg. rounding the treemap corners, or left-aligning multirow treemap texts