mode:text for regl-scatter2d

[jackparmer]

I have a few bio customers who need to display hundreds to thousands of single letter markers like in the below graph:

@dfcreative already has a great example of single-letter rendering for regl-scatter2d here:
https://dfcreative.github.io/regl-scatter2d/copyrights.html

I'd like to propose that mode: text be enabled for scattergl, but only work for single letters (for now).

Note that mode: text currently does not do anything for scattergl: https://codepen.io/plotly/pen/dmZNjM

We've tried creating graphs like the above with SVG, but for a larger number of letters, they are too slow. Here is an SVG example with a mode: text scatter trace overlaid on a heatmap trace: https://plot.ly/~jackp/18395/ (Note how long it takes to update when dragging the slider).

[etpinard]

I have my doubts about the single-letter approach. If we do so, then we would stuck with that until we make breaking API changes. @dfcreative How hard would it be to support text of all lengths?

And by the way @jackparmer about https://plot.ly/~jackp/18395/ are you unhappy about the first-render performance or just the drag hangups (or both 😏 )? Simply improvement drag performance for SVG text nodes shouldn't be too hard.

[jackparmer]

are you unhappy about the first-render performance or just the drag hangups (or both 😏 )

Mostly the drag performance.

How hard would it be to support text of all lengths?

Dima told me up to 2 weeks.

[dy]

@etpinard depends on the requirements. There are many ways to do that, the simplest is canvas2d texture, that may take a day or two, not guaranteed it will be fast. Font-texture or something with sdf would take a week or two. Same for vector-based approach.

There is no reliable components for doing full-featured font rendering in webgl so far. The nicest approach is in thetamath, but that is written in glslx and skew-lang.

[jackparmer]

I think we should do the sdf method after splom if we want multi-character marker text in scattergl. No point in adding mode: text to scattergl if it's not going to be significantly faster than SVG scatter.

[etpinard]

Related: #1116

[etpinard]

done in #2737, followup in #2780