fillcolor gradient

[cpsievert]

To enable plots like this (via ggplotly())

[alexcjohnson]

That's a bit more complicated than marker gradients #1620

• It's connected to a colorscale with multiple stops (rather than a single color for each end of the gradient as we did for markers)
• Each trace gets a different segment of that colorscale depending on its range... though I have to say that seems a heck of a lot more useful than a purely aesthetic gradient that maps the color variation to the extent of the shape, whatever that extent happens to be (but of course if we implement this, people will ask for the aesthetic version).

Hopefully we can do it without the subpixel lines ggplot introduces there (which in fairness are nontrivial to avoid eg when constructing bar charts or colorscales)

[aiqc]

came here looking for a way to gradient my shapes.