[FEATURE] Stacked Areas and Lines

[bryevdv]

Strangely, I can't find a suitable issue for this. Anyway, I will submit a PR later this week to add support for this:

Implementation is basically done, needs docs and tests. Would not mind some feedback on a couple of questions:

• The harea and varea only have fill props currently. The rationale is that AFAICT these kinds of charts never outline the sides/bottom. Does that seem reasonable?

• x1 and x2? or x0 and x1?

cc @bokeh/core @bokeh/dev @pzwang for any comments before submitting

[bryevdv]

For good measure here is how it will look horizontal or negative:

[birdsarah]

The rationale is that AFAICT these kinds of charts never outline the sides/bottom. Does that seem reasonable?

I think that's reasonable. There are certainly workarounds if we decided not to. Excited to see this.

[bryevdv]

@birdsarah do you think it would be OK to ship a first cut of this w/o working hover support? Patch does not currently support hit testing, and I am not sure what it would take to get things working well

[wabu]

Does hover work on the borders at least? Had the problem in holoviews and created an invisible lines overlay to get hover on these ...

[bryevdv]

Stacked area has no border of its own, as discussed above. But hover currently would work on a corresponding stacked line added alongside.

[birdsarah]

@birdsarah do you think it would be OK to ship a first cut of this w/o working hover support? Patch does not currently support hit testing, and I am not sure what it would take to get things working well

I did not know that patch doesn't support hit testing....that has surprised me. I got it working in this PR https://github.com/bokeh/bokeh/pull/3399/files if there's anything you can crib from that.

I'm more taken aback by the fact that we don't have hit testing on patches, than I am concerned about having it in this case.

[bryevdv]

Patches has hit-testing, Patch does not, because it's one of the weirdo glyphs that isn't actually vectorized, so will need some special casing.

[birdsarah]

Cool. Thanks! I think it's fine to move ahead....and maybe open an issue for patch hover?

[bryevdv]

OK I will push and merge a quick PR for this later today, so I can include these areas in the hatching pr