strokeWidth as a channel

[Fil]

closes #311

build : https://observablehq.com/@fil/plot-strokewidth-322

[Fil]

do you have an idea for a test plot?

[mbostock]

I think we’ll want a scale on this, no? It feels like the sort of thing you’d want a scale for, rather than specifying literal pixels. But I guess the same argument could be made for font-size.

[Fil]

Can do, but I'm not sure it's worth it. Links tend to come with value=1…10 (co-occurences as in the miserables.json example), or 0…1, or sometimes from distance matrices 0…infty, and I feel it's always more "graphic tweaking" than really using it as an encoding to be shared with another mark.

[tophtucker]

here's my recent real-world example of "stroke as scaled channel" from pairing with a friend on a correlation chart for her psych paper; stroke shows absolute value of correlation, which i just multiplied by 3: https://observablehq.com/@tophtucker/correlation-matrix-dreamcatcher

to fil's point, if i understand it — multiplying by 3 was definitely just "graphic tweaking"; it doesn't encode anything shared with another mark.

[Fil]

Related b66b618

[mbostock]

I rebased this PR to keep it alive, but I still want to think through whether there should be a scale here (if not, that’s probably fine) and whether we also need to support this on other marks (e.g., dot and line).

[Fil]

Using this for a Sankey diagram, I'll need to set the width with a scale: identity. (Doesn't mean a scale isn't going to be useful in general.)

[ryoqun]

@Fil @mbostock hi, is this going to be merged soon? :)

Also, I want tick's strokeWidth to be a channel as well.

[Fil]

See #175 and #380

[mbostock]

I support not having a scale for strokeWidth (at least for now), but it does feel arbitrary to only expose this property on the link mark. I would prefer to make this a standard channel on all marks, like we do with strokeOpacity. Even if that channel often goes unused, it’s still meaningful, and should be supported for consistency/symmetry. I might take a pass at this now.

[ryoqun]

I support not having a scale for strokeWidth (at least for now), but it does feel arbitrary to only expose this property on the link mark. I would prefer to make this a standard channel on all marks, like we do with strokeOpacity. Even if that channel often goes unused, it’s still meaningful, and should be supported for consistency/symmetry. I might take a pass at this now.

hey, I've always been fan of d3.js. thanks for moving this forward. :)

[ryoqun]

hooray! thanks for working hard on this. so, strokeWidth for all marks? cool. :)

fyi, I'm creating a nice chart like this with plot (simply put, we're debugging any performance issues for distributed computing node's consensus formulation):

And I want to use strokeWidth to embed extra scalar values into marks, instead of radius for visual conciseness and proper visual comparison (radius/area isn't cognitively easy than just width for visual measuring).

[Fil]

wow! great example, I'd be curious to see it in action if you can share it! If you want to test this branch I've updated the build at https://observablehq.com/@fil/plot-strokewidth-322 (see also https://observablehq.com/@fil/plot-early-bird)

[ryoqun]

I'd be curious to see it in action if you can share it!

yeah, I'd like to share but it's still in bad shape to share currently... needs some preparation to be published to the public..

If you want to test this branch I've updated the build at https://observablehq.com/@fil/plot-strokewidth-322 (see also https://observablehq.com/@fil/plot-early-bird)

seems to work nicely! (I applied strokeWidth to Plot.dot and Plot.tickX. I can't wait official new version release with it. :)

[Fil]

example for CHANGELOG:

Plot.dotX(d3.range(41), { strokeWidth: (d) => (1 + d) / 15 }).plot()

[enjalot]

Can do, but I'm not sure it's worth it. Links tend to come with value=1…10 (co-occurences as in the miserables.json example), or 0…1, or sometimes from distance matrices 0…infty, and I feel it's always more "graphic tweaking" than really using it as an encoding to be shared with another mark.

I didn't think about the "shared with another mark" aspect, but from the perspective of "Plot figures out how to map data space to graphic space for me and I just want to tweak the pixels" having a scale here is what I expect. It's similar to how I would think about the r channel in dots, where I usually want to impose some maximum size. That could be considered a graphic tweak but it's a pretty meaningful one.
I suppose for the same reason I also want a scale for fontSize, because without a scale I have to go outside of Plot to calculate the extent of the data and do the math that Plot would do for me in the other channels, like opacity

[Fil]

one thing I don't want is to write strokeWidth: d => d.strength > 5 ? 1 : .1 and get something different than 1 or .1 as a result, because a scale has warped the values. But if the default is identity, then we're good?