geom_segment mitre/bevel with linewidth gradient and color gradient

[aavogt]

I would like to see these rectangles mitred and also filled with a color gradient. Ideally the aes(linewidth=th) case would also work, in which case each segment is a trapezoid before joining. I'm willing to write the PR. Does the current gradient-less behavior need to be available through something like geom_path(gradient=FALSE)?

ggplot(data.frame(th = seq(0, pi, length.out=12)), aes(sin(th), cos(th), col=th)) + geom_path(linewidth=5) 

[teunbrand]

If you need some kind of interpolation of paths, there already is ggforce::geom_link2() that comes very close to the effect you're looking for. It works best when lineend = 'round'.

library(ggplot2)

ggplot(data.frame(th = seq(0, pi, length.out=12)), aes(sin(th), cos(th), col=th)) + 
  ggforce::geom_link2(aes(linewidth = th), lineend = "round") 

^{Created on 2023-07-12 with reprex v2.0.2}

I'm afraid that it won't be straightforward to implement your proposal without essentially rewriting the paths part of a graphics engine. However if you're interested, Paul Murell has written a series of blogs about variable-width lines:

https://www.stat.auckland.ac.nz/~paul/Reports/VWline/vwline-intro/power-curve.html
https://www.stat.auckland.ac.nz/~paul/Reports/VWline/line-styles/line-styles.html
https://www.stat.auckland.ac.nz/~paul/Reports/VWline/offset-xspline/offset-xspline.html
https://www.stat.auckland.ac.nz/~paul/Reports/VWline/offsetbezier/offsetbezier.html

[teunbrand]

I'm going to close this as it is a limitation with the graphics system. If anyone finds an elegant solution to this, they're welcome to prepare a PR.