Enable more styling options for guide_colorbar().

[clauswilke]

Inspired by StackOverflow questions here and here: This patch enables better styling of the colorbar guide.

Examples:

set.seed(123)
df <- data.frame(x <- rnorm(10),
                 y <- rnorm(10),
                 fill <- rnorm(10))

p <- ggplot(df, aes(x, y, fill = fill)) + geom_point()

# current ggplot2
p + scale_fill_gradient(low = 'white', high = 'red')

# make frame around color bar
p + scale_fill_gradient(low = 'white', high = 'red',
                        guide = guide_colorbar(frame.colour = "black"))

# style tick marks
p + scale_fill_gradient(low = 'white', high = 'red',
                        guide = guide_colorbar(ticks.colour = "black"))

# style frame and tick marks at the same time, change linewidth
p + scale_fill_gradient(low = 'white', high = 'red',
                        guide = guide_colorbar(frame.colour = "black",
                                               frame.linewidth = 1,
                                               ticks.colour = "black",
                                               ticks.linewidth = 1))

This pull request will require some modifications once #2415 is integrated (or vice versa). I'm happy to take care of that.

[hadley]

Some minor style stuff, and a question about the argument names, but otherwise good to go.

[hadley]

Can you mention the argument names here please?

[hadley]

Have we used linewidth and linetype in other functions?

[clauswilke]

linetype is a standard aesthetic, so I think that's fine. linewidth is usually called size throughout the rest of ggplot2. If you prefer size I'm happy to make the change, it's just that frame.size doesn't sound like it controls the thickness of the frame.

[hadley]

I don't have any particularly strong feelings here; I don't really understand how these options are supposed to fit in with the theme system.

[clauswilke]

Not sure. The question is whether every possible option to a guide function needs a theme equivalent. My personal opinion is no. I think there is a lot of room for improvement for making guide functions more flexible, and possibly providing different ones or frameworks for extending them, and it's impossible to add new theme components every time somebody makes some minor tweak to some guide function. Already, there are things the guide functions can do that the theme can't control, such as the draw.ulim option for guide_colorbar().

[hadley]

Agreed. I'm happy to merge this PR; I just wanted to make sure we at least talked over the issues.

[hadley]

Would you mind adhering to modern tidyverse style here?

grobTree(
  grob.bar,
  rectGrob(
    width = barwidth.c, height = barheight.c, default.units = "mm",
    gp = gpar(
      col = guide$frame.colour,
      lwd = guide$frame.linewidth,
      lty = guide$frame.linetype,
      fill = NA
    )
  )
)

or similar

[clauswilke]

Sure, will do.

[hadley]

And here

[clauswilke]

Just a note: I'll wait with finalizing this PR until after #2415 is integrated, since they touch the same files.

[clauswilke]

I believe this latest update addresses all concerns. I added two minimal visual tests, one for the default styling (it also tests that colors can be changed via scale_color_..., so is useful anyways I think) and one for the modified styling of both the frame and the tick lines.

[hadley]

Thank you!

[lock]

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