Ggplot2 plot background with rounded corners



With ggplot2 and the theme() function we can change the graph theme settings with almost any setting we like. See:

When we specifically look at plot.background within the theme setting, we can set the parameters with element_rect(), providing us with the tools to change colour, fill, etc.

However, I’m not sure how to set the parameters such that I can have rounded corners for the plot background

Any tips on achieving this?



I’ve been discussing this with someone on SO after they saw your tweet! Others might have more useful advice, but we speculated that this would probably require a ggplot2 extension that modified element_rect to include a roundedness parameter and allow for the use of grid.roundrect instead of grid.rect where roundedness was given by a user (assuming a default of zero).

In other words, not presently possible but doable with work :slightly_smiling_face:


Yeah, definitely sounds like a layout/extension situation.

@hoog10hk, you can see some existing ggplot2 extensions here:

The Extending ggplot2 vignette is probably a good place to start as far as making your own extension goes.


@ClausWilke posted this solution on SO


# make a plot with blue background
p <- ggplot(iris, aes(Sepal.Length, Sepal.Width)) + geom_point() +
  theme(plot.background = element_rect(fill = "#C4E7FF"),
        panel.background = element_blank(),
        plot.margin = margin(20, 20, 20, 20))

# switch out background grob
g <- ggplotGrob(p)
bg <- g$grobs[[1]]
round_bg <- roundrectGrob(x=bg$x, y=bg$y, width=bg$width, height=bg$height,
                          r=unit(0.1, "snpc"),
                          just=bg$just, name=bg$name, gp=bg$gp, vp=bg$vp)
g$grobs[[1]] <- round_bg

# draw both plots side by side
cowplot::plot_grid(p, g, labels = c("rectangular", "rounded"),
                   scale = 0.85, hjust = 0.5, label_x = 0.5)