`guide_custom` fails to plot `gTree` grobs

[aravind-j]

When using guide_custom to plot a custom gTree grob as legend, it fails to plot the gTree while the individual component grobs are plotted.

library(ggplot2)
library(grid)


p <- ggplot(mtcars, aes(wt, mpg))


candy <- circleGrob(r = 0.1,
                    x = unit(0.5, units = "npc"),
                    y = unit(0.6, units = "npc"))
stick <- segmentsGrob(x0 = unit(0.5, units = "npc"),
                      x1 = unit(0.5, units = "npc"),
                      y0 = unit(0, units = "npc"),
                      y1 = unit(0.5, units = "npc"))
lollipop <- gTree(children = gList(candy, stick))




p + geom_point(aes(colour = factor(cyl))) +
  guides(custom = guide_custom(lollipop, title = "My lollipop"))

p + geom_point(aes(colour = factor(cyl))) +
  guides(custom = guide_custom(stick, title = "My stick"))

p + geom_point(aes(colour = factor(cyl))) +
  guides(custom = guide_custom(candy, title = "My candy"))

circle_1_1 <- circleGrob(name = "circle_1_1",
                         x = 0.5, y = 0.5, r = 0.1)
circle_1_2 <- circleGrob(name = "circle_1_2",
                         x = 0.5, y = 0.5, r = 0.05,
                         gp = gpar(fill = "red"))
circle_1 <- gTree(name = "circle_1_tree", children = gList(circle_1_1, circle_1_2))



p + geom_point(aes(colour = factor(cyl))) +
  guides(custom = guide_custom(circle_1, title = "My custom"))

p + geom_point(aes(colour = factor(cyl))) +
  guides(custom = guide_custom(circle_1_1, title = "My custom"))

p + geom_point(aes(colour = factor(cyl))) +
  guides(custom = guide_custom(circle_1_2, title = "My custom"))

[teunbrand]

You can use the width/height arguments to set the size of the lollipop, the only issue here is that there is no size to be determined from the grob itself.