Description:

when saving to eps, R fails to write anything semi-transparent.

Additional info:
* r 3.4.2-1


Steps to reproduce:



library(ggplot2)

ggplot(mtcars, aes(mpg, wt, alpha = gear)) +
geom_point()

ggsave("test.eps")
## fails to show semi-transparent dots with:

## Warning message:
## In grid.Call.graphics(C_points, x$x, x$y, x$pch, x$size) :
## semi-transparency is not supported on this device: reported only once per page

ggsave("test.pdf")
## saves normally