res argument not used for text in grid graphics

[wch]

The res argument affects font sizes in base graphics, but doesn't seem to affect font sizes in grid graphics.

library(Cairo)
packageVersion('Cairo')
# [1] ‘1.5.3’

# Base graphics
CairoPNG('test-Cairo-72.png', width=250, height=250, res=72)
plot(1:10, 1:10)
dev.off()

CairoPNG('test-Cairo-144-2x.png', width=500, height=500, res=144)
plot(1:10, 1:10)
dev.off()

# Grid graphics (with ggplot2)
library(ggplot2)
Cairo('test-Cairo-ggplot2-72.png', width=250, height=250, res=72)
qplot(1:10, 1:10)
dev.off()

Cairo('test-Cairo-ggplot2-144-2x.png', width=500, height=500, res=144)
qplot(1:10, 1:10)
dev.off()

[wch]

Excellent, thanks!