How can I control the canvas size in ggplot?

Question

Consider this simple ggplot:

I drew a black edge on it, so it's easier to envision how large it is.

I don't understand why this plot is so large. There is nothing in my code telling ggplot that I want any area above or beneath the plot.

This seems to get me every time. How can I control the canvas size in ggplot?

library(ggplot2)

hex=c("#CC0000", "#90BD31", "#178CCB")    

q <- ggplot(data=NULL)
    q <- q + geom_rect(data=NULL, aes(xmin=0, xmax=1, ymin=0.5, ymax=1.5), fill=hex[1])
    q <- q + geom_rect(data=NULL, aes(xmin=1.5, xmax=2.5, ymin=0.5, ymax=1.5), fill=hex[2])
    q <- q + geom_rect(data=NULL, aes(xmin=3, xmax=4, ymin=0.5, ymax=1.5), fill=hex[3])
    q <- q + annotate("text", x=.5, y=0.1, label='Impaired', size=4)
    q <- q + annotate("text", x=2, y=0.1, label='Normal', size=4)
    q <- q + annotate("text", x=3.5, y=0.1, label='Optimal', size=4)
    q <- q + coord_fixed()
    q <- q + theme_classic()
    q <- q + theme(axis.line=element_blank(),
                   axis.text.x=element_blank(),
                   axis.text.y=element_blank(),
                   axis.ticks=element_blank(),
                   axis.title.x=element_blank(),
                   axis.title.y=element_blank(),
                   panel.background=element_blank(),
                   panel.border=element_blank(),
                   panel.grid.major=element_blank(),
                   panel.grid.minor=element_blank(),
                   plot.background=element_blank())
    q

Solution

Using the ggplot2 plot.margin and/or panel.margin theme options you should be able to control the internal margins, once you've adequately set the output dimensions of the canvas. This certainly will work for normal graphics devices and should also work within the shiny application:

library(ggplot2)
library(grid)

hex=c("#CC0000", "#90BD31", "#178CCB")    

q <- ggplot(data=NULL)
    q <- q + geom_rect(data=NULL, aes(xmin=0, xmax=1, ymin=0.5, ymax=1.5), fill=hex[1])
    q <- q + geom_rect(data=NULL, aes(xmin=1.5, xmax=2.5, ymin=0.5, ymax=1.5), fill=hex[2])
    q <- q + geom_rect(data=NULL, aes(xmin=3, xmax=4, ymin=0.5, ymax=1.5), fill=hex[3])
    q <- q + annotate("text", x=.5, y=0.1, label='Impaired', size=4)
    q <- q + annotate("text", x=2, y=0.1, label='Normal', size=4)
    q <- q + annotate("text", x=3.5, y=0.1, label='Optimal', size=4)
    q <- q + coord_fixed()
    q <- q + theme_classic()
    q <- q + theme(axis.line=element_blank(),
                   axis.text.x=element_blank(),
                   axis.text.y=element_blank(),
                   axis.ticks=element_blank(),
                   axis.title.x=element_blank(),
                   axis.title.y=element_blank(),
                   panel.background=element_blank(),
                   panel.border=element_blank(),
                   panel.grid.major=element_blank(),
                   panel.grid.minor=element_blank(),
                   plot.background=element_blank(),
                   plot.margin=unit(c(0,0,0,0), "cm"),
                   panel.margin=unit(c(0,0,0,0), "cm"))
    q