r1 <- rectGrob(height=.2, gp=gpar(fill="black"), name="r1")
r2 <- rectGrob(width=.2, gp=gpar(fill="grey"), name="r2")
r3 <- rectGrob(width=.4, height=.4, gp=gpar(fill="white"),
               name="r3")
gt <- gTree(children=gList(r1, r2, r3), name="gt")
grid.draw(gt)


grid.reorder("gt", c("r3", "r2", "r1"))


grid.rect(gp=gpar(col="gray"))
r1 <- rectGrob(height=.2, gp=gpar(fill="black"), name="r1")
r2 <- rectGrob(width=.2, gp=gpar(fill="grey"), name="r2")
r3 <- rectGrob(width=.4, height=.4, gp=gpar(fill="white"),
               name="r3")
gt <- gTree(children=gList(r1, r2, r3), name="gt")
grid.draw(gt)
grid.reorder("gt", c("r3", "r2", "r1"))