r - ggplot2 plot background colour gradient -

this code produces first plot below:

water.height <- seq(0, 5, 1) y <- seq(0, 1500, length.out = 6) df <- data.frame(water.height, y)  library(ggplot2) ggplot(df, aes(water.height, y)) + geom_blank()+ theme_bw() 

i have photoshopped in blue background:

can produce same blue background r code?

the relevant link the ggplot2 approach given in comments. copied there:

library(grid)  g <- rastergrob(blues9, width=unit(1,"npc"), height = unit(1,"npc"),  interpolate = true)  # grid.draw(g)   library(ggplot2)  ggplot(mtcars, aes(factor(cyl))) + # add gradient background     annotation_custom(g, xmin=-inf, xmax=inf, ymin=-inf, ymax=inf) +     geom_bar() # add data layer  

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my own approach:

as usual, cannot compete simple elegance of baptiste's solutions problems grid graphics, here approach since went work:

gg.background.fill <- function(gg.plot, cols = "white", = "x") {   #does not work facets    stopifnot(which %in% c("x", "y"))   which1 <- if (which == "x") "width" else "height"    require(gridextra)    g <- ggplotgrob(gg.plot)   #g <- ggplotgrob(p)   gg <- g$grobs         findit <- vapply(gg, function(x) grepl("grid.gtree", x$name, fixed = true), true)   n1 <- getgrob(gg[findit][[1]], "grill.gtree", grep=true)$name   n2 <- getgrob(gg[findit][[1]], "panel.background.rect", grep=true)$name   gg[findit][[1]]$children[[n1]]$children[[n2]]$gp$fill <- cols   x <- gg[findit][[1]]$children[[n1]]$children[[n2]][[which]]   w <- gg[findit][[1]]$children[[n1]]$children[[n2]][[which1]]   attr <- attributes(x)   x <- seq(0 + c(w)/length(cols)/2, 1 - c(w)/length(cols)/2, length.out = length(cols))   attributes(x) <- attr   gg[findit][[1]]$children[[n1]]$children[[n2]][[which]] <- x   w <- c(w)/length(cols)    attributes(w) <- attr   gg[findit][[1]]$children[[n1]]$children[[n2]][[which1]] <- w   g$grobs <- gg   class(g) = c("arrange", "ggplot", class(g))    g } p1 <-  gg.background.fill(p, colorramppalette(c("red", "blue"))(100)) print(p1) 

p2 <-  gg.background.fill(p, colorramppalette(c("red", "blue"))(100), "y") print(p2) 

this modifies existing background might considered advantage, in contrast annotation_custom approach doesn't work faceting. more work required that.