require(grDevices)

library(gridGraphics)

rect1 <- function() {
    ## set up the plot region:
    par(bg = "thistle")
    plot(c(100, 250), c(300, 450), type = "n", xlab = "", ylab = "",
         main = "2 x 11 rectangles; 'rect(100+i,300+i,  150+i,380+i)'")
    i <- 4*(0:10)
    ## draw rectangles with bottom left (100, 300)+i
    ## and top right (150, 380)+i
    rect(100+i, 300+i, 150+i, 380+i, col = rainbow(11, start = 0.7, end = 0.1))
    rect(240-i, 320+i, 250-i, 410+i, col = heat.colors(11), lwd = i/5)
    ## Background alternating  ( transparent / "bg" ) :
    j <- 10*(0:5)
    rect(125+j, 360+j,   141+j, 405+j/2, col = c(NA, 0),
         border = "gold", lwd = 2)
    rect(125+j, 296+j/2, 141+j, 331+j/5, col = c(NA, "midnightblue"))
    mtext("+  2 x 6 rect(*, col = c(NA,0)) and  col = c(NA,\"m..blue\"))")
}

rect2 <- function() {
    ## an example showing colouring and shading
    plot(c(100, 200), c(300, 450), type= "n", xlab = "", ylab = "")
    rect(100, 300, 125, 350) # transparent
    rect(100, 400, 125, 450, col = "green", border = "blue") # coloured
    rect(115, 375, 150, 425, col = par("bg"), border = "transparent")
    rect(150, 300, 175, 350, density = 10, border = "red")
    rect(150, 400, 175, 450, density = 30, col = "blue",
         angle = -30, border = "transparent")
    
    legend(180, 450, legend = 1:4, fill = c(NA, "green", par("fg"), "blue"),
           density = c(NA, NA, 10, 30), angle = c(NA, NA, 30, -30))
}

rect3 <- function() {
    plot(1:10, log="x")
    rect(2, 2, 6, 6)
}

plotdiff(expression(rect1()), "rect-1")
plotdiff(expression(rect2()), "rect-2")
plotdiff(expression(rect3()), "rect-3")

plotdiffResult()