R Under development (unstable) (2025-07-22 r88445 ucrt) -- "Unsuffered Consequences"
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> library(grid)
> library(lattice)
> library(gridSVG)

Attaching package: 'gridSVG'

The following objects are masked from 'package:grid':

    linearGradient, pattern, radialGradient

The following object is masked from 'package:grDevices':

    dev.off

> 
> postscript(width=8, height=6, paper="special")
> 
> # Some default settings
> pushViewport(viewport(gp=gpar(col="black", fill=NA)))
> 
> y <- 1:4
> x <- 1:4
> g <- factor(c("Earth", "Moon", "Jupiter", "Mars"))
> 
> n <- 30
> d <- 20 # metres
> k <- c(9.8, 1.6, 24.8, 3.7) # gravities
> times <- 2 * sqrt(d/k) # (twice) the time taken to fall d metres
> 
> cx <- unit(rep(0.5, 2*n - 1), "npc")
> dy <- 10*seq(0, 2, length=n)^2
> ecy <- unit(40 - c(dy, rev(dy)[-1]), "native")
>   
> ballpanel <- function(x, y, subscripts) {
+   pushViewport(viewport(yscale=c(-10, 50)))
+   grid.rect(y=unit(0, "npc"), 
+             height=unit(10, "native"),
+             just="bottom",
+             gp=gpar(fill="grey"))
+   duration <- switch(subscripts,
+                      times[1],
+                      times[2],
+                      times[3],
+                      times[4])
+   col <- switch(subscripts,
+                 "blue", "grey", "brown", "red")
+   grid.circle(name=col,
+               x=cx[1],
+               y=ecy[1],
+               # r=unit(2, "mm"),
+               r=unit(1, "native"),
+               gp=gpar(col="black", fill=col))
+   grid.animate(col, x=cx, y=ecy, duration=duration, rep=TRUE)
+   if (subscripts == 1) {
+     grid.text("20 metres", 
+               x=unit(-1, "lines"), 
+               y=unit(20, "native"), 
+               just="bottom", rot=270)
+     grid.lines(x=unit(-1, "lines"),
+                y=unit.c(unit(0, "native"),
+                         unit(20, "native") - 
+                         unit(0.5, "strwidth", "40 metres") - 
+                         unit(2, "mm")))
+     grid.lines(x=unit(c(-.75, -1.25), "lines"),
+                y=unit(0, "native"))
+     grid.lines(x=unit(-1, "lines"),
+                y=unit.c(unit(40, "native"),
+                         unit(20, "native") + 
+                         unit(0.5, "strwidth", "40 metres") + 
+                         unit(2, "mm")))
+     grid.lines(x=unit(c(-.75, -1.25), "lines"),
+                y=unit(40, "native"))
+   }
+   popViewport()
+ }
> 
> print(xyplot(y ~ x | g, subscripts=TRUE,
+              layout=c(4, 1),
+              xlab=NULL, ylab=NULL,
+              panel=ballpanel,
+              scales=list(draw=FALSE)),
+       position=c(0.1, 0.1, 0.9, 0.9),
+       newpage=FALSE)
> 
> popViewport()
> 
> grid.export("ball.svg")
> 
> dev.off()
null device 
          1 
> 
> proc.time()
   user  system elapsed 
   1.62    0.04    1.67