R: Record and replay animations

ani.record {animation}

R Documentation

Record and replay animations

Description

These two functions use recordPlot and replayPlot to record image frames and replay the animation respectively.

Replay the animation

Usage

ani.record(reset = FALSE, replay.cur = FALSE)

ani.replay(list)

Arguments

`reset`	if `TRUE`, the recording list will be cleared, otherwise new plots will be appended to the existing list of recorded plots
`replay.cur`	whether to replay the current plot (we can set both `reset` and `replay.cur` to `TRUE` so that low-level plotting changes can be captured by off-screen graphics devices without storing all the plots in memory; see Note)
`list`	a list of recorded plots; if missing, the recorded plots by `ani.record` will be used

Details

One difficulty in capturing images in R (base graphics) is that the off-screen graphics devices cannot capture low-level plotting commands as new image files – only high-level plotting commands can produce new image files; ani.record uses recordPlot to record the plots when any changes are made on the current plot. For a graphical device to be recordable, you have to call dev.control('enable') before plotting.

ani.replay can replay the recorded plots as an animation. Moreover, we can convert the recorded plots to other formats too, e.g. use saveHTML and friends.

The recorded plots are stored as a list in .ani.env$.images, which is the default value to be passed to ani.replay; .ani.env is an invisible environment created when this package is loaded, and it will be used to store some commonly used objects such as animation options (ani.options).

Value

Invisible NULL.

Note

Although we can record changes made by low-level plotting commands using ani.record, there is a price to pay – we need memory to store the recorded plots, which are usually verg large when the plots are complicated (e.g. we draw millions of points or polygons in a single plot). However, we can set replay.cur to force R to produce a new copy of the current plot, which will be automatically recorded by off-screen grapihcs devices as new image files. This method has a limitation: we must open a screen device to assist R to record the plots. See the last example below. We must be very careful that no other graphics devices are opened before we use this function.

If we use base graphics, we should bear in mind that the background colors of the plots might be transparent, which could lead to problems in HTML animation pages when we use the png device (see the examples below).

Author(s)

Yihui Xie <http://yihui.name>

Examples

library(animation)

n = 20
x = sort(rnorm(n))
y = rnorm(n)
## set up an empty frame, then add points one by one
par(bg = "white")  # ensure the background color is white
plot(x, y, type = "n")

ani.record(reset = TRUE)  # clear history before recording

for (i in 1:n) {
    points(x[i], y[i], pch = 19, cex = 2)
    ani.record()  # record the current frame
}

## now we can replay it, with an appropriate pause between frames
oopts = ani.options(interval = 0.5)
ani.replay()

## or export the animation to an HTML page
saveHTML(ani.replay(), img.name = "record_plot")


## record plots and replay immediately
saveHTML({
    dev.control("enable")  # enable recording
    par(bg = "white")  # ensure the background color is white
    plot(x, y, type = "n")
    for (i in 1:n) {
        points(x[i], y[i], pch = 19, cex = 2)
        ani.record(reset = TRUE, replay.cur = TRUE)  # record the current frame
    }
})

ani.options(oopts)

[Package animation version 2.2 Index]