vignettes/WebGL.Rmd
WebGL.Rmd## Warning in rgl.init(initValue, onlyNULL): RGL: unable to open X11 display## Warning: 'rgl.init' failed, running with 'rgl.useNULL = TRUE'.This document describes how to embed rgl scenes in HTML
documents and use embedded Javascript to control a WebGL display in an
HTML document. For more general information about rgl, see
rgl Overview.
We assume that the HTML document is produced from R markdown source
using knitr or rmarkdown. This format mixes
text with Markdown markup with chunks of R code. There is a limited
amount of discussion of other methods.
There are two ways to embed an rgl scene in the
document. The newest one is recommended: call
setupKnitr with argument
autoprint = TRUE early in the document. This will set
things up to be quite similar to the way standard 2D graphics are
included by knitr, i.e. it will detect the fact that you’ve
drawn something, and just include it automatically.
If autoprint = FALSE is used or no call is made to
setupKnitr(), an explicit call to
rglwidget will produce a “widget”
which can be embedded into your document by printing it. This document
uses that method.
Older methods (e.g. writeWebGL or various hooks) that
were used before rgl version 0.102.0 are no longer
supported.
Most browsers now support WebGL, but in some browsers it may be disabled by default. See https://get.webgl.org for help on a number of different browsers.
We start with a simple plot of the iris data. We insert a code chunk
and call the rglwidget function
with optional argument elementId. This allows later
Javascript code to refer to the image. We also save the object ids from
the plot, so that they can be manipulated later. (The first example in
Controls uses tags instead of saving the
ids.)
library(rgl)
plotids <- with(iris, plot3d(Sepal.Length, Sepal.Width, Petal.Length,
type="s", col=as.numeric(Species)))
rglwidget(elementId = "plot3drgl")elementId example.
Next we insert a button to toggle the display of the data.
toggleWidget(sceneId = "plot3drgl", ids = plotids["data"], label = "Data")The sceneId is the same as the elementId we
used in rglwidget(), the ids are the object
ids of the objects that we’d like to toggle, and the label
is the label shown on the button. To find the names in the
plotids variable, apply names() or
unclass():
names(plotids)## [1] "data" "axes" "xlab" "ylab" "zlab"
unclass(plotids)## data axes xlab ylab zlab
## 8 9 10 11 12magrittr or base pipes
It can be error-prone to set the elementId in the
rglwidget() to match the sceneId in the
toggleWidget() (or playwidget(), described
below). In the usual case where both are intended to appear together, magrittr-style
pipes can be used quite flexibly: the first argument of the control
widget accepts the result of rglwidget() (or other control
widgets), and the controllers argument of
rglwidget() accepts control widgets. In R 4.1.0, the new
base pipe operator |> should be usable in the same
way.
For example,
rglwidget() %>%
toggleWidget(ids = plotids["data"], label = "Data")If you have R 4.1.0 or greater, this should do the same:
rglwidget() |>
toggleWidget(ids = plotids["data"], label = "Data")You can swap the order of button and scene; use the
magrittr dot (or the => syntax in base
pipes) to pass the toggleWidget to rglwidget
in the controllers argument:
toggleWidget(NA, ids = plotids["data"], label = "Data") %>%
rglwidget(controllers = .) or using R 4.1.0 or later,
We have seen how to change the contents of the plot using
toggleWidget.
We can do more elaborate displays. For example, we can redo the previous
plot, but with the three species as separate “spheres” objects and
buttons to toggle them:
clear3d() # Remove the earlier display
with(subset(iris, Species == "setosa"),
spheres3d(Sepal.Length, Sepal.Width, Petal.Length,
col=as.numeric(Species),
radius = 0.211,
tag = "setosa"))
with(subset(iris, Species == "versicolor"),
spheres3d(Sepal.Length, Sepal.Width, Petal.Length,
col=as.numeric(Species),
radius = 0.211,
tag = "versicolor"))
with(subset(iris, Species == "virginica"),
spheres3d(Sepal.Length, Sepal.Width, Petal.Length,
col=as.numeric(Species),
radius = 0.211,
tag = "virginica"))
aspect3d(1,1,1)
decorate3d(tag = "axes")
rglwidget() %>%
toggleWidget(tags = "setosa") %>%
toggleWidget(tags = "versicolor") %>%
toggleWidget(tags = "virginica") %>%
toggleWidget(tags = "axes") %>%
asRow(last = 4)Since we skipped the label argument, the buttons are
labelled with the values of the tags. The asRow function is
discussed below.
toggleWidget() is actually a convenient wrapper for two
functions:
playwidget
and
subsetControl.
playwidget() adds the button to the web page (and can also
add sliders, do animations, etc.), while subsetControl()
chooses a subset of objects to display.
subsetControl
For a more general example, we could use a slider to select several subsets of the data in the iris display. For example,
rglwidget() %>%
playwidget(start = 0, stop = 3, interval = 1,
subsetControl(1, subsets = list(
Setosa = tagged3d("setosa"),
Versicolor = tagged3d("versicolor"),
Virginica = tagged3d("virginica"),
All = tagged3d(c("setosa", "versicolor", "virginica"))
)))There are several other “control” functions.
par3dinterpControl
par3dinterpControl
approximates the result of
par3dinterp.
For example, the following code (similar to the
play3d example) rotates the scene in
a complex way.
M <- r3dDefaults$userMatrix
fn <- par3dinterp(time = (0:2)*0.75, userMatrix = list(M,
rotate3d(M, pi/2, 1, 0, 0),
rotate3d(M, pi/2, 0, 1, 0)) )
rglwidget() %>%
playwidget(par3dinterpControl(fn, 0, 3, steps=15),
step = 0.01, loop = TRUE, rate = 0.5)Some things to note: The generated Javascript slider has 300
increments, so that motion appears smooth. However, storing 300
userMatrix values would take up a lot of space, so we use
interpolation in the Javascript code. However, the Javascript code can
only do linear interpolation, not the more complex spline-based SO(3)
interpolation done by
par3dinterp. Because of this, we
need to output 15 steps from
par3dinterpControl so
that the distortions of linear interpolation are not visible.
propertyControl
propertyControl
is a more general function to set the value of properties of the scene.
Currently most properties are supported, but use does require knowledge
of the internal implementation.
clipplaneControl
clipplaneControl
allows the user to control the location of a clipping plane by moving a
slider.
vertexControl
Less general than
propertyControl is
vertexControl.
This function sets attributes of individual vertices in a scene. For
example, to set the x-coordinate of the closest point in the setosa
group, and modify its colour from black to white,
setosavals <- subset(iris, Species == "setosa")
which <- which.min(setosavals$Sepal.Width)
init <- setosavals$Sepal.Length[which]
rglwidget() %>%
playwidget(
vertexControl(values = matrix(c(init, 0, 0, 0,
8, 1, 1, 1),
nrow = 2, byrow = TRUE),
attributes = c("x", "red", "green", "blue"),
vertices = which, tag = "setosa"),
step = 0.01)ageControl
A related function is
ageControl,
though it uses a very different specification of the attributes. It is
used when the slider controls the “age” of the scene, and attributes of
vertices change with their age.
To illustrate we will show a point moving along a curve. We give two
ageControl calls in a list; the first one controls the
colour of the trail, the second controls the position of the point:
time <- 0:500
xyz <- cbind(cos(time/20), sin(time/10), time)
lineid <- plot3d(xyz, type="l", col = "black")["data"]
sphereid <- spheres3d(xyz[1, , drop=FALSE], radius = 8, col = "red")
rglwidget() %>%
playwidget(list(
ageControl(births = time, ages = c(0, 0, 50),
colors = c("gray", "red", "gray"), objids = lineid),
ageControl(births = 0, ages = time,
vertices = xyz, objids = sphereid)),
start = 0, stop = max(time) + 20, rate = 50,
components = c("Reverse", "Play", "Slower", "Faster",
"Reset", "Slider", "Label"),
loop = TRUE)rglMouse
While not exactly a control in the sense of the other functions in
this section, the
rglMouse
function is used to add an HTML control to a display to allow the user
to select the mouse mode.
For example, the display below initially allows selection of particular points, but the mouse mode may be changed to let the user rotate the display for a another view of the scene.
# This example requires the crosstalk package
# We skip it if crosstalk is not available.
ids <- with(iris, plot3d(Sepal.Length, Sepal.Width, Petal.Length,
type="s", col=as.numeric(Species)))
par3d(mouseMode = "selecting")
rglwidget(shared = rglShared(ids["data"])) %>%
rglMouse()The rglShared() call used here is described
below.
Many rgl displays will contain several elements: one or
more rgl scenes and controls. Internally rgl
uses the combineWidgets function from the manipulateWidget
package.
The rgl package provides 3 convenience functions for
arranging displays. We have already met the first: the
magrittr pipe, %>%. When the display is
constructed as a single object using pipes, the objects in the pipeline
will be arranged in a single column.
The second convenience function is
asRow.
This takes as input a list of objects or a combineWidgets
object (perhaps the result of a pipe), and rearranges (some of) them
into a horizontal row. As in the toggleWidget
example, the last argument can be used to limit the
actions of asRow to the specified number of components. (If
last = 0, all objects are stacked: this can be useful if
some of them are not from the rgl package, so piping
doesn’t work for them.)
Finally,
getWidgetId
can be used to extract the HTML element ID from an HTML widget. This is
useful when combining widgets that are not all elements of the same
pipe, as in the crosstalk example below.
If these convenience functions are not sufficient, you can call
manipulateWidget::combineWidgets
or other functions from manipulateWidget for more
flexibility in the display arrangements.
crosstalk
The crosstalk
package allows widgets to communicate with each other. Currently it
supports selection and filtering of observations.
rgl can send, receive and display these messages. An
rgl display may have several subscenes, each displaying
different datasets. Each object in the scene is potentially a shared
dataset in the crosstalk sense.
The linking depends on the
rglShared
function. Calling rglShared(id), where id is
the rgl id value for an object in the current scene,
creates a shared data object containing the coordinates of the vertices
of the rgl object. This object is passed to
rglwidget in the
shared argument. It can also be passed to other widgets
that accept shared data, linking the two displays.
If a shared data object has been created in some other way, it can be
linked to a particular rgl id value by copying
its key and group properties as shown in the
example below.
# This example requires the crosstalk package.
# We skip it if crosstalk is not available.
library(crosstalk)
sd <- SharedData$new(mtcars)
ids <- plot3d(sd$origData(), col = mtcars$cyl, type = "s")
# Copy the key and group from existing shared data
rglsd <- rglShared(ids["data"], key = sd$key(), group = sd$groupName())
rglwidget(shared = rglsd) %>%
asRow("Mouse mode: ", rglMouse(getWidgetId(.)),
"Subset: ", filter_checkbox("cylinderselector",
"Cylinders", sd, ~ cyl, inline = TRUE),
last = 4, colsize = c(1,2,1,2), height = 60)If multiple objects in the rgl scene need to be
considered as shared data, you can pass the results of several
rglShared() calls in a list,
i.e. rglwidget(shared = <list>). The key values will
be assumed to be shared across datasets; if this is not wanted, use a
prefix or some other means to make sure they differ between objects.
If the same rgl id is used in more than one
rglShared() object, it will respond to messages from all of
them. This may lead to undesirable behaviour as one message cancels the
previous one.
We repeat the initial plot from this document:
plotids <- with(iris, plot3d(Sepal.Length, Sepal.Width, Petal.Length,
type="s", col=as.numeric(Species)))
subid <- currentSubscene3d()
rglwidget(elementId="plot3drgl2")plot3d2 example.
We might like a button on the web page to cause a change to the display, e.g. a rotation of the plot. First we add buttons, with the “onclick” event set to a function described below:
<button type="button" onclick="rotate(10)">Forward</button>
<button type="button" onclick="rotate(-10)">Backward</button>which produces these buttons:
We stored the subscene number that is currently active in
subid in the code chunk above, and use it as
`r subid`knitr substitutes the value when it processes the
document.
The rotate() function uses the Javascript function
document.getElementById to retrieve the
<div> component of the web page containing the scene.
It will have a component named rglinstance which contains
information about the scene that we can modify:
<script type="text/javascript">
var rotate = function(angle) {
var rgl = document.getElementById("plot3drgl2").rglinstance;
rgl.getObj(`r subid`).par3d.userMatrix.rotate(angle, 0,1,0);
rgl.drawScene();
};
</script>If we had used webGL=TRUE in the chunk header, the
knitr WebGL support would create a global object with a
name of the form <chunkname>rgl. For example, if the
code chunk was named plot3d2, the object would be called
plot3d2rgl, and this code would work:
<script type="text/javascript">
var rotate = function(angle) {
plot3d2rgl.getObj(`r subid`).par3d.userMatrix.rotate(angle, 0,1,0);
plot3d2rgl.drawScene();
};
</script>