This document describes how to use embedded Javascript to control a WebGL display in an HTML document. For more general information, see rgl Overview.
We start with two simple examples. The next section gives reference information.
Consider the simple plot of the iris data. We insert a code chunk with label plot3d
(which will be used below).
with(iris, plot3d(Sepal.Length, Sepal.Width, Petal.Length,
type="s", col=as.numeric(Species)))
subid <- currentSubscene3d()
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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
in the script below.`r subid`
The rotate()
function makes use of the global <prefix>rgl
object. The knitr
WebGL support sets the prefix to the code chunk label, so the global is called plot3drgl
:
<script type="text/javascript">
var rotate = function(angle) {
plot3drgl.userMatrix[`r subid`].rotate(angle, 0,1,0);
plot3drgl.drawScene();
}
</script>
We can also change the contents of the plot using toggleButton
. For example, we can redo the previous plot, but with the three species as separate “spheres” objects and buttons to toggle them:
sphereid <- with(subset(iris, Species == "setosa"),
spheres3d(Sepal.Length, Sepal.Width, Petal.Length,
col=as.numeric(Species),
radius = 0.211))
with(subset(iris, Species == "versicolor"),
spheres3d(Sepal.Length, Sepal.Width, Petal.Length,
col=as.numeric(Species),
radius = 0.211))
with(subset(iris, Species == "virginica"),
spheres3d(Sepal.Length, Sepal.Width, Petal.Length,
col=as.numeric(Species),
radius = 0.211))
aspect3d(1,1,1)
decorate3d()
subid <- currentSubscene3d()
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toggleButton(sphereid, label = "setosa", prefix = "toggle", subscene = subid)
toggleButton(sphereid+1, label = "versicolor", prefix = "toggle", subscene = subid)
toggleButton(sphereid+2, label = "virginica", prefix = "toggle", subscene = subid)
Note that we need to use results="asis"
for the button code.
Normally we would also use echo=FALSE
, though I didn’t do so above; then the buttons will end up side-by-side:
An alternate control to achieve the same thing is subsetSlider
.
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subsetSlider(subsets = list(setosa = sphereid,
versicolor = sphereid + 1,
virginica = sphereid + 2,
all = sphereid + 0:2),
prefixes = "slider", subscenes = subid,
init = 3)
There are several other functions to generate the Javascript code for controls. par3dinterpSetter
generates a function that approximates the result of par3dinterp
. propertySetter
is a more general function to set the value of properties of the scene. Both generate Javascript functions, but not the controls to use them; for that, use propertySlider
or your own custom code.
play3d
example) rotates the scene in a complex way.
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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) ) )
propertySlider(setter = par3dinterpSetter(fn, 0, 1.5, steps=15,
prefix = "userMatrix",
subscene = subid),
step = 0.01)
Some things to note: The generated Javascript slider has 150 increments, so that motion appears smooth. However, storing 150 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 par3dinterpSetter
so that the distortions of linear interpolation are not visible.
Another function that auto-generates Javascript code is clipplaneSlider
. This function allows the user to control the location of a clipping plane by moving a slider. Both it and par3dinterpSetter
are implemented using the more general propertySlider
, which allows control of multiple objects in multiple scenes, but which does require knowledge of the internal representation of the scene in its Javascript implementation.
The final function of this type is ageSetter
. It is used when the slider controls the “age” of the scene, and attributes of vertices change with their age. For example, to show a point moving along a curve, we could do the following.
Note that we need to specify multiple colours in the plot so that the colour is not fixed, and can be controlled by the slider. We also give two ageSetter
calls in a list; the propertySlider
will control both of them simultaneously.
time <- 0:500
xyz <- cbind(cos(time/20), sin(time/10), time)
lineid <- plot3d(xyz, type="l", col = c("black", "black"))["data"]
sphereid <- spheres3d(xyz[1, , drop=FALSE], radius = 8, col = "red")
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propertySlider( list(ageSetter(births = time, ages = c(0, 0, 50),
colors = c("gray", "red", "gray"),
objids = lineid, prefixes = "curve"),
ageSetter(births = 0, ages = time,
vertices = xyz, objids = sphereid,
prefixes = "curve")),
maxS = max(time) + 50)
rgl
allows user defined mouse controls. For these to work within WebGL, you will need to write a Javascript version as well as the R version. This isn’t easy: R provides a lot of support functions which are not easily available in Javascript.
TODO: write a simple mouse control.
rglClass
In writing the writeWebGL()
function, I haven’t tried to prevent access to anything. On the other hand, I haven’t provided access to everything. The parts documented here should remain relatively stable (unless indicated otherwise). Users may also consult the source to writeWebGL
, but should be aware that anything that isn’t documented here is subject to change without notice.
As documented in writeWebGL
, the call
writeWebGL(..., prefix = "<prefix>")
will create a global object on the output page with name <prefix>rgl
and Javascript class rglClass
. This class has a large number of properties and methods, some of which are designed to be available for use by other code on the web page.
Most of the properties are stored as Javascript Array
objects, indexed by the rgl
id of the subscene to which they apply. There are also Javascript methods attached to the rglClass
class.
After any change that will affect the display, code should call <prefix>rgl.drawScene()
to redraw the scene.
inSubscene()
, addToSubscene()
, delFromSubscene()
These methods each take two arguments: id
and subscene
, which should be the rgl
ids of an object and a subscene. inSubscene
tests whether id
is already included in the subscene, and the others add it or delete it from the subscene.
This function takes a subscene id as argument, and returns an Array
containing all of the ids displayed in that subscene.
This takes an Array
of ids and a subscene id as arguments, and sets the contents of the subscene to the ids.
FOV
, listeners
, userMatrix
, zoom
These correspond to the par3d
properties with the same names.
FOV
and zoom
are arrays of numbers.userMatrix
is an array of CanvasMatrix4
objects (documented in the file system.file("WebGL/CanvasMatrix.src.js")
.listeners
item is itself an array of subscene ids that “listen” to mouse actions, i.e. listeners[19]
would contain all subscene ids that respond to mouse actions in subscene 19.This property also corresponds to the par3d
property, but should be considered to be read-only.
These two arrays contain the code to display each object in the scene. The functions in the drawFns
array are called for each object each time it is displayed. The clipFns
functions are called when objects being clipped are drawn.
Most of the data about each object in a scene is contained in the values
property. This is an array, indexed by object id. The individual entries are numeric arrays. Though they are singly-indexed, the entries are meant to be interpreted as matrices stored by row. The first 3 columns are generally the coordinates of a vertex, and remaining columns correspond to other values from rgl.attrib
.
The offsets
property gives the (0-based) offset of the first column for a particular attribute in a named object. Not all columns will be present in every object; if not present, the corresponding offsets
entry will be -1
. The entries are
Name | Meaning |
---|---|
vofs | Offset to 3 columns of vertex data in XYZ order |
cofs | Offset to 4 columns of colour data in RGBA order |
nofs | Offset to 3 columns of normal data |
radofs | Offset to 1 column of sphere radius data |
oofs | Offset to 2 columns of text or sprite origin data |
tofs | Offset to 2 columns of texture coordinates |
stride | Total number of columns in values |
For example, to find the blue colour entry for vertex i
in an object, one would first check if offsets["cofs"]
was -1
, indicating that no colour information was present. If not, the entry could be found using
values[offsets["stride"]*(i-1) + offsets["cofs"] + 2]
This assumes i
is specified using 1-based vertex counting as in R, and writes values
and offsets
instead of the fully specified <prefix>rgl.values
and <prefix>rgl.offsets
for clarity.
Changes to values
need to be pushed to the graphics system to be reflected in the scene; see the calls to gl.bindBuffer
and gl.bufferData
in the source to propertySlider
for details.
The following functions and rglClass
properties and methods are described in this document: