---
title: "User Interaction in WebGL"
author: "Duncan Murdoch"
date: "`r format(Sys.time(), '%B %d, %Y')`"
output:
  rmarkdown::html_vignette:
    toc: yes
    fig_width: 5
    fig_height: 5
vignette: >
  %\VignetteIndexEntry{User Interaction in WebGL (updated)} 
  %\VignetteEngine{knitr::rmarkdown}
---


```{r setup, echo=FALSE, results="asis"}
source("setup.R")
set.seed(123)
```

## Introduction

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](rgl.html).

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 recommended one is to call `r linkfn("rglwidget")` to produce a "widget" which can
be embedded into your document by printing it.

The older method is described in the [Legacy WebGL Methods](legacyWebGL.html) document.  It is 
likely to be supported for some time, but is
not recommended for new projects, as
the widget method is easier for
me to maintain.

I have conducted experiments on a
third method.  This is intended to be 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.
At present it is not recommended, but that may
change in the future.

## Browser support

Most browsers now support WebGL, but in some browsers it may be disabled by
default.  See http://get.webgl.org for help on a number of
different browsers.  

## Examples

We start with a simple plot of the iris data.  We
insert a code chunk and call the `r linkfn("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.
```{r}
library(rgl)
plotids <- with(iris, plot3d(Sepal.Length, Sepal.Width, Petal.Length, 
                  type="s", col=as.numeric(Species)))
rglwidget(elementId = "plot3drgl")
```

Next we insert a button to toggle the display of the data.
```{r}
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()`:
```{r}
names(plotids)
unclass(plotids)
```

## Using `magrittr` 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`](https://CRAN.R-project.org/package=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.  For example,

```{r}
rglwidget() %>%
toggleWidget(ids = plotids["data"], label = "Data")
```


Normally the
sizing of the `rglwidget()` matches the chunk's `fig.width`
and `fig.height` settings.  Sometimes the controls
take up too much space, and you'll want to reduce
the size of the display.  You can use the `r indexfns("figWidth")` and `r indexfns("figHeight")`
in the `width` and `height` arguments to `rglwidget()`
to compute alternate heights.
For example, the chunk below requests a regular
size figure in the chunk header, but shrinks the `rglwidget()` using the `height` argument.
It also swaps the order of button and scene to illustrate how to put the control ahead of
the scene:

```{r}
toggleWidget(NA, ids = plotids["data"], label = "Data") %>%
rglwidget(controllers = ., height = 0.8*figHeight()) 
```

## Controls

We have seen how to change the contents of the plot using `r indexfns("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:
```{r}
clear3d() # Remove the earlier display

setosa <- with(subset(iris, Species == "setosa"), 
     spheres3d(Sepal.Length, Sepal.Width, Petal.Length, 
                  col=as.numeric(Species),
                  radius = 0.211))
versicolor <- with(subset(iris, Species == "versicolor"), 
     spheres3d(Sepal.Length, Sepal.Width, Petal.Length, 
               col=as.numeric(Species),
     	       radius = 0.211))
virginica <- with(subset(iris, Species == "virginica"), 
     spheres3d(Sepal.Length, Sepal.Width, Petal.Length, 
               col=as.numeric(Species),
     	       radius = 0.211))
aspect3d(1,1,1)
axesid <- decorate3d()
rglwidget() %>%
toggleWidget(ids = setosa) %>%
toggleWidget(ids = versicolor) %>%
toggleWidget(ids = virginica) %>%
toggleWidget(ids = axesid)
```

Since we skipped the `label` argument, the buttons are
labelled with the name of the variable
passed as `ids`.

`toggleWidget()` is actually a convenient wrapper for
two functions:  `r indexfns("playwidget")` and `r indexfns("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,

```{r}
rglwidget() %>%
playwidget(start = 0, stop = 3, interval = 1,
	   subsetControl(1, subsets = list(
	   			 Setosa = setosa,
	   			 Versicolor = versicolor,
	   			 Virginica = virginica,
	   			 All = c(setosa, versicolor, virginica)
	   			 )))
```

There are several other "control" functions.  

### `par3dinterpControl`

`r indexfns("par3dinterpControl")` approximates the result of `r linkfn("par3dinterp")`.

For example, the following code (similar to the `r linkfn("play3d")`
example) rotates the scene in a complex way.

```{r}
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 `r linkfn("par3dinterp")`.  Because of this,
we need to output 15 steps from `r linkfn("par3dinterpControl")`
so that the distortions of linear interpolation are not visible.  

### `propertyControl`

`r indexfns("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`

`r indexfns("clipplaneControl")` allows the user to control
the location of a clipping plane by moving a slider.  

### `vertexControl`

Less general than `r linkfn("propertyControl")` is
`r indexfns("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,

```{r}
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, objid = setosa),
	step=0.01)
```

### `ageControl`	     

A related function is `r indexfns("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.  In the original scene
we need to specify multiple colours so that the
colour is not fixed, and can be controlled by the slider.  We
also give two `ageControl` calls in a list; the first
one controls the colour of the trail, the second controls
the position of the point:

```{r}
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")
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)
```

### `matrixControl`

The final function of this type is the not-yet-implemented `matrixControl`, for setting
up multiple controls to modify a matrix, typically `userMatrix`. This is used
when complex manipulation of a matrix requires several controls.

## Low level controls

We repeat the initial plot from this document:

```{r plot3d2}
plotids <- with(iris, plot3d(Sepal.Length, Sepal.Width, Petal.Length, 
                  type="s", col=as.numeric(Species)))
subid <- currentSubscene3d()
rglwidget(elementId="plot3drgl2")
```

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: 
<button type="button" onclick="rotate(10)">Forward</button>
<button type="button" onclick="rotate(-10)">Backward</button>

We stored the subscene number that is currently active in
`subid` in the code chunk above, and use it as `r rinline("subid")`
in the script below.  `knitr` substitutes the value
`r subid` 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 rinline("subid",
                           script=TRUE)`).par3d.userMatrix.rotate(angle, 0,1,0);
      rgl.drawScene();
    };
    </script>
    
<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 rinline("subid",
                           script=TRUE)`).par3d.userMatrix.rotate(angle, 0,1,0);
      plot3d2rgl.drawScene();
    };
    </script>

## Index 

The following functions are described in this document:<br>

```{r echo=FALSE, results="asis"}
writeIndex(cols = 5)
```


