jsCanvas: Open JavaScript Canvas Graphics Device

In omegahat/RJSCanvasDevice: An R graphics device that produces JavaScript code to render on the JavaScript canvas in a browser

Description

This function opens a new R graphics device and becomes the active device to which graphics commands are sent. This device maps the graphical commands to JavaScript code. When the device is closed, the JavaScript is either written to a file or made available as a character vector. This JavaScript code can then be added to an HTML document and rendered on a JavaScript canvas.

Usage

jsCanvas(file = character(), dim = c(1000, 800), col = "black", fill = "transparent",
          ps = 10, wrapup = writeCode, 
          canvasId = "canvas", multiCanvas = FALSE, ...,
          runPlotCommand = !missing(file) && !is.character(substitute(file)))

Arguments

file	the name of a file or a connection object to which the generated JavaScript code will be written when the device is closed. This can be an empty vector (the default) in which case the code is not written to a file. Instead, the code can be accessed from the device. This argument can also be an R call or expression and it will be evaluated and the resulting JavaScript code returned directly. This allows one to open, plot and close the device in a single action and retrieve the JavaScript code in one operation.
dim	the dimensions to use for the HTML canvas device. These are pixels.
col	the default drawing color
fill	the default fill color
ps	the initial point size
wrapup	a function that is invoked when the device is closed. This is called with a list of containing code for each of the separate "pages" created in R, i.e. each time we call NewFrame. The content of each element of the page list is a character vector containing the JavaScript code for that page. The second argument is the file or connection to which to write the generated JavaScript code. Additional parameters passed to jsCanvas are also passed directly in this function call. The default is to call writeCode in the package. This turns the code into functions. One might want to use the code directly, e.g. to evaluate the commands rather than defining a function.
canvasId	the identifier(s) (i.e. name(s)) of the canvases on which to draw.
multiCanvas	a logical value that controls whether the functions arrange to draw on the separate canvases for each plot (TRUE) or on the same canvas (FALSE)
...	additional arguments that are passed on to the function specified by wrapup
runPlotCommand	this is a logical value that controls whether to interpret the file argument as R commands to run to create the plot or as the name of a file.

Value

If runPlotCommand is TRUE (e.g. if one passes a non-literal value for file), a charcter vector containing the generated JavaScript code is returned.

Otherwise, an object of class JavaScriptCanvasDevice is returned. This contains a reference to the C-level data structure representing the device and one can access the fields in the device and the R functions that implement the device.

Author(s)

Duncan Temple lang

References

R Internals Manual for details on graphics devices.

See Also

htmlCanvas

The RGraphics Device package.

Examples

 js.code = jsCanvas({ plot(1:10); plot(density(rnorm(100)))})

 dev = jsCanvas()
  plot(1:10)
  plot(density(rnorm(100)))
 f = getCode(dev)  # currently need to return the function before device is closed
 dev.off()
 f()


 jsCanvas("myJSCode.js")
  plot(1:10)
  plot(density(rnorm(100)))  
 dev.off()


  # This version writes to a file, but also controls the name of the
  # javascript functions - myPlot1 and myPlot2 - and arranges that
  # each of them is to draw on the canvas named plotCanvas.
  # We can then call these JavaScript functions at different times and
  # they will draw on that canvas.
  # We also inline the supporting JavaScript code.
 jsCanvas("myJSCode.js", funName = "myPlot", canvasId = 'plotCanvas',
              multiCanvas = FALSE, inlineJS = TRUE)
  plot(1:10)
  plot(density(rnorm(100)))  
 dev.off()

omegahat/RJSCanvasDevice documentation built on May 24, 2019, 1:54 p.m.