gcanvas: Interface to canvas device

In gWidgetsWWW: Toolkit implementation of the gWidgets API for use with web pages

Description

This function allows the canvas package to create a javascript device. Although this isn't working with all browsers, it does work quite well with firefox.

Usage

gcanvas(f, width=480, height=400, container = NULL, ...)

Arguments

f	optional filename storing canvas output
width	width of canvas in pixels
height	height of canvas in pixels
container	parent container for processing object
...	not used

Details

Jeffrey Horner's canvas package provides a javascript implementation of an R device. The use if very similar to a regular, non-interactive R device, such as png. The gcanvas widget provides the screen space to display the graphic.

The svalue<- method is used to update the graphic. By default the background color for a canvas device is transparent, so graphs will layer on top of each other. To avoid this, specify a background color using hex notation, e.g., bg="#ffffff" for white.

Only one gcanvas widget can be used in a GUI, as underlying the canvas javascript is a fixed variable name. This includes subwindows of a GUI, so this is a poor choice for using in a window that can be dismissed and re-opened.

Both the gcanvas constructor and the canvas device have width and height arguments. These should be the same, but it is up to the user to ensure this.

This replaces the gprocessingjs widget that isn't working as of version 0.8.0

Value

Returns a proto object with class gCanvas.

Author(s)

John Verzani

References

The canvas device package

Examples

## Not run: 
  require(canvas, quietly=TRUE, warn=FALSE) ## require quietly

  ## Make a simple graph
  f <- tempfile() ## A file to store the javascript code
  canvas(file=f, width=480, height=400)
  hist(rnorm(100))
  dev.off()  ## write javascript code to f

  w <- gwindow("Canvas test")
  g <- ggroup(cont = w, horiz=F)
  cv <- gcanvas(f,cont = g)  ## when f is given, graph an initial graph
                             ## is drawn
  ## How to update the graphic using the svalue method
  b <- gbutton("click me", cont = g, handler = function(h,...) {
    canvas(file=f, width=480, height=400, bg="#ffffff") ## specify a
                                                        ## background color
    hist(rexp(100))
    dev.off()
    svalue(cv) <- f
  })


## End(Not run)

gWidgetsWWW documentation built on May 2, 2019, 4:47 p.m.