Image file output — renderImage

renderImage(
  expr,
  env = parent.frame(),
  quoted = FALSE,
  deleteFile,
  outputArgs = list()
)

Arguments

expr	An expression that returns a list.
env	The environment in which to evaluate expr.
quoted	Is expr a quoted expression (with quote())? This is useful if you want to save an expression in a variable.
deleteFile	Should the file in func()$src be deleted after it is sent to the client browser? Generally speaking, if the image is a temp file generated within func, then this should be TRUE; if the image is not a temp file, this should be FALSE. (For backward compatibility reasons, if this argument is missing, a warning will be emitted, and if the file is in the temp directory it will be deleted. In the future, this warning will become an error.)
outputArgs	A list of arguments to be passed through to the implicit call to imageOutput() when renderImage is used in an interactive R Markdown document.

Description

Renders a reactive image that is suitable for assigning to an output slot.

Details

The expression expr must return a list containing the attributes for the img object on the client web page. For the image to display, properly, the list must have at least one entry, src, which is the path to the image file. It may also useful to have a contentType entry specifying the MIME type of the image. If one is not provided, renderImage will try to autodetect the type, based on the file extension.

Other elements such as width, height, class, and alt, can also be added to the list, and they will be used as attributes in the img object.

The corresponding HTML output tag should be div or img and have the CSS class name shiny-image-output.

See also

For more details on how the images are generated, and how to control the output, see plotPNG().

Examples

## Only run examples in interactive R sessions
if (interactive()) {
options(device.ask.default = FALSE)

ui <- fluidPage(
  sliderInput("n", "Number of observations", 2, 1000, 500),
  plotOutput("plot1"),
  plotOutput("plot2"),
  plotOutput("plot3")
)

server <- function(input, output, session) {

  # A plot of fixed size
  output$plot1 <- renderImage({
    # A temp file to save the output. It will be deleted after renderImage
    # sends it, because deleteFile=TRUE.
    outfile <- tempfile(fileext='.png')

    # Generate a png
    png(outfile, width=400, height=400)
    hist(rnorm(input$n))
    dev.off()

    # Return a list
    list(src = outfile,
         alt = "This is alternate text")
  }, deleteFile = TRUE)

  # A dynamically-sized plot
  output$plot2 <- renderImage({
    # Read plot2's width and height. These are reactive values, so this
    # expression will re-run whenever these values change.
    width  <- session$clientData$output_plot2_width
    height <- session$clientData$output_plot2_height

    # A temp file to save the output.
    outfile <- tempfile(fileext='.png')

    png(outfile, width=width, height=height)
    hist(rnorm(input$n))
    dev.off()

    # Return a list containing the filename
    list(src = outfile,
         width = width,
         height = height,
         alt = "This is alternate text")
  }, deleteFile = TRUE)

  # Send a pre-rendered image, and don't delete the image after sending it
  # NOTE: For this example to work, it would require files in a subdirectory
  # named images/
  output$plot3 <- renderImage({
    # When input$n is 1, filename is ./images/image1.jpeg
    filename <- normalizePath(file.path('./images',
                              paste('image', input$n, '.jpeg', sep='')))

    # Return a list containing the filename
    list(src = filename)
  }, deleteFile = FALSE)
}

shinyApp(ui, server)
}