renderImage

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

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.

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.

Examples

## Not run: ------------------------------------
# 
# shinyServer(function(input, output, clientData) {
# 
#   # 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$plot2 <- renderImage({
#     # Read plot2's width and height. These are reactive values, so this
#     # expression will re-run whenever these values change.
#     width  <- clientData$output_plot2_width
#     height <- clientData$output_plot2_height
# 
#     # A temp file to save the output.
#     outfile <- tempfile(fileext='.png')
# 
#     png(outfile, width=width, height=height)
#     hist(rnorm(input$obs))
#     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
#   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)
# })
## ---------------------------------------------

See also

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