docs: Tweak R API documentation

* Minor changes to titles/description of exported R functions in
  the file canvas.R.
* Add links to `Message`, `type` and `data` in the webr::canvas() function
  documentation.

packages/webr/R/canvas.R

@@ -1,20 +1,25 @@
-#' Graphics device for webR HTML canvas element
+#' Graphics device for drawing to a HTML canvas element
 #'
 #' A graphics device that generates HTML canvas API calls and executes them on
 #' the worker thread using a JavaScript `OffscreenCanvas`. Once drawing has
 #' finished, a JavaScript `ImageBitmap` object is transmitted to the main webR
 #' thread for display.
 #'
-#' The resulting webR output messages are of type `Message` with the `type`
-#' property set as `'canvas'` and the `data` property populated with further
-#' details about the event that triggered the message.
+#' The resulting webR output messages are of type
+#' \href{./js/interfaces/WebRChan.CanvasMessage.html}{`CanvasMessage`}, with
+#' the \href{./js/interfaces/WebRChan.CanvasMessage.html#type}{`type`}
+#' property set as `'canvas'` and the
+#' \href{./js/interfaces/WebRChan.CanvasMessage.html#data}{`data`} property
+#' populated with further details about the event that triggered the message.
 #'
 #' When the graphics device creates a new page an output message is emitted with
-#' the `data` property set to `{ event: 'canvasNewPage' }`.
+#' the \href{./js/interfaces/WebRChan.CanvasMessage.html#data}{`data`}
+#' property set to `{ event: 'canvasNewPage' }`.
 #'
 #' When bitmap image data is sent to the main thread for display, a message is
-#' emitted with the the bitmap additionally included as part of the `data`
-#' property, `{ event: 'canvasImage', image: ImageBitmap }`.
+#' emitted with the the bitmap additionally included as part of the
+#' \href{./js/interfaces/WebRChan.CanvasMessage.html#data}{`data`} property,
+#' `{ event: 'canvasImage', image: ImageBitmap }`.
 #'
 #' A 2x scaling is used to improve the bitmap output visual quality. As such,
 #' the width and height of the HTML canvas element should be twice the width and
@@ -34,8 +39,12 @@ canvas <- function(width=504, height=504, pointsize=12, bg="transparent", ...) {
   .Call(ffi_dev_canvas, width, height, pointsize, bg)
 }
 
-#' Use the webR canvas device as the default graphics device
-#' @param ... Arguments to be passed to the canvas graphics device.
+#' Use the webR canvas graphics device
+#'
+#' Set R options so that the webR canvas graphics device is used as the default
+#' graphics device for new plots.
+#'
+#' @param ... Arguments to be passed to the graphics device.
 #' @export
 canvas_install <- function(...) {
   options(device = function() { webr::canvas(...) })