update-thumbnails

name	update-thumbnails
description	Capture or replace the thumbnail of a Shiny app for the gallery. Use when a tile in apps.yml or packages.yml still shows the placeholder image, or when an existing thumbnail is out of date. Opens each app in a browser that the user controls. Captures the screen at 2400x1600. Saves the file with the name of the app.

Update the gallery thumbnails

The thumbnails are in thumbnails/. Each file has the name of its application, for example genescout.png or variant-reviewer.png. Each tile in apps.yml and packages.yml records the file name in its thumbnail field. R/check.R makes sure that the file is on disk.

These applications are first-party, and most of them are not deployed. They operate at a local address such as http://127.0.0.1:3838, which identifies nothing. Therefore the file name does not come from the URL. R/thumbnail-name.R holds the URL convention of the upstream gallery, which applies only if a third-party application is added.

A tile needs a screenshot if its thumbnail field is placeholder.svg. R/check.R lists these tiles after the words "awaiting a real screenshot".

Operate R in the console of Positron or RStudio. Do not use Rscript. The capture step opens a browser window that you control by hand.

Steps

1. Find the tiles that still show the placeholder. In R:

   source("R/check.R")
   

   A person edits apps.yml and packages.yml by hand, and no script writes them. check.R gives an error if a thumbnail is absent from disk. It also reports the tiles that still use placeholder.svg. If the packages are absent, restore the renv library with renv::restore().

2. Start the application. These applications are not deployed. Operate the application locally, from its own repository, in a different R session. Write down the port number.

3. Capture the screen. Do one application at a time:

   source("R/capture.R")
   url <- "http://127.0.0.1:3838"
   b <- open_app(url)          # opens a window you can see, 2400x1600 output
   

   If the content looks too small, open the application again with a zoom value. The output stays at 2400x1600, but the content becomes larger and sharper:

   b$close(); b <- open_app(url, zoom = 2)
   

   Put the application into the view that you want. There are two methods:

   • Use the window directly. Close dialogs, select tabs, and scroll.
   • Control the window from R, for example b$Runtime$evaluate('document.querySelector("a[data-value=\\"Map\\"]").click()')

   If the application is slow, wait for it to finish. Sys.sleep(6) is sufficient for most applications.

   When the view is correct, give the file argument. Use the name of the application:

   capture_app(b, url, file = "genescout.png")
   b$close()
   

   Ask the user to look at the PNG file before you continue. The image must show an interesting view, with no spinner and no dialog.

4. Point the tile to the new file. In apps.yml or packages.yml, change the thumbnail field from placeholder.svg to the new file name. Do not change fit, unless you captured a diagram instead of a screenshot. For a diagram, set fit: contain.

5. Check the data and see the site.

   source("R/check.R")
   

   quarto preview
   

   Make sure that every card in every section shows an image.

Notes

A card crops the image to 3:2 from the top left corner, because the default fit is cover. Put the header of the application, and its most legible content, in the top left of the capture. The image does not need to be exactly 2400x1600, because CSS controls the size of the box. A capture at that size keeps the crop sharp.

check.R gives a warning for an image in thumbnails/ that no tile uses. This warning finds a rename that you applied to only one of the two places.

Capture is a manual step because an application often needs a specific tab or scroll position. Control the live session, then call capture_app().