Plotting in an interactive loop does not render all plots.

[jinlow]

Describe the bug
I have a package that has some interactivity, that depends on being able to display plots in a loop. In RStudio, all plots display, but in the vscode extension (both the base plotter, and the httpgd backend), only the first (and the last plot when you quit the loop) display.

To Reproduce
Create an R session, the following code reproduces this, but only the first plot displays interactivly.

data(mtcars)
while (TRUE) {
  cat("Enter 'p' to print a plot, and 'q' to quit.")
  command <- readLines(n=1)
  if (command == "p") {
    var = sample(colnames(mtcars), 1)
    barplot(table(mtcars[[var]]), main = var)
  }
  if (command == "q") {
    break
  }
}

Do you want to fix by self? (We hope your help!)

I do not think I have the knowledge of VScode plugins to fix this myself.

Expected behavior
I would expect all of the plots to display interactively.

Screenshots
If applicable, add screenshots to help explain your problem.
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Environment (please complete the following information):

• OS: [e.g. Windows]
• VSCode Version: [e.g. 1.60.2]
• R Version: [e.g. 4.1.1]
• vscode-R version: [e.g. 2.3.1]

[renkun-ken]

I could reproduce this. It is not related to vscode-R but how httpgd triggers plot update via interactive user input.

In a vanilla R outside vscode, run R and create an httpgd device:

httpgd::hgd()
httpgd::hgd_browse()

Then a web plot viewer is open in the browser. Run your code, and you will find that the same problem persists.

[renkun-ken]

Please file an issue at https://github.com/nx10/httpgd/issues.

[jinlow]

But this issue is present with the vscode-R extension, even when I am not using httpgd.

[renkun-ken]

But this issue is present with the vscode-R extension, even when I am not using httpgd.

vscode-R by default uses a png device replayed in the task callback on top-level user input. It is a known limitation documented at https://github.com/REditorSupport/vscode-R/wiki/Plot-viewer#png-file. Using httpgd is always recommended.

[jinlow]

Thanks @renkun-ken! That makes sense.