I have tried to find whether there is away to prevent the document closing after the painting finish. There might be several reasons, e.g., the exported images is different from what you see during painting, the '-batch-out-rgba_canvas' option which is supposed to save all the effect doesn't work, or when I want to add some final touches after the painting ends.
The trick is to manually save the file before the document close. You can hit ctrl+S or click on the menu and click save(during the painting progress the UI is still responsive). After you hit save, the automated painting will be stopped. To make it easier, you can add a huge number of simulation steps at the end, e.g. add 10,000 simulation steps at the end so you actually have the chance to click save after the last stroke is finished.
Cheers,
JX
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