Depending on file type, DOpus.LoadThumbnail(fileItem) is very slow (10+ seconds) when fileItem is located in a OneDrive folder, whether or not the file is locally available. Some file types are fine - e.g. .txt - but others such as .xlsx or .exe or .pdf are not. I have resorted to using DOpus.LoadThumbnail(fileItem,nnn) to give up after nnn milliseconds but am hoping that this is a bug rather than a limitation. There is no delay when accessing the same files from a Synology Cloud folder.
What happens when viewing the same files in Explorer in thumbnails mode?
They all show instantly. The same is true with DOpus when viewing in a lister as thumbnails.
It's not just because the script cause the thumbnails to be cached, so they're fast to load the second time, is it?
No, and it's consistent across two PCs. Opus and Explorer both show the thumbnails instantly. DOpus.LoadThumbnail(fileItem) also returns thumbnails instantly in all other folders I have tried. In the case of OneDrive folders the speed of thumbnail being returned varies by file extension but is very slow for many different filetypes which are returned immediately if the script is run against the same files which have been copied to a non-OneDrive folder.
DOpus.LoadThumbnail was causing offline files to be downloaded to generate their thumbnails.
In the next update, we'll change it so it requests thumbnails for offline files via OneDrive (etc.), similar to what the lister itself does.
Aha. That explains it, and I expect it is file size, rather than extension, that drives the delay. TIA for the fix.