I need this too. I have my Email and Documents in Feng Office online webserver.
My clients send me photos to put on their website, but their photos are huge. These files load fully every time I want to see what the file is or if I want to edit description, relation, comments etc - it loads the whole photo.
I've done lots of projects where I had to add thumbnail generation, I'm thinking that you might be able to use just one new function -
"DisplayThumb(id,width,height)"
inside that function you check for existing thumb
if file is NOT jpg,png,gif etc do usual thing or do nothing. return;
if thumb filedate is older than original ID filedate then generate new thumb and save as /cache/thumbs/id_XXX_YYY.png (?) thumb generation does get complex when it comes to alpha channels.
show thumb at requested size
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Then you'd have to put that function into the columns, but I have no idea about that.