Frédéric Brière

And here is the "after" version.

For reference, here is a "before" screen grab.

Always composite image to account for alpha transparency

Always composite image to account for alpha transparency

Always composite image to account for alpha transparency

For the record, I tried many ways of obtaining the scrollbars' thickness, and this is the only method I found that actually seems to work. If someone knowledgeable of GTK has a better solution, I'd be glad to hear it.

Account for scrollbars when resizing in panorama mode

Account for scrollbars when resizing in panorama mode