Incorrect zooming on HiDPI
My own build of the master branch (commit 080ef8a0) exposes a canvas zooming issue on a HiDPI display. Basically, everything is twice as large at 100% zoom level.
On GIMP 2.10, I can open a 1920x1080 image, and all of it will fit the screen at 100% zoom.
On 2.99.2-to-be, the same image will be rendered as if it was at 200% zoom, with all the ugly pixelization that you would expect :) I believe I've seen Eye of GNOME having the same issue, and it seems to be indeed the case: eog#63.