Verify if it is really necessary to store layer group projection buffer in XCF
Not a blocker or anything, just something which would be nice to look at. Right now, it seems that GIMP stores even the projection of the layer group, even though it can easily be recomputed.
Maybe was there a reason? E.g. it's faster to load the intermediate render as-is rather than recompute it? Or is it simply a miss?
See also this patch from Mikachu on IRC today (based on 2.8 code though): 0001-Save-some-space-for-group-layers.patch
Note: after discussing on IRC, it doesn't look like the part of the condition if a mask exists is really relevant, since we can just as well recompute the result of the mask. Mikachu says that it was just because "the loading code didn't work otherwise". Of course, maybe it changed since then. Otherwise we should just check and fix the loading code for this specific case to work fine.