The issue is in the `ED_region_overlap_isect_` family of functions I
believe. Their purpose is to check if a coordinate is in the
"non-transparent" or opaque parts of the overlapping region.
These are getting event coordinates (in window space), converted to
region relative space (substracting region->winrct).
Comparison is in view space (through `UI_view2d_region_to_view_y`)
to account for scrolling and zooming.
The thing where it goes wrong is that we are actually comparing to
`region->v2d.tot` (this can be huge, most of it not visible), where I
think we should be comparing to `region->v2d.cur` (that is the part that
is actually visible...)
Swapping `region->v2d.tot` with `region->v2d.cur` is what this PR does.
Pull Request: https://projects.blender.org/blender/blender/pulls/146032
6536fd80fc