Thanks for giving line.c a default gap dialog box as well. That will be convenient.
I just ran across a simple way to create an approximate center connection point for arbitrary objects: Draw a line with fractional start/end gaps=0.5 between two object corners. Then you can use the line's center connection point as if it were an object connection point. It's almost possible to do this with the traditional gapless line by drawing a white line or a zero width line between object corners. But the white line could become visible in certain situations, and zero-width lines are not quite zero width. They remain slightly visible. The gapped line, however, appears to be completely absent (as long as fractional_start_gap + fractional_end_gap = 1).
And another advantage is if you choose other fractional gaps like (0.3,0.7) or (-2,3), you can fine-tune the position of your connection point. It's even possible to use two gapped lines to create a connection point for an object anywhere in the x-y plane. The only problem is that it is a bit difficult to find and edit zero-length lines once you have them! See example.
Description: GNU Zip compressed data