Feature request: `arrow_shift = 1` land arrow on the surface of the node marker about graphmakie.jl HOT 2 CLOSED

I agree that this would look nice.

It is however quite hard to find the correct positions of the arrowheads a priori. The arrowheads are placed in data space, their position depends on:

• the size&shape of the node marker
• the size&shape of the arrow head

For triangular markes for example there is also a dependency on the direction. Additionally, the marker space is (per default) different from data space (i.e. the arrows and nodes won't change size if you zoom in and out of the figure). So it should also depend on

• markerspace for both arrows and node symbols and
• the relation of markerspace and dataspace (i.e. current zoom level of axis).

In presence of curvy edges, the problem becomes trickier since the relation between position on edge and distance between node and arrow marker is non-linear.

This is why I've decided to throw the nicer aesthetics out of the window and go with markers in the center of a the edges in the first place. And tbh for me this reasoning still holds and its not worth the hassle. But maybe I am missing something and if there is a relatively straight forward way of calculating those positions!

In the mean time it might be worth investigating a function which fixes this after the plot (similar to your manual approach). Something like

fig, ax, p = graphplot(...)
move_arrows_to_nodes!(p)

Under the assumption that there are some Makie internals to calculate the intersection between arrow marker and node markers on a per edge base, this data could be used to bisect the the arrow_shift parameter for each edge until the markers barely touch. Obviously this brute force method is far to inefficient to become part of the "normal" graphplot pipeline.

from graphmakie.jl.

Makes sense...

from graphmakie.jl.