Make spline edges end in vertical slopes

[keyserj]

Describe your issue

Functionality was added to draw edge paths based on the output of our layout algorithm, so that we could let the algorithm create paths to avoid edge label overlap. Unfortunately, the layout output does not result in vertical slopes at the start and end points of each path. These vertical slopes often seem desirable, because they go with the top-down flow of the diagram, and without them, the edges can look a little haphazard.

Here's the "avoid edge label overlap" button:

These simple edge paths all end with arrows directly upwards, which is nice:

These edge paths based on the layout algorithm have some of their paths starting/ending at sharp angles, which is awkward:

Solution you'd like

No response

Alternatives you've considered

No response

Additional context

There's context in this elkjs issue eclipse-elk/elk#848 that discusses how the bend points for the path are intended to be interpreted. The solution mentioned there is basically what we're currently using. But it doesn't attempt to keep slopes vertical at the handles.

Technical ideas and questions

• here's the code for invoking the elkjs library to get edge path points
• here's the code for drawing the edge path from the layout algo