cursor position, leading/trailing and affinity

Nobody has claimed this yet.

I ran into an issue in piet-coregraphics where `hit_test_position` wasn't respecting trailing newlines, and this has led me down a bit of a rabbit hole. In particular, I'm curious that there doesn't seem to be any concept of leading/trailing or upstream/downstream here? Is this an oversight, or am I missing something?

As an illustration, imagine the text "AAA BBB" with a soft break, so lines are "AAA " and "BBB". If I hit-test position 4, both "AAA |" and "|BBB" are valid. Is there some trick I'm missing? This doesn't seem to be as much of an issue on piet-d2d, although I haven't been able to play around there quite as much.

I'm pretty sure I could implement this in piet as some kind of `cursor_pos_for_point` method, because then I could ensure I take the line of the point into account when choosing my position instead of resolving to a string index and resolving from that back to a point, which is lossy?

Start by examining hit_test_position in piet-coregraphics and comparing its behavior with piet-d2d, especially for trailing newlines and soft breaks. Review the proposed cursor_pos_for_point direction and the issue's leading/trailing or upstream/downstream questions. Done means the desired cursor-position and affinity behavior is defined clearly enough to assess across the backends.

Written by the indexing model from the issue text.