Generic line shortening

[janosh]

it's already possible to use mark: (offset: <offset>) to shorten lines with marks.
but you can't shorten arbitrary unmarked lines. would be nice to have a generic shorten option on line

Originally posted by @johannes-wolf in #788 (comment)

[knuesel]

Another possibility would be to honor the offset even when the symbol is none:

#import "@preview/cetz:0.3.2"

#cetz.canvas({
  import cetz.draw: *
  line((0, 0), (4, 0))
  // Doesn't work, but this could be fixed?
  line((0, -1), (4, -1), mark: (end: none, offset: 1cm))
  // Works but ugly:
  line((0, -2), (4, -2), mark: (end: ">", offset: 1cm, scale: 0))
})

But I guess having a shorten option on paths would be cleaner. It could take a value (number or ratio) or a dict (start: ..., end: ...).

Edit: I'm not sure honoring the offset when the symbol is none would be a good idea: if the user does line((0, 0), (4, 0), mark: (end: ">", offset: 1cm)), the start mark is none, and it probably should not be shortened. So a shorten option seems like a better solution to me.