Edge: Relative coordinate shorthands are incorrect when using non-default axes

[deffi]

Describe the bug

With axes: (rtl, ttb) (instead of the default (ltr, ttb)), relative coordinate shorthand "r" moves left instead of right.

Similarly, with axes: (ltr, btt), relative coordinate shorthand "u" moves down instead of up.

One use case for axes: (ltr, btt) is to align the axes with those of CetZ (i.e., positive y pointing up), so we can switch between elastic coordinates (e.g., (2, 1)) and absolute coordinates (e.g., (2cm, 1cm)) without flipping the sign. But now, we have to flip the relative coordinate shorthands instead.

To Reproduce

#import "@preview/fletcher:0.5.7" as fletcher: diagram, node, edge

#diagram(
  debug: 3,
  edge-stroke: 1pt,
  node-stroke: 1pt,
  axes: (ltr, btt),

  node((0,0), [1]),
  edge("r,d", ["r,d"])  // Goes right, up (expected: right, down)
)

#diagram(
  debug: 3,
  edge-stroke: 1pt,
  node-stroke: 1pt,
  axes: (rtl, ttb),

  node((0,0), [2]),
  edge("r,d", ["r,d"])  // Goes left, down (expected: right, down)
)

#diagram(
  debug: 3,
  edge-stroke: 1pt,
  node-stroke: 1pt,
  axes: (ttb, ltr),

  node((0,0), [3]),
  edge("r,d", ["r,d"])  // Goes down, right (expected: right, down)
)

Expected behavior

"r"/"l"/"u"/"d" should go right/left/up/down, respectively, regardless of axes orientation. See the code above for specific examples.

Version information

typst 0.13.1 (8ace67d9)

[Jollywatt]

The reason I didn't do this from the start was because it is nice to be able to change a diagram's axes after the fact, to try new layouts, but if r/l/u/d/etc were invariant then some diagrams would break. However, I agree that the current behaviour also seems silly, so that it's probably better to fix this...