feat: add anchor-based zigzag bend placement via zigzag-at

Add the `zigzag-at` parameter to place the middle bend of a zigzag wire
on the axis of a referenced anchor. It overrides `zigzag-ratio`, which
now defaults to `auto` (resolving to 50%) so the two are mutually
exclusive. Accepted forms are an anchor name, any CeTZ coordinate, or
the scalar offset `(rel: <length>, to: <coord>)`.

Add the generic helpers this relies on and that other wire styles reuse:
- `normalize-scalar-offset(at, axis)` turns a scalar offset into an x or
  y offset; `normalize-zigzag-at` is a wrapper around it.
- `detect-port-side(anchor, ctx)` deduces the cardinal side a port faces
  by comparing it with its element's `.center` anchor.

Add the `zigzag-at` example.

README.md

@@ -3,7 +3,7 @@
 Circuiteria is a [Typst](https://typst.app) package for drawing block circuit diagrams using the [CeTZ](https://typst.app/universe/package/cetz) package.
 
 <p align="center">
-  <img src="./gallery/platypus.png" alt="Perry the platypus" alt="A platypus / Perry the Platypus meme made with colored rounded rectangles">
+  <img src="./gallery/platypus.png" alt="A platypus / Perry the Platypus meme made with colored rounded rectangles">
 </p>
 
 ## Examples

doc/examples.typ

@@ -71,6 +71,30 @@ wire.wire("w4", ("p6","p7"), style: "guided",
 
 ```, vertical: true)
 
+#let zigzag-at = example(
+  ```
+  // `zigzag-at` places the middle bend of a zigzag wire
+  // on the axis of a referenced anchor, overriding
+  // `zigzag-ratio`.
+  element.block(x: 0, y: 0, w: 1.5, h: 1.5, id: "src",
+    ports: (east: ((id: "o", name: "O"),),))
+  element.block(x: 3, y: -1.2, w: 1, h: 1, id: "ref",
+    fill: util.colors.pink,
+    ports: (west: ((id: "p", name: "R"),),))
+  element.block(x: 5.5, y: -2, w: 1.5, h: 1.5, id: "dst",
+    ports: (west: ((id: "i", name: "I"),),))
+  // String form: anchor name of a port.
+  wire.wire("w1", ("src-port-o", "dst-port-i"),
+            style: "zigzag",
+            zigzag-at: "ref-port-p")
+  // Ergonomic offset: shift 8pt right of ref.east.
+  wire.wire("w2", ("src-port-o", "dst-port-i"),
+            style: "zigzag",
+            zigzag-at: (rel: 8pt, to: "ref.east"))
+  ```,
+  vertical: true,
+)
+
 #let stub = example(```
 draw.circle((0, 0), radius: .1, name: "p")
 wire.stub("p", "north", name: "north", length: 1)

manual.typ

@@ -1,4 +1,4 @@
-#import "@preview/tidy:0.4.1"
+#import "@preview/tidy:0.4.3"
 #import "/src/cetz.typ": draw, canvas
 #import "src/lib.typ"
 #import "doc/examples.typ"

src/cetz.typ

@@ -1 +1 @@
-#import "@preview/cetz:0.3.4": *
+#import "@preview/cetz:0.5.2": *

src/circuit.typ

@@ -1,5 +1,5 @@
 #import "/src/cetz.typ": canvas
-#import "@preview/tidy:0.3.0"
+#import "@preview/tidy:0.4.3"
 
 /// Draws a block circuit diagram
 ///

src/util.typ

@@ -73,4 +73,45 @@
 #let valid-anchors = (
   "center", "north", "east", "west", "south",
   "north-east", "north-west", "south-east", "south-west"
-)
+)
+
+/// Normalizes a coordinate so that 2D points (x, y) are padded
+/// to (x, y, 0) as required by CeTZ's coordinate resolver.
+/// Also handles function-based and dictionary-based coordinates
+/// recursively.
+///
+/// - coord (any): A CeTZ-compatible coordinate
+/// -> any
+#let normalize-coord(coord) = {
+  if type(coord) == array {
+    if coord.len() == 2 {
+      let (a, b) = coord
+      // Raw 2D point: (x, y) -> (x, y, 0)
+      if type(a) in (int, float) and type(b) in (int, float) {
+        return (a, b, 0)
+      }
+      // Function-based coordinate: (fn, point)
+      if type(a) == function {
+        let orig = a
+        return (v => {
+          let result = orig(v)
+          if type(result) == array and result.len() == 2 {
+            let (rx, ry) = result
+            if type(rx) in (int, float) and type(ry) in (int, float) {
+              return (rx, ry, 0)
+            }
+          }
+          return result
+        }, b)
+      }
+    }
+  }
+  if type(coord) == dictionary {
+    let result = (:)
+    for (key, value) in coord {
+      result.insert(key, normalize-coord(value))
+    }
+    return result
+  }
+  return coord
+}

src/wire.typ

@@ -1,5 +1,5 @@
 #import "/src/cetz.typ": draw, coordinate
-#import "util.typ": opposite-anchor
+#import "util.typ": opposite-anchor, normalize-coord
 
 /// List of valid wire styles
 /// #examples.wires
@@ -24,29 +24,123 @@
   return (pts, anchors)
 }
 
-#let get-zigzag-wire(pts, ratio, dir) = {
+// Normalize an anchor-based placement value used by `zigzag-at`, `u-at`, and
+// the `s-at-*` family.
+//
+// `axis` selects which cartesian component the offset applies to:
+//   - `"x"` → offset in x (used when the placement fixes an x coordinate, e.g.
+//             a vertical bend line for horizontal wire flow).
+//   - `"y"` → offset in y (used when the placement fixes a y coordinate).
+//
+// Accepted forms:
+//   - `none`                              → unset; caller falls back to
+//                                           depth/ratio-based placement.
+//   - `str` / tuple / native CeTZ dict    → passed through as a CeTZ coordinate.
+//   - `(rel: <length>, to: <coord>)` with a *scalar* `rel`
+//                                         → ergonomic axial offset, rewritten
+//                                           to `(rel: (rel, 0), to: to)` for
+//                                           `axis == "x"` or
+//                                           `(rel: (0, rel), to: to)` for
+//                                           `axis == "y"`. If `rel` is already
+//                                           an array/tuple, the value is
+//                                           passed through unchanged.
+#let normalize-scalar-offset(at, axis) = {
+  if at == none { return none }
+  if type(at) == dictionary and "rel" in at and "to" in at and type(at.rel) != array {
+    let r = at.rel
+    if axis == "x" {
+      return (rel: (r, 0), to: at.to)
+    } else {
+      return (rel: (0, r), to: at.to)
+    }
+  }
+  return at
+}
+
+// Backwards-compatible wrapper: translates the old `dir` vocabulary
+// (`"vertical"` / `"horizontal"`) to the `axis` vocabulary used by
+// `normalize-scalar-offset`.
+#let normalize-zigzag-at(at, dir) = {
+  let axis = if dir == "vertical" { "x" } else { "y" }
+  return normalize-scalar-offset(at, axis)
+}
+
+// Try to deduce the cardinal side a port anchor faces by comparing its
+// position to the center of the element it belongs to. Returns none if the
+// anchor is not a port-style anchor (i.e. does not contain "-port-") or if
+// resolution fails.
+#let detect-port-side(anchor, ctx) = {
+  if type(anchor) != str { return none }
+  let sep = "-port-"
+  if not anchor.contains(sep) { return none }
+  let elmt-id = anchor.split(sep).first()
+  let port-pos = none
+  let center-pos = none
+  // coordinate.resolve panics on unknown anchors; there is no try/catch in
+  // Typst, so we assume port anchors created by add-port always come with a
+  // matching group of the same name. If not, the user must set the relevant side parameter
+  // explicitly.
+  let (_, p1) = coordinate.resolve(ctx, anchor)
+  let (_, p2) = coordinate.resolve(ctx, elmt-id + ".center")
+  port-pos = p1
+  center-pos = p2
+  let dx = port-pos.at(0) - center-pos.at(0)
+  let dy = port-pos.at(1) - center-pos.at(1)
+  if calc.abs(dx) >= calc.abs(dy) {
+    return if dx >= 0 { "east" } else { "west" }
+  } else {
+    return if dy >= 0 { "north" } else { "south" }
+  }
+}
+
+#let get-zigzag-wire(pts, ratio, dir, at: none) = {
   let start = pts.first()
   let end = pts.last()
-  let mid = if dir == "vertical" {
-    (start, ratio, (horizontal: end, vertical: ()))
-  } else {
-    (start, ratio, (horizontal: (), vertical: end))
-  }
 
-  let points = if dir == "vertical" {
+  let points
-    (
+  if at == none {
-      start,
+    // Ratio-based placement (default).
-      (horizontal: mid, vertical: ()),
+    let mid = if dir == "vertical" {
-      (horizontal: (), vertical: end),
+      (start, ratio, (horizontal: end, vertical: ()))
-      end
+    } else {
-    )
+      (start, ratio, (horizontal: (), vertical: end))
+    }
+
+    points = if dir == "vertical" {
+      (
+        start,
+        (horizontal: mid, vertical: ()),
+        (horizontal: (), vertical: end),
+        end
+      )
+    } else {
+      (
+        start,
+        (horizontal: (), vertical: mid),
+        (horizontal: end, vertical: ()),
+        end
+      )
+    }
   } else {
-    (
+    // Anchor-based placement: the middle bend segment sits on the axis
-      start,
+    // extracted from `at` via CeTZ's perpendicular operator `|-`:
-      (horizontal: (), vertical: mid),
+    //   - vertical:   middle segment at x = at.x
-      (horizontal: end, vertical: ()),
+    //   - horizontal: middle segment at y = at.y
-      end
+    points = if dir == "vertical" {
-    )
+      (
+        start,
+        (at, "|-", start),
+        (at, "|-", end),
+        end
+      )
+    } else {
+      (
+        start,
+        (start, "|-", at),
+        (end, "|-", at),
+        end
+      )
+    }
   }
   let anchors = (
     "start": start,
@@ -68,8 +162,8 @@
   
   let (ctx, p0) = coordinate.resolve(ctx, start)
   let (ctx, p3) = coordinate.resolve(ctx, end)
-  p0 = (x: p0.first(), y: p0.last())
+  p0 = (x: p0.first(), y: p0.at(1))
-  p3 = (x: p3.first(), y: p3.last())
+  p3 = (x: p3.first(), y: p3.at(1))
 
   let dx1 = margin-start
   let dx2 = margin-end
@@ -86,13 +180,13 @@
   if side-end == "east" {
     dx2 *= -1
   }
-  p1 = (p0.x + dx1, p0.y)
+  p1 = (p0.x + dx1, p0.y, 0)
-  p2 = (p3.x - dx2, p0.y)
+  p2 = (p3.x - dx2, p0.y, 0)
 
   let points = (
     start,
     (horizontal: p1, vertical: ()),
-    (horizontal: (), vertical: (0, dodge-y)),
+    (horizontal: (), vertical: (0, dodge-y, 0)),
     (horizontal: p2, vertical: ()),
     (horizontal: (), vertical: end),
     end
@@ -147,18 +241,18 @@
 
 
   // points that are closest to the edge points
-  let p1 = (p0.x + dx1, p0.y + dy1)
+  let p1 = (p0.x + dx1, p0.y + dy1, 0)
-  let p5 = (p6.x + dx2, p6.y + dy2)
+  let p5 = (p6.x + dx2, p6.y + dy2, 0)
 
 
   // middle point
   let center_x = p0.x + box_width * center_horizontal / 100%
   let center_y = p0.y + box_height * center_vertical / 100%
-  let p3 = (center_x, center_y)
+  let p3 = (center_x, center_y, 0)
 
   // setting up the points for that touch the guides
-  let p2 = (0,0)
+  let p2 = (0, 0, 0)
-  let p4 = (0,0)
+  let p4 = (0, 0, 0)
   if side-start in ("north", "south") {
     p2 = (horizontal: p3, vertical: p1)
   } else {
@@ -204,8 +298,9 @@
 /// - reverse (bool): If true, the start and end points will be swapped (useful in cases where the start point depends on the end point, for example with perpendiculars)
 /// - directed (bool): If true, the wire will be directed, meaning an arrow will be drawn at the endpoint
 /// - rotate-name (bool): If true, the name will be rotated according to the wire's slope
-/// - zigzag-ratio (ratio): Position of the zigzag vertical relative to the horizontal span (only with style "zigzag")
+/// - zigzag-ratio (auto, ratio): Position of the zigzag middle bend segment relative to the horizontal (or vertical) span, as a fraction between the two endpoints (only with style "zigzag"). Defaults to `auto`, which resolves to `50%`. Panics if combined with an explicitly set `zigzag-at`.
 /// - zigzag-dir (str): The zigzag's direction. As either "vertical" or "horizontal" (only with dstyle "zigzag")
+/// - zigzag-at (none, str, array, dictionary): Optional. Anchor-based placement of the zigzag middle bend segment (only with style "zigzag"). When set, overrides `zigzag-ratio` (which must be left at its default `auto`). The middle segment sits on the axis extracted from the given coordinate: `x` for `zigzag-dir: "vertical"`, `y` for `"horizontal"`. Accepted forms: a raw CeTZ anchor name string (e.g. `"elmt.center"` or `"elmt-port-a"`); any native CeTZ coordinate (tuple, dict such as `(rel: (dx, dy), to: anchor)`); or the ergonomic scalar-offset form `(rel: <length>, to: <coord>)`, which is rewritten to a `(dx, 0)` offset for `"vertical"` and `(0, dy)` for `"horizontal"`. See #examples.zigzag-at
 /// - dodge-y (number): Y position to dodge the wire to (only with style "dodge")
 /// - dodge-sides (array): The start and end sides (going out of the connected element) of the wire (only with style "dodge")
 /// - dodge-margins (array): The start and end margins (i.e. space before dodging) of the wire (only with style "dodge")
@@ -227,8 +322,9 @@
   guided-sides: ("east", "west"),
   directed: false,
   rotate-name: true,
-  zigzag-ratio: 50%,
+  zigzag-ratio: auto,
   zigzag-dir: "vertical",
+  zigzag-at: none,
   dodge-y: 0,
   dodge-sides: ("east", "west"),
   dodge-margins: (5%, 5%)
@@ -240,6 +336,22 @@
   if pts.len() != 2 {
     panic("Wrong number of points (got " + str(pts.len()) + " instead of 2)")
   }
+
+  // `zigzag-at` validation.
+  if zigzag-at != none {
+    if style != "zigzag" {
+      panic("wire '" + id + "': `zigzag-at` requires style: \"zigzag\" (got \""
+        + style + "\")")
+    }
+    if zigzag-ratio != auto {
+      panic("wire '" + id
+        + "': cannot combine `zigzag-at` with an explicit `zigzag-ratio`")
+    }
+  }
+  let zigzag-ratio-effective = if zigzag-ratio == auto { 50% } else { zigzag-ratio }
+
+  // Normalize user-provided coordinates: (x, y) -> (x, y, 0)
+  let pts = pts.map(normalize-coord)
   
   let stroke = (
     paint: color,
@@ -256,7 +368,12 @@
     (points, anchors) = get-direct-wire(pts)
     
   } else if style == "zigzag" {
-    (points, anchors) = get-zigzag-wire(pts, zigzag-ratio, zigzag-dir)
+    (points, anchors) = get-zigzag-wire(
+      pts,
+      zigzag-ratio-effective,
+      zigzag-dir,
+      at: normalize-zigzag-at(zigzag-at, zigzag-dir),
+    )
     
   } else if style == "dodge" {
     (points, anchors) = get-dodge-wire(

typst.toml

@@ -1,7 +1,7 @@
 [package]
 name = "circuiteria"
 version = "0.2.1"
-compiler = "0.13.1"
+compiler = "0.15.0"
 repository = "https://git.kb28.ch/HEL/circuiteria"
 entrypoint = "src/lib.typ"
 authors = [