feat: allow element alignment based on ports for x analogue to y

Accept `(from: <anchor>, to: <port-id>)` for the `x` parameter of
elements, aligning the element's port with the anchor, analogous to the
existing form for `y`. Add a `ports-x` parameter for elements with
`auto-ports: false` and a `gallery/test_xalign` gallery entry.

gallery/test_xalign.typ

@@ -0,0 +1,30 @@
+// Demonstrates the `(from: <anchor>, to: <port-id>)` port-alignment shorthand
+// for the `x` parameter (analogous to the existing shorthand for `y`).
+#import "/src/lib.typ": circuit, element, util, wire
+
+#set page(width: auto, height: auto, margin: .5cm)
+
+#circuit({
+  // Anchor block: absolute placement, with a single "addr" port on its
+  // north side (auto-centred horizontally by circuiteria).
+  element.block(
+    x: 0, y: 0, w: 2, h: 1.5,
+    id: "vcemem",
+    fill: util.colors.orange,
+    ports: (north: ((id: "addr"),), east: ((id: "out"),))
+  )
+
+  // This block's "addr" port (south side) is x-aligned with vcemem's "addr"
+  // port (north side), even though B is wider than vcemem and not
+  // horizontally aligned by default.
+  element.block(
+    x: (from: "vcemem-port-addr", to: "addr"),
+    y: (rel: 2, to: "vcemem.north"),
+    w: 4.5, h: 1,
+    id: "fsm",
+    fill: util.colors.yellow,
+    ports: (south: ((id: "addr"),), east: ((id: "out"),))
+  )
+
+  wire.wire("wAddr", ("vcemem-port-addr", "fsm-port-addr"), style: "zigzag")
+})

src/elements/element.typ

@@ -21,7 +21,9 @@
 /// - draw-shape (function): Draw function
 /// - x (number, dictionary): The x position (bottom-left corner).
 ///
-///   If it is a dictionary, it should be in the format `(rel: number, to: str)`, where `rel` is the offset and `to` the base anchor
+///   If it is a dictionary, it can take one of two forms:
+///     - `(rel: number, to: str)`: `rel` is the x offset and `to` the base anchor
+///     - `(from: str, to: str)`: `from` is the base anchor and `to` is the id of the port to align with the anchor (analogous to `y`)
 /// - y (number, dictionary): The y position (bottom-left corner).
 ///
 ///   If it is a dictionary, it can take one of two forms:
@@ -41,6 +43,7 @@
 /// - stroke (stroke): Border stroke
 /// - id (str): The block id (for future reference)
 /// - auto-ports (bool): Whether to use auto port placements or not. If false, `draw-shape` is responsible for adding the appropiate ports
+/// - ports-x (dictionary): Dictionary of the ports x offsets (used with `auto-ports: false`)
 /// - ports-y (dictionary): Dictionary of the ports y offsets (used with `auto-ports: false`)
 /// - debug (dictionary): Dictionary of debug options.
 ///
@@ -60,6 +63,7 @@
   stroke: black + 1pt,
   id: "",
   auto-ports: true,
+  ports-x: (:),
   ports-y: (:),
   debug: (
     ports: false
@@ -75,8 +79,40 @@
   if w == none { panic("Parameter w must be set") }
   if h == none { panic("Parameter h must be set") }
 
-  if (type(x) == dictionary) {
+  if (type(x) == dictionary and "rel" in x) {
     x = util.resolve-rel-coord(ctx, x, 0)
+  } else if (type(x) == dictionary) {
+    let from = x.from
+    let to = x.to
+    let (to-side, i) = find-port(ports, to)
+    let margins = (0%, 0%)
+    if to-side in ports-margins {
+      margins = ports-margins.at(to-side)
+    }
+
+    let dx
+    let left-margin
+    if to-side in ("north", "south") {
+      let used-pct = 100% - margins.at(0) - margins.at(1)
+      let used-width = width * used-pct / 100%
+      left-margin = width * margins.at(0) / 100%
+
+      dx = used-width * (i + 1) / (ports.at(to-side).len() + 1)
+
+      if not auto-ports {
+        left-margin = 0
+        dx = ports-x.at(to)(width)
+      }
+    } else if to-side == "west" {
+      dx = 0
+      left-margin = 0
+    } else if to-side == "east" {
+      dx = width
+      left-margin = 0
+    }
+
+    let (ctx, from-pos) = coordinate.resolve(ctx, from)
+    x = from-pos.at(0) + dx - width + left-margin
   }
   
   if (type(y) == dictionary and "rel" in y) {