[add] separation parameter to permute()

To customize (or disable) the stroke of the thicker line that is drawn below the wires to separate them

src/draw-functions.typ

@@ -179,6 +179,12 @@
   let dy = draw-params.multi.wire-distance
   let width = gate.width
   if dy == 0pt { return box(width: width, height: 4pt) }
+
+  let separation = gate.data.separation
+  if separation == auto { separation = draw-params.background }
+  if type(separation) == color { separation += 3pt }
+  if type(separation) == length { separation += draw-params.background }
+
   box(
     height: dy + 4pt,
     inset: (y: 2pt),
@@ -190,7 +196,9 @@
         let to = qubits.at(from)
         let y-from = draw-params.center-y-coords.at(from + gate.qubit) - y0
         let y-to = draw-params.center-y-coords.at(to + gate.qubit) - y0
-        place(path(((0pt,y-from), (-width/2, 0pt)), ((width, y-to), (-width/2, 0pt)), stroke: 3pt + draw-params.background))
+        if separation != none {
+          place(path(((0pt,y-from), (-width/2, 0pt)), ((width, y-to), (-width/2, 0pt)), stroke: separation))
+        }
         place(path(((-.1pt,y-from), (-width/2, 0pt)), ((width+.1pt, y-to), (-width/2, 0pt)), stroke: draw-params.wire)) 
       }
     }

src/gates.typ

@@ -178,9 +178,12 @@
 ///  
 /// - ..qubits (array): Qubit permutation specification. 
 /// - width (length): Width of the permutation gate. 
-/// 
-#let permute(..qubits, width: 30pt) = {
-  mqgate(none, n: qubits.pos().len(), width: width, draw-function: draw-functions.draw-permutation-gate, data: (qubits: qubits.pos(), extent: 2pt))
+/// - separation (auto, none, length, color, stroke): Overlapping wires are separated by drawing a thicker line below. With this option, this line can be customized in color or thickness. 
+#let permute(..qubits, width: 30pt, separation: auto) = {
+  if qubits.named().len() != 0 {
+    assert(false, message: "Unexpected named argument `" + qubits.named().keys().first() + "` in function `permute()`")
+  }
+  mqgate(none, n: qubits.pos().len(), width: width, draw-function: draw-functions.draw-permutation-gate, data: (qubits: qubits.pos(), extent: 2pt, separation: separation))
 }
 
 /// Create an invisible (phantom) gate for reserving space. If `content` 

tests/gates/permute/test.typ

@@ -4,6 +4,18 @@
 
 #quantum-circuit(
   2, permute(1,0), permute(1,0), 1, permute(2,0,1), 2, [\ ],
-  2, 4,permute(1,0), 1, [\ ],
+  2, 4, permute(1,0), 1, [\ ],
   2, gate($H$), 5,
+)
+
+#pagebreak()
+
+// Test separation parameter
+#quantum-circuit(
+  1, 
+  permute(1,0, separation: none), 
+  permute(1,0, separation: 2pt), 
+  permute(1,0, separation: red), 
+  1, [\ ],
+  5
 )