improved column layout

gallery/example1.typ

@@ -22,4 +22,10 @@ Alice <-- Bob: Another authentication Response
   import "/src/diagram.typ": *
   _seq("Bob", "Alice", comment: "bonjour", color: red)
   _seq("Alice", "Bob", comment: "ok", color: blue)
+})
+
+#chronos.diagram({
+  import "/src/diagram.typ": *
+  _seq("Alice", "Bob", comment: "This is a test")
+  _seq("Alice", "Callum", comment: "This is another test with a long text")
 })

src/renderer.typ

@@ -1,7 +1,8 @@
 #import "@preview/cetz:0.2.2": canvas, draw
 
-#let X-SPACE = 2
 #let Y-SPACE = 20
+#let PAR-PAD = (5pt, 3pt)
+#let PAR-SPACE = 10
 
 #let get-participants-i(participants) = {
   let pars-i = (:)
@@ -30,7 +31,15 @@
     }
   }
 
-  let widths = participants.slice(0, -1).map(_ => 0)
+  let widths = ()
+  for i in range(participants.len() - 1) {
+    let p1 = participants.at(i)
+    let p2 = participants.at(i + 1)
+    let w1 = measure(box(p1.display-name)).width + PAR-PAD.last() * 2
+    let w2 = measure(box(p2.display-name)).width + PAR-PAD.last() * 2
+    widths.push(w1 / 2pt + w2 / 2pt + PAR-SPACE)
+  }
+
   for cell in cells.filter(c => c.i2 - c.i1 == 1) {
     let m = measure(cell.cell)
     widths.at(cell.i1) = calc.max(
@@ -38,6 +47,18 @@
       m.width / 1pt
     )
   }
+
+  let multicol-cells = cells.filter(c => c.i2 - c.i1 > 1)
+  multicol-cells = multicol-cells.sorted(key: c => {
+    c.i1 * 1000 + c.i2
+  })
+  for cell in multicol-cells {
+    let m = measure(cell.cell)
+    widths.at(cell.i2 - 1) = calc.max(
+      widths.at(cell.i2 - 1),
+      m.width / 1pt - widths.slice(0, cell.i2 - 1).sum()
+    )
+  }
   return widths
 }
 
@@ -58,7 +79,7 @@
       p.display-name,
       name: p.name,
       frame: "rect",
-      padding: (5pt, 3pt),
+      padding: PAR-PAD,
       anchor: "south"
     )
   }
@@ -108,7 +129,7 @@
         p.display-name,
         name: p.name,
         frame: "rect",
-        padding: (5pt, 3pt),
+        padding: PAR-PAD,
         anchor: "north"
       )
     }