added sequences with same endpoints

gallery/example1.typ

@@ -54,3 +54,21 @@ Alice <-- Bob: Another authentication Response
   _seq("Alice", "Bob", comment: "Another authentication Request")
   _seq("Bob", "Alice", comment: "another authentication Response", dashed: true)
 })
+
+#chronos.diagram({
+  import "/src/diagram.typ": *
+  _seq("Alice", "Bob", comment: "message 1")
+  _seq("Bob", "Alice", comment: "ok", dashed: true)
+  _gap()
+  _seq("Alice", "Bob", comment: "message 2")
+  _seq("Bob", "Alice", comment: "ok", dashed: true)
+  _gap(size: 45)
+  _seq("Alice", "Bob", comment: "message 3")
+  _seq("Bob", "Alice", comment: "ok", dashed: true)
+})
+
+#chronos.diagram({
+  import "/src/diagram.typ": *
+  _seq("Alice", "Alice", comment: "On the\nright")
+  _seq("Alice", "Alice", flip: true, comment: "On the\nleft")
+})

src/diagram.typ

@@ -7,7 +7,8 @@
   comment: none,
   dashed: false,
   tip: "default",
-  color: black
+  color: black,
+  flip: false
 ) = {
   return ((
     type: "seq",
@@ -17,6 +18,7 @@
     dashed: dashed,
     tip: tip,
     color: color,
+    flip: flip
   ),)
 }
 
@@ -55,6 +57,13 @@
   ),)
 }
 
+#let _gap(size: 20) = {
+  return ((
+    type: "gap",
+    size: size
+  ),)
+}
+
 #let diagram(elements) = {
   let participants = ()
   let elmts = elements

src/renderer.typ

@@ -4,6 +4,7 @@
 #let Y-SPACE = 10
 #let PAR-PAD = (5pt, 3pt)
 #let PAR-SPACE = 10
+#let COMMENT-PAD = 8
 
 
 #let get-columns-width(participants, elements) = {
@@ -38,7 +39,7 @@
     let m = measure(cell.cell)
     widths.at(cell.i1) = calc.max(
       widths.at(cell.i1),
-      m.width / 1pt
+      m.width / 1pt + COMMENT-PAD
     )
   }
 
@@ -132,10 +133,37 @@
         )
       )
 
+      if elmt.p1 == elmt.p2 {
+        x2 = if elmt.flip {x1 - 20} else {x1 + 20}
+
         if elmt.comment != none {
           y -= measure(box(elmt.comment)).height / 1pt + 6
           draw.content(
-          (calc.min(x1, x2), y),
+            (x1, y),
+            elmt.comment,
+            anchor: if elmt.flip {"south-east"} else {"south-west"},
+            padding: 3pt
+          )
+        }
+
+        draw.line(
+          (x1, y),
+          (x2, y),
+          (x2, y - 10),
+          (x1, y - 10),
+          ..style
+        )
+        y -= 10
+
+      } else {
+        if elmt.comment != none {
+          let x = calc.min(x1, x2)
+          if x2 < x1 {
+            x += COMMENT-PAD
+          }
+          y -= measure(box(elmt.comment)).height / 1pt + 6
+          draw.content(
+            (x, y),
             elmt.comment,
             anchor: "south-west",
             padding: 3pt
@@ -147,7 +175,9 @@
           (x2, y),
           ..style
         )
+      }
       y -= Y-SPACE
+
     } else if elmt.type == "grp" {
       let m = measure(
         box(
@@ -200,6 +230,8 @@
       )
       y -= h / 2
       y -= Y-SPACE
+    } else if elmt.type == "gap" {
+      y -= elmt.size
     }
   }