improved seq arrow positioning

src/sequence.typ

@@ -61,11 +61,6 @@
     ll-lvl: lifelines.at(i2).level * LIFELINE-W / 2
   )
 
-  let ll-lvl1 = lifelines.at(i1).level * LIFELINE-W / 2
-
-  let x1 = x-pos.at(i1)
-  let x2 = x-pos.at(i2)
-
   if elmt.disable-src {
     let src-line = lifelines.at(i1)
     src-line.level -= 1
@@ -96,20 +91,29 @@
   if elmt.create-dst {
     let par = participants.at(i2)
     let m = measure(box(par.display-name))
-    x2 -= (m.width + PAR-PAD.last() * 2) / 2pt
+    let f = if i1 > i2 {-1} else {1}
+    end-info.x -= (m.width + PAR-PAD.last() * 2) / 2pt * f
     shapes += participant.render(x-pos, par, y: y)
   }
 
   end-info.ll-lvl = lifelines.at(i2).level * LIFELINE-W / 2
-  let ll-lvl2 = lifelines.at(i2).level * LIFELINE-W / 2
 
-  let f = if elmt.flip {-1} else {1}
-  if i1 <= i2 {
-    x1 += ll-lvl1 * f
-    x2 -= ll-lvl2 * f
-  } else {
-    x1 -= ll-lvl1 * f
-    x2 += ll-lvl2 * f
+  // Compute left/right position at start/end
+  start-info.insert("lx", start-info.x)
+  if start-info.ll-lvl != 0 { start-info.lx -= LIFELINE-W / 2 }
+  end-info.insert("lx", end-info.x)
+  if end-info.ll-lvl != 0 { end-info.lx -= LIFELINE-W / 2 }
+
+  start-info.insert("rx", start-info.x + start-info.ll-lvl)
+  end-info.insert("rx", end-info.x + end-info.ll-lvl)
+
+  // Choose correct points to link
+  let x1 = start-info.rx
+  let x2 = end-info.lx
+
+  if (start-info.i > end-info.i) {
+    x1 = start-info.lx
+    x2 = end-info.rx
   }
 
   let style = (
@@ -121,9 +125,17 @@
   )
 
   if elmt.p1 == elmt.p2 {
-    let x3 = x1 - ll-lvl1 + ll-lvl2
+    if elmt.flip {
+      x1 = start-info.lx
+    } else {
+      x2 = end-info.rx
+    }
 
-    x2 = if elmt.flip {x1 - 20} else {x1 + 20}
+    let x-mid = if elmt.flip {
+      calc.min(x1, x2) - 20
+    } else {
+      calc.max(x1, x2) + 20
+    }
 
     if elmt.comment != none {
       shapes += draw.content(
@@ -136,9 +148,9 @@
 
     shapes += draw.line(
       (x1, y),
-      (x2, y),
+      (x-mid, y),
+      (x-mid, y - 10),
       (x2, y - 10),
-      (x3, y - 10),
       ..style
     )
     y -= 10