mark: Implement barbed arrows

manual.typ

@@ -409,8 +409,9 @@ grid((0,0), (3,2), help-lines: true)
 
 #show-module-fn(draw-module, "mark")
 ```example
-line((1, 0), (1, 6), stroke: (paint: gray, dash: "dotted"))
+line((1, 0), (1, 7), stroke: (paint: gray, dash: "dotted"))
 set-style(mark: (fill: none))
+line((0, 7), (1, 7), mark: (end: "barbed"))
 line((0, 6), (1, 6), mark: (end: "<"))
 line((0, 5), (1, 5), mark: (end: ">"))
 set-style(mark: (fill: black))

src/drawable.typ

@@ -200,6 +200,21 @@
     }
   }
 
+  // TikZ style barbed arrow tip
+  let barbed() = {
+    let a = vector.sub(base, w)
+    let b = vector.add(base, w)
+    let ct = vector.add(t, vector.scale(dir, -length))
+
+    path(
+      (path-util.cubic-segment(a, t, a, ct),
+       path-util.cubic-segment(t, b, ct, b)),
+      close: false,
+      fill: none,
+      stroke: stroke
+    )
+  }
+
   let harpoon(side: "left") = {
     let s = if side == "left" {
       vector.add(base, w)
@@ -243,6 +258,8 @@
     triangle()
   } else if symbol == "<" {
     triangle()
+  } else if symbol == "barbed" {
+    barbed()
   } else if symbol == "|" {
     bar()
   } else if symbol == "<>" {

src/mark.typ

@@ -55,6 +55,8 @@
 #let calc-mark-offset(ctx, symbol, style) = {
   if symbol in ("<", ">") {
     return _triangular-mark-offset(ctx, style.width, style.length, symbol, style)
+  } else if symbol == "barbed" {
+    return _triangular-mark-offset(ctx, 0 /* The tip has angle 0 */, style.length, symbol, style)
   } else if symbol in ("left-harpoon", "right-harpoon") {
     return _triangular-mark-offset(ctx, style.width / 2, style.length, symbol, style)
   } else if symbol == "<>" {

tests/arrows/test.typ

@@ -12,7 +12,7 @@
     set-style(fill: blue, mark: (fill: auto))
     rotate(-90deg)
 
-    let marks = (">", "<", "|", "<>", "o")
+    let marks = (">", "<", "|", "<>", "o", "barbed")
     for m in marks {
         next((end: m))
     }