Reversed Mark Anchors (#724)

* mark: Fix mark anchor positioning

* tests: Update ref images

* mark: Add reversed mark anchor test

* Fix triangle mark tip anchor

* PR Fixups

src/mark-shapes.typ

@@ -49,11 +49,15 @@
 
   import "/src/draw.typ": *
   if style.reverse {
-    anchor("tip", tip)
+    // Since tip and base are now "swapped", we add the stroke thickness to the triangle
+    // base. To get smooth looking connections between the triangle tip and a connecting line,
+    // we do not add the tip-offset.
+    anchor("tip", vector.add(tip, vector.scale(dir, style.stroke.thickness / 2)))
+    anchor("base", base)
   } else {
     anchor("tip", vector.add(tip, vector.scale(dir, _calculate-tip-offset(style))))
+    anchor("base", vector.sub(base, vector.scale(dir, style.stroke.thickness / 2)))
   }
-  anchor("base", vector.sub(base, vector.scale(dir, style.stroke.thickness / 2)))
 }
 
 #let create-diamond-tip-and-base-anchor(style, tip, base, center: none, ratio: 50%) = {

src/mark.typ

@@ -114,6 +114,12 @@
   let base = mark.base
   let origin = mark.at(style.anchor)
 
+  // Mirror anchors on mark center
+  if reverse {
+    (tip, base) = (base, tip)
+    origin = vector.sub(mark.center, vector.sub(origin, mark.center))
+  }
+
   mark.offset = vector.dist(origin, tip)
 
   let t = (
@@ -122,16 +128,17 @@
     matrix.transform-rotate-dir(dir, up),
     matrix.transform-rotate-z(-90deg),
 
-    // Apply mark transformations
-    if reverse {
-      matrix.transform-translate(-mark.length, 0, 0)
-    },
-    if slant not in (none, 0%) {
-      if type(slant) == ratio {
-        slant /= 100%
-      }
-      matrix.transform-shear-x(slant)
-    },
+    // Rotate mark to have base->tip on the x-axis
+    matrix.transform-rotate-z(if reverse {
+      vector.angle2(tip, base)
+    } else {
+      vector.angle2(base, tip)
+    }),
+
+    // Translate mark to have its anchor (tip, base, center) at (0,0)
+    matrix.transform-translate(..vector.scale(origin, if reverse {1} else {-1})),
+
+    // Mirror on x and/or y axis
     if flip or reverse {
       matrix.transform-scale({
         if flip {
@@ -143,11 +150,13 @@
       })
     },
 
-    /* Rotate mark to have base->tip on the x-axis */
-    matrix.transform-rotate-z(vector.angle2(base, tip)),
-
-    /* Translate mark to have its anchor (tip, base, center) at (0,0) */
-    matrix.transform-translate(..vector.scale(origin, -1)),
+    // Slant on x axis
+    if slant not in (none, 0%) {
+      if type(slant) == ratio {
+        slant /= 100%
+      }
+      matrix.transform-shear-x(slant)
+    },
   )
 
   mark.drawables = drawable.apply-transform(

tests/mark/anchor/test.typ

@@ -49,3 +49,21 @@
   (symbol: "x"),
   (symbol: ">"),
 ))
+
+#test-case({
+  import draw: *
+
+  anchor("a", (-1,0))
+  anchor("b", (+1,0))
+
+  line("a", "b")
+  mark("a", "b", symbol: "<", fill: black, anchor: "center")
+  mark("b", "a", symbol: "<", fill: black, anchor: "center")
+
+  anchor("c", (-1,-1))
+  anchor("d", (+1,-1))
+
+  line("c", "d")
+  mark("c", "d", symbol: ">", fill: black, anchor: "center")
+  mark("d", "c", symbol: ">", fill: black, anchor: "center")
+})