intersection: Provide sort functions

src/draw/grouping.typ

@@ -115,7 +115,13 @@
 /// - name (str): Name to prepend to the generated anchors. (Not to be confused with other `name` arguments that allow the use of anchor coordinates.)
 /// - ..elements (elements,str): Elements and/or element names to calculate intersections with. Elements referred to by name are (unlike elements passed) not drawn by the intersections function!
 /// - samples (int): Number of samples to use for non-linear path segments. A higher sample count can give more precise results but worse performance.
-#let intersections(name, ..elements, samples: 10) = {
+/// - sort (none,function): A function of the form `(context, array<vector>) -> array<vector>`
+///   that gets called with the list of intersection points.
+///
+///   CeTZ provides the following sorting functions:
+///     - sorting.points-by-distace(points, reference: (0, 0, 0))
+///     - sorting.points-by-angle(points, reference: (0, 0, 0))
+#let intersections(name, ..elements, samples: 10, sort: none) = {
   samples = calc.clamp(samples, 2, 2500)
 
   assert(type(name) == str and name != "",
@@ -169,6 +175,11 @@
         }
       }
     }
+
+    if sort != none {
+      pts = (sort)(ctx, pts)
+    }
+
     let anchors = (:)
     for (i, pt) in pts.enumerate() {
       anchors.insert(str(i), pt)

src/lib.typ

@@ -15,6 +15,7 @@
 #import "path-util.typ"
 #import "mark.typ"
 #import "mark-shapes.typ"
+#import "sorting.typ"
 
 // Libraries
 #import "lib/palette.typ"

src/sorting.typ

@@ -0,0 +1,29 @@
+#import "/src/vector.typ"
+#import "/src/util.typ"
+
+/// Sort list of points by distance to a
+/// reference point.
+///
+/// - points (array): List of points to sort
+/// - reference (vec): Reference point
+/// -> List of points
+#let points-by-distance(ctx, points, reference: (0, 0, 0)) = {
+  let reference = util.apply-transform(ctx.transform, reference)
+  return points.sorted(key: pt => {
+    vector.dist(pt, reference)
+  })
+}
+
+/// Sort list of 2D points by angle to a
+/// reference 2D point in CCW order.
+/// Z component is ignored.
+///
+/// - points (array): List of points to sort
+/// - reference (vec): Reference point
+/// -> List of points
+#let points-by-angle(ctx, points, reference: (0, 0, 0)) = {
+  let (rx, ry, ..) = util.apply-transform(ctx.transform, reference)
+  return points.sorted(key: ((px, py, ..)) => {
+    360deg - calc.atan2(rx - px, ry - py)
+  })
+}

tests/intersection/test.typ

@@ -1,5 +1,6 @@
 #set page(width: auto, height: auto)
 #import "/src/lib.typ": *
+#import "/tests/helper.typ": *
 
 #let test(body) = canvas(length: 1cm, {
   import draw: *
@@ -66,7 +67,7 @@
   })
 })
 
-#box(stroke: 2pt + red, canvas({
+#test-case({
   import draw: *
 
   intersections("i", {
@@ -76,9 +77,9 @@
     line("a.default", "b.default", stroke: none)
   })
   line("i.0", "i.1", mark: (end: ">"))
-}))
+})
 
-#box(stroke: 2pt + red, canvas({
+#test-case({
   import draw: *
 
   circle((0,0), name: "a")
@@ -89,4 +90,20 @@
   for-each-anchor("i", (name) => {
     circle("i."+name, radius: .1, fill: red)
   })
-}))
+})
+
+#test-case(fn => {
+  import draw: *
+
+  let c = circle((1,1), name: "a", radius: 1.25)
+  let r = rect((0,0), (2,2), name: "b")
+  intersections("i", r, c, sort: fn)
+
+  for-each-anchor("i", (name) => {
+    content((), [#name], frame: "circle", fill: white)
+  })
+}, args: (
+  none,
+  sorting.points-by-angle.with(reference: (1, 1)),
+  sorting.points-by-distance.with(reference: (0, 0.1)),
+))