Refactor & Improve Marks (#610)

* mark: Refactor mark drawing

* mark: Add recursion guard + panic

* mark: Fix typo

* mark: Fixe reversed marks

* tests: Update

* mark: Fix mark filling

* tests: Update

* mark: Fix reversal + miter calculation

* mark: Support user marks

* mark: Fix user mnemonic

* tests: Add tests for custom marks

* Update docstring to new format

* Update changelog

* Minor fixes

* Docs add example

* Review stuff

CHANGES.md

@@ -22,6 +22,8 @@ package called `cetz-plot`.
 - Element names are now checked to not contain a "." character.
 - Fixed intersection bug for content with `anchor:` set.
 - **BREAKING** The winding order of _all_ elements has been changed to CCW.
+- You can now add custom marks via `register-mark`.
+- Mark anchor (tip, base, center) calcuation got fixed.
 
 ## Draw
 - Added `floating` function for drawing elements without affecting bounding boxes.

src/canvas.typ

@@ -53,6 +53,11 @@
     nodes: (:),
     // group stack
     groups: (),
+    // user defined marks
+    marks: (
+      mnemonics: (:),
+      marks: (:),
+    )
   )
 
   let (ctx, bounds, drawables) = process.many(ctx, body)

src/draw.typ

@@ -1,6 +1,6 @@
 #import "draw/grouping.typ": intersections, group, scope, anchor, copy-anchors, set-ctx, get-ctx, for-each-anchor, on-layer, hide, floating
 #import "draw/transformations.typ": set-transform, rotate, translate, scale, set-origin, move-to, set-viewport
-#import "draw/styling.typ": set-style, fill, stroke
+#import "draw/styling.typ": set-style, fill, stroke, register-mark
 #import "draw/shapes.typ": circle, circle-through, arc, arc-through, mark, line, grid, content, rect, bezier, bezier-through, catmull, hobby, merge-path
 #import "draw/projection.typ": ortho, on-xy, on-xz, on-yz
 #import "draw/util.typ": assert-version

src/draw/styling.typ

@@ -30,3 +30,40 @@
 ///
 /// - stroke (stroke): Stroke style
 #let stroke(stroke) = set-style(stroke: stroke)
+
+/// Register a custom mark to the canvas
+///
+/// The mark should contain both anchors called **tip** and **base** that are used to determine the marks orientation. If unset both default to `(0, 0)`.
+/// An anchor named **center** is used as center of the mark, if present. Otherwise the mid between **tip** and **base** is used.
+///
+/// ```typc example
+/// register-mark(":)", style => {
+///   circle((0,0), radius: .5, fill: yellow)
+///   arc((0,0), start: 180deg + 30deg, delta: 180deg - 60deg, anchor: "origin", radius: .3)
+///   circle((-0.15, 0.15), radius: .1, fill: white)
+///   circle((-0.10, 0.10), radius: .025, fill: black)
+///   circle(( 0.15, 0.15), radius: .1, fill: white)
+///   circle(( 0.20, 0.10), radius: .025, fill: black)
+///
+///   anchor("tip",  ( 0.5, 0))
+///   anchor("base", (-0.5, 0))
+/// })
+///
+/// line((0,0), (3,0), mark: (end: ":)"))
+/// ```
+///
+/// - symbol (str): Mark name
+/// - mnemonic (none,str): Mark short name
+/// - body (function): Mark drawing callback, receiving the mark style as argument and returning elements. Format `(styles) => elements`.
+#let register-mark(symbol, body, mnemonic: none) = {
+  assert(type(symbol) == str)
+  assert(type(body) == function)
+
+  (ctx => {
+    ctx.marks.marks.insert(symbol, body)
+    if type(mnemonic) == str and mnemonic.len() > 0 {
+      ctx.marks.mnemonics.insert(mnemonic, symbol)
+    }
+    return (ctx: ctx)
+  },)
+}