angle: Add Right Angle Function (#415)

Adds a `right-angle` function to the angle library that behaves tikz
like.
Fixes #414.

src/lib/angle.typ

@@ -1,9 +1,9 @@
-#import "../drawable.typ"
-#import "../styles.typ"
-#import "../vector.typ"
-#import "../util.typ"
-#import "../coordinate.typ"
-#import "../anchor.typ" as anchor_
+#import "/src/drawable.typ"
+#import "/src/styles.typ"
+#import "/src/vector.typ"
+#import "/src/util.typ"
+#import "/src/coordinate.typ"
+#import "/src/anchor.typ" as anchor_
 #import "/src/draw.typ"
 
 // Angle default-style
@@ -63,7 +63,8 @@
   ..style
 ) = draw.group(name: name, ctx => {
   let style = styles.resolve(ctx.style, merge: style.named(), base: default-style, root: "angle")
-  let (ctx, origin, a, b) = coordinate.resolve(ctx, origin, a, b)
+  let (ctx, origin) = coordinate.resolve(ctx, origin)
+  let (ctx, a, b) = coordinate.resolve(ctx, a, b, update: false)
 
   assert(origin.at(2) == a.at(2) and a.at(2) == b.at(2),
     message: "Angle z coordinates of all three points must be equal")
@@ -132,3 +133,83 @@
     draw.content(label-pt, label)
   }
 })
+
+/// Draw a right angle between `a` and `b` through origin `origin`
+///
+/// #example(```
+/// line((0,0), (1,1.5), name: "a")
+/// line((0,0), (2,-1), name: "b")
+///
+/// // Draw an angle between the two lines
+/// cetz.angle.right-angle("a.start", "a.end", "b.end",
+///   radius: 1.5)
+/// ```)
+///
+/// *Style Root:* `angle`
+///
+/// *Style Keys:*
+///   #show-parameter-block("radius", ("number"), [
+///     The radius of the angles arc. If of type `ratio`, it is relative to the smaller distance of either origin to a or origin to b.], default: .5)
+///   #show-parameter-block("label-radius", ("number", "ratio"), [
+///     The radius of the angles label origin. If of type `ratio`, it is relative to the distance between `origin` and the angle corner.], default: 50%)
+///
+/// *Anchors*
+/// / `"a"`: Point a
+/// / `"b"`: Point b
+/// / `"origin"`: Origin
+/// / `"corner"`: Angle corner
+/// / `"label"`: Label center
+///
+/// - origin (coordinate): Angle origin
+/// - a (coordinate): Coordinate of side `a`, containing an angle between `origin` and `b`.
+/// - b (coordinate): Coordinate of side `b`, containing an angle between `origin` and `a`.
+/// - label (none,content): Draw a label at the angles "label" anchor.
+/// - name (none,string): Element name, used for querying anchors.
+/// - ..style (style): Style key-value pairs.
+#let right-angle(
+  origin,
+  a,
+  b,
+  label: "•",
+  name: none,
+  ..style
+) = draw.group(name: name, ctx => {
+  let style = styles.resolve(ctx.style, merge: style.named(), base: default-style, root: "angle")
+  let (ctx, origin) = coordinate.resolve(ctx, origin)
+  let (ctx, a, b) = coordinate.resolve(ctx, a, b, update: false)
+  let vo = origin; let va = a; let vb = b
+
+  // Radius can be relative to the min-distance between origin-a and origin-b
+  if type(style.radius) == ratio {
+    style.radius = style.radius * calc.min(vector.dist(vo, va), vector.dist(vo, vb)) / 100%
+  }
+  let (r, _) = util.resolve-radius(style.radius).map(util.resolve-number.with(ctx))
+
+  let va = vector.add(vo, vector.scale(vector.norm(vector.sub(va, vo)), r))
+  let vb = vector.add(vo, vector.scale(vector.norm(vector.sub(vb, vo)), r))
+  let angle-b = vector.angle2(vo, vb)
+  let vm = vector.add(va, (calc.cos(angle-b) * r, calc.sin(angle-b) * r, 0))
+
+  // Label radius can be relative to the distance between origin and the
+  // angle corner
+  if type(style.label-radius) == ratio {
+    style.label-radius = style.label-radius * vector.dist(vm, vo) / 100%
+  }
+  let (ra, _) = util.resolve-radius(style.label-radius).map(util.resolve-number.with(ctx))
+
+  if style.fill != none {
+    draw.line(vo, va, vm, vb, close: true, stroke: none, fill: style.fill)
+  }
+  draw.line(va, vm, vb, ..style, fill: none)
+
+  let label-pt = vector.scale(vector.norm(vector.sub(vm, vo)), ra)
+  if label != none {
+    draw.content(label-pt, label)
+  }
+
+  draw.anchor("a", a)
+  draw.anchor("b", b)
+  draw.anchor("origin", origin)
+  draw.anchor("corner", vm)
+  draw.anchor("label", label-pt)
+})

tests/angle/right-angle/test.typ

@@ -0,0 +1,64 @@
+#set page(width: auto, height: auto)
+#import "/src/lib.typ": *
+#import "/tests/helper.typ": *
+
+#test-case({
+  import draw: *
+  import angle: right-angle
+
+  for a in range(0, 360, step: 36) {
+    a *= 1deg
+    translate((1.5, 0, 0))
+    group({
+      let (o, a, b) = ((0,0), (calc.cos(a), calc.sin(a)), (calc.cos(a+90deg), calc.sin(a+90deg)))
+      line(a, o, b)
+      right-angle(o, a, b)
+    })
+  }
+})
+
+#test-case({
+  import draw: *
+  import angle: right-angle
+
+  for a in range(0, 360, step: 36) {
+    a *= 1deg
+    translate((1.5, 0, 0))
+    group({
+      let (o, a, b) = ((0,0), (calc.cos(a), calc.sin(a)), (calc.cos(a+45deg), calc.sin(a+45deg)))
+      line(a, o, b)
+      right-angle(o, a, b)
+    })
+  }
+})
+
+#test-case({
+  import draw: *
+  import angle: right-angle
+
+  for a in range(0, 360, step: 36) {
+    a *= 1deg
+    translate((1.5, 0, 0))
+    group({
+      let (o, a, b) = ((0,0), (calc.cos(a), calc.sin(a)), (calc.cos(a+120deg), calc.sin(a+120deg)))
+      line(a, o, b)
+      right-angle(o, a, b)
+    })
+  }
+})
+
+#test-case({
+  import draw: *
+  import angle: right-angle, angle
+
+  scale(3)
+  let (o, a, b) = ((0,0), (0,1), (1,0))
+  line(a, o, b)
+  right-angle(o, a, b, name: "angle")
+  for-each-anchor("angle", n => {
+    if n in ("a", "b", "origin", "corner", "label") {
+      circle("angle." + n, stroke: blue, radius: .1)
+      content("angle." + n, [#n])
+    }
+  })
+})