bodies: Add a prism function

manual.typ

@@ -311,6 +311,10 @@ $ M_"world" = M_"world" dot M_"local" $
 
 #doc-style.parse-show-module("/src/draw/projection.typ")
 
+== Bodies
+
+#doc-style.parse-show-module("/src/draw/bodies.typ")
+
 = Coordinate Systems <coordinate-systems>
 A _coordinate_ is a position on the canvas on which the picture is drawn. They take the form of dictionaries and the following sub-sections define the key value pairs for each system. Some systems have a more implicit form as an array of values and `CeTZ` attempts to infer the system based on the element types.
 

src/draw.typ

@@ -2,5 +2,6 @@
 #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/shapes.typ": circle, circle-through, arc, arc-through, mark, line, grid, content, rect, bezier, bezier-through, catmull, hobby, merge-path
+#import "draw/bodies.typ": prism
 #import "draw/projection.typ": ortho, on-xy, on-xz, on-yz
 #import "draw/util.typ": assert-version

src/draw/bodies.typ

@@ -0,0 +1,101 @@
+#import "/src/coordinate.typ"
+#import "/src/drawable.typ"
+#import "/src/styles.typ"
+#import "/src/path-util.typ"
+#import "/src/util.typ"
+#import "/src/vector.typ"
+#import "/src/matrix.typ"
+#import "/src/process.typ"
+#import "/src/polygon.typ"
+
+/// Draw a prism by extending a single element
+/// into a direction.
+///
+/// Curved shapes get sampled into linear ones.
+///
+/// = parameters
+///
+/// = Styling
+/// *Root:* `prism`
+/// == Keys
+///   #show-parameter-block("front-stroke", ("stroke", "none"), [Front-face stroke], default: auto)
+///   #show-parameter-block("front-fill",   ("fill", "none"),   [Front-face fill], default: auto)
+///   #show-parameter-block("back-stroke",  ("stroke", "none"), [Back-face stroke], default: auto)
+///   #show-parameter-block("back-fill",    ("fill", "none"),   [Back-face fill], default: auto)
+///   #show-parameter-block("side-stroke",  ("stroke", "none"), [Side stroke], default: auto)
+///   #show-parameter-block("side-fill",    ("fill", "none"),   [Side fill], default: auto)
+///
+/// ```example
+/// ortho({
+///   // Draw a cube with and edge length of 2
+///   prism({
+///     rect((-1, -1), (rel: (2, 2)))
+///   }, 2)
+/// })
+/// ```
+///
+/// - body (elements): A single element to use as front-face
+/// - dir (number,vector): Z-distance or direction vector to extend
+///   the front-face along
+/// - samples (int): Number of samples to use for sampling curves
+#let prism(body, dir, samples: 10, ..style) = {
+  assert.eq(style.pos(), (),
+    message: "Prism takes no positional arguments")
+
+  let style = style.named()
+  (ctx => {
+    let transform = ctx.transform
+    ctx.transform = matrix.ident()
+    let (ctx, drawables, bounds) = process.many(ctx, util.resolve-body(ctx, body))
+    ctx.transform = transform
+
+    assert.eq(drawables.len(), 1,
+      message: "Prism shape must be a single drawable.")
+
+    let points = polygon.from-segments(drawables.first().segments, samples: samples)
+
+    let style = styles.resolve(ctx.style, merge: style, root: "prism")
+
+    // Normal to extend the front face along
+    let n = if type(dir) == array {
+      dir.map(util.resolve-number.with(ctx))
+    } else {
+      (0, 0, util.resolve-number(ctx, dir))
+    }
+
+    let stroke = (:)
+    let fill = (:)
+    for face in ("front", "back", "side") {
+      stroke.insert(face, style.at("stroke-" + face, default: style.stroke))
+      fill.insert(face, style.at("fill-" + face, default: style.fill))
+    }
+
+    let drawables = ()
+    let back-points = util.apply-transform(matrix.transform-translate(..n), ..points)
+
+    // Back
+    let back = drawable.path(path-util.line-segment(back-points.rev()),
+      close: true, stroke: stroke.back, fill: fill.back)
+    drawables.push(back)
+
+    // Sides
+    for i in range(0, points.len()) {
+      let k = calc.rem(i + 1, points.len())
+
+      let quad = (points.at(i), back-points.at(i), back-points.at(k), points.at(k))
+      let side = drawable.path(path-util.line-segment(quad),
+        close: true, stroke: stroke.side, fill: fill.side)
+      drawables.push(side)
+    }
+
+    // Front
+    let front = drawable.path(path-util.line-segment(points),
+      close: true, stroke: stroke.front, fill: fill.front)
+    drawables.push(front)
+
+    return (
+      ctx: ctx,
+      drawables: drawable.apply-transform(ctx.transform, drawables),
+    )
+  },)
+}

src/styles.typ

@@ -129,6 +129,10 @@
     fill: auto,
     stroke: auto,
   ),
+  prism: (
+    stroke: auto,
+    fill: auto,
+  ),
 )
 
 /// You can use this to combine the style in `ctx`, the style given by a user for a single element and an element's default style. 

tests/bodies/test.typ

@@ -0,0 +1,62 @@
+#set page(width: auto, height: auto)
+#import "/src/lib.typ": *
+#import "/tests/helper.typ": *
+
+#let h-test-case = test-case
+#let test-case(body) = h-test-case({
+  draw.set-style(stroke: (join: "round"))
+  body
+})
+
+#test-case({
+  import draw: *
+  prism({ rect((-1, -1), (1, 1)) }, 1)
+})
+
+#test-case({
+  import draw: *
+  prism({
+    circle((0,0))
+  }, samples: 3, 1)
+})
+
+#test-case({
+  import draw: *
+  set-style(prism: (
+    fill-back: blue,
+    fill-front: red,
+    fill-side: yellow,
+  ))
+  ortho(cull-face: "cw", {
+    prism({
+      line((-1, -1), (1, -1), (0, 1), close: true)
+    }, -2)
+    translate((3, 0, 0))
+    rotate(y: 160deg)
+    prism({
+      line((-1, -1), (1, -1), (0, 0), close: true)
+    }, -2)
+  })
+})
+
+#test-case({
+  import draw: *
+  ortho(x: 10deg, y: 30deg, {
+    prism({
+      translate((1,0,0))
+      rect((-1, -1), (1, 1))
+    }, 2)
+    prism({
+      translate((-2,0,0))
+      rect((-1, -1), (1, 1))
+    }, 2)
+    prism({
+      translate((1,0,-3))
+      rect((-1, -1), (1, 1))
+    }, 2)
+    prism({
+      translate((-2,0,-3))
+      rect((-1, -1), (1, 1))
+    }, 2)
+  })
+})