2 files changed, 62 insertions, 0 deletions
diff --git a/third_party/rust/uniffi-example-geometry/src/geometry.udl b/third_party/rust/uniffi-example-geometry/src/geometry.udl
new file mode 100644
index 0000000000..af60d429bf
--- /dev/null
+++ b/third_party/rust/uniffi-example-geometry/src/geometry.udl
@@ -0,0 +1,15 @@
+
+namespace geometry {
+  double gradient(Line ln);
+  Point? intersection(Line ln1, Line ln2);
+};
+
+dictionary Point {
+  double coord_x;
+  double coord_y;
+};
+
+dictionary Line {
+  Point start;
+  Point end;
+};
diff --git a/third_party/rust/uniffi-example-geometry/src/lib.rs b/third_party/rust/uniffi-example-geometry/src/lib.rs
new file mode 100644
index 0000000000..0e6add54f2
--- /dev/null
+++ b/third_party/rust/uniffi-example-geometry/src/lib.rs
@@ -0,0 +1,47 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// https://rust-lang.github.io/rust-clippy/master/index.html#float_cmp
+// Silence, clippy!
+const EPSILON: f64 = 0.0001f64;
+
+#[derive(Debug, Clone)]
+pub struct Point {
+    coord_x: f64,
+    coord_y: f64,
+}
+
+#[derive(Debug, Clone)]
+pub struct Line {
+    start: Point,
+    end: Point,
+}
+
+pub fn gradient(ln: Line) -> f64 {
+    let rise = ln.end.coord_y - ln.start.coord_y;
+    let run = ln.end.coord_x - ln.start.coord_x;
+    rise / run
+}
+
+pub fn intersection(ln1: Line, ln2: Line) -> Option<Point> {
+    // TODO: yuck, should be able to take &Line as argument here
+    // and have rust figure it out with a bunch of annotations...
+    let g1 = gradient(ln1.clone());
+    let z1 = ln1.start.coord_y - g1 * ln1.start.coord_x;
+    let g2 = gradient(ln2.clone());
+    let z2 = ln2.start.coord_y - g2 * ln2.start.coord_x;
+    // Parallel lines do not intersect.
+    if (g1 - g2).abs() < EPSILON {
+        return None;
+    }
+    // Otherwise, they intersect at this fancy calculation that
+    // I found on wikipedia.
+    let x = (z2 - z1) / (g1 - g2);
+    Some(Point {
+        coord_x: x,
+        coord_y: g1 * x + z1,
+    })
+}
+
+include!(concat!(env!("OUT_DIR"), "/geometry.uniffi.rs"));