1 files changed, 179 insertions, 0 deletions
diff --git a/components/shared/webxr/hittest.rs b/components/shared/webxr/hittest.rs
new file mode 100644
index 00000000000..3e56ff8c357
--- /dev/null
+++ b/components/shared/webxr/hittest.rs
@@ -0,0 +1,179 @@
+use crate::ApiSpace;
+use crate::Native;
+use crate::Space;
+use euclid::Point3D;
+use euclid::RigidTransform3D;
+use euclid::Rotation3D;
+use euclid::Vector3D;
+use std::f32::EPSILON;
+use std::iter::FromIterator;
+
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+/// https://immersive-web.github.io/hit-test/#xrray
+pub struct Ray<Space> {
+    /// The origin of the ray
+    pub origin: Vector3D<f32, Space>,
+    /// The direction of the ray. Must be normalized.
+    pub direction: Vector3D<f32, Space>,
+}
+
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+/// https://immersive-web.github.io/hit-test/#enumdef-xrhittesttrackabletype
+pub enum EntityType {
+    Point,
+    Plane,
+    Mesh,
+}
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+/// https://immersive-web.github.io/hit-test/#dictdef-xrhittestoptionsinit
+pub struct HitTestSource {
+    pub id: HitTestId,
+    pub space: Space,
+    pub ray: Ray<ApiSpace>,
+    pub types: EntityTypes,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct HitTestId(pub u32);
+
+#[derive(Copy, Clone, Debug, Default)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+/// Vec<EntityType>, but better
+pub struct EntityTypes {
+    pub point: bool,
+    pub plane: bool,
+    pub mesh: bool,
+}
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct HitTestResult {
+    pub id: HitTestId,
+    pub space: RigidTransform3D<f32, HitTestSpace, Native>,
+}
+
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+/// The coordinate space of a hit test result
+pub struct HitTestSpace;
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct Triangle {
+    pub first: Point3D<f32, Native>,
+    pub second: Point3D<f32, Native>,
+    pub third: Point3D<f32, Native>,
+}
+
+impl EntityTypes {
+    pub fn is_type(self, ty: EntityType) -> bool {
+        match ty {
+            EntityType::Point => self.point,
+            EntityType::Plane => self.plane,
+            EntityType::Mesh => self.mesh,
+        }
+    }
+
+    pub fn add_type(&mut self, ty: EntityType) {
+        match ty {
+            EntityType::Point => self.point = true,
+            EntityType::Plane => self.plane = true,
+            EntityType::Mesh => self.mesh = true,
+        }
+    }
+}
+
+impl FromIterator<EntityType> for EntityTypes {
+    fn from_iter<T>(iter: T) -> Self
+    where
+        T: IntoIterator<Item = EntityType>,
+    {
+        iter.into_iter().fold(Default::default(), |mut acc, e| {
+            acc.add_type(e);
+            acc
+        })
+    }
+}
+
+impl Triangle {
+    /// https://en.wikipedia.org/wiki/M%C3%B6ller%E2%80%93Trumbore_intersection_algorithm
+    pub fn intersect(
+        self,
+        ray: Ray<Native>,
+    ) -> Option<RigidTransform3D<f32, HitTestSpace, Native>> {
+        let Triangle {
+            first: v0,
+            second: v1,
+            third: v2,
+        } = self;
+
+        let edge1 = v1 - v0;
+        let edge2 = v2 - v0;
+
+        let h = ray.direction.cross(edge2);
+        let a = edge1.dot(h);
+        if a > -EPSILON && a < EPSILON {
+            // ray is parallel to triangle
+            return None;
+        }
+
+        let f = 1. / a;
+
+        let s = ray.origin - v0.to_vector();
+
+        // barycentric coordinate of intersection point u
+        let u = f * s.dot(h);
+        // barycentric coordinates have range (0, 1)
+        if u < 0. || u > 1. {
+            // the intersection is outside the triangle
+            return None;
+        }
+
+        let q = s.cross(edge1);
+        // barycentric coordinate of intersection point v
+        let v = f * ray.direction.dot(q);
+
+        // barycentric coordinates have range (0, 1)
+        // and their sum must not be greater than 1
+        if v < 0. || u + v > 1. {
+            // the intersection is outside the triangle
+            return None;
+        }
+
+        let t = f * edge2.dot(q);
+
+        if t > EPSILON {
+            let origin = ray.origin + ray.direction * t;
+
+            // this is not part of the Möller-Trumbore algorithm, the hit test spec
+            // requires it has an orientation such that the Y axis points along
+            // the triangle normal
+            let normal = edge1.cross(edge2).normalize();
+            let y = Vector3D::new(0., 1., 0.);
+            let dot = normal.dot(y);
+            let rotation = if dot > -EPSILON && dot < EPSILON {
+                // vectors are parallel, return the vector itself
+                // XXXManishearth it's possible for the vectors to be
+                // antiparallel, unclear if normals need to be flipped
+                Rotation3D::identity()
+            } else {
+                let axis = normal.cross(y);
+                let cos = normal.dot(y);
+                // This is Rotation3D::around_axis(axis.normalize(), theta), however
+                // that is just Rotation3D::quaternion(axis.normalize().xyz * sin, cos),
+                // which is Rotation3D::quaternion(cross, dot)
+                Rotation3D::quaternion(axis.x, axis.y, axis.z, cos)
+            };
+
+            return Some(RigidTransform3D::new(rotation, origin));
+        }
+
+        // triangle is behind ray
+        None
+    }
+}