Merge webxr repository (#35228)

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

16 files changed, 2415 insertions, 0 deletions

diff --git a/components/shared/webxr/Cargo.toml b/components/shared/webxr/Cargo.toml
new file mode 100644
index 00000000000..47caee00131
--- /dev/null
+++ b/components/shared/webxr/Cargo.toml
@@ -0,0 +1,28 @@
+[package]
+name = "webxr-api"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+edition = "2018"
+
+homepage = "https://github.com/servo/webxr"
+repository = "https://github.com/servo/webxr"
+keywords = ["ar", "headset", "openxr", "vr", "webxr"]
+license = "MPL-2.0"
+
+description = '''A safe Rust API that provides a way to interact with
+virtual reality and augmented reality devices and integration with OpenXR.
+The API is inspired by the WebXR Device API (https://www.w3.org/TR/webxr/)
+but adapted to Rust design patterns.'''
+
+[lib]
+path = "lib.rs"
+
+[features]
+ipc = ["serde", "ipc-channel", "euclid/serde"]
+
+[dependencies]
+euclid = "0.22"
+ipc-channel = { version = "0.19", optional = true }
+log = "0.4"
+serde = { version = "1.0", optional = true }
+time = { version = "0.1", optional = true }
diff --git a/components/shared/webxr/device.rs b/components/shared/webxr/device.rs
new file mode 100644
index 00000000000..65f34d8560b
--- /dev/null
+++ b/components/shared/webxr/device.rs
@@ -0,0 +1,114 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! Traits to be implemented by backends
+
+use crate::ContextId;
+use crate::EnvironmentBlendMode;
+use crate::Error;
+use crate::Event;
+use crate::Floor;
+use crate::Frame;
+use crate::HitTestId;
+use crate::HitTestSource;
+use crate::InputSource;
+use crate::LayerId;
+use crate::LayerInit;
+use crate::Native;
+use crate::Quitter;
+use crate::Sender;
+use crate::Session;
+use crate::SessionBuilder;
+use crate::SessionInit;
+use crate::SessionMode;
+use crate::Viewports;
+
+use euclid::{Point2D, RigidTransform3D};
+
+/// A trait for discovering XR devices
+pub trait DiscoveryAPI<GL>: 'static {
+    fn request_session(
+        &mut self,
+        mode: SessionMode,
+        init: &SessionInit,
+        xr: SessionBuilder<GL>,
+    ) -> Result<Session, Error>;
+    fn supports_session(&self, mode: SessionMode) -> bool;
+}
+
+/// A trait for using an XR device
+pub trait DeviceAPI: 'static {
+    /// Create a new layer
+    fn create_layer(&mut self, context_id: ContextId, init: LayerInit) -> Result<LayerId, Error>;
+
+    /// Destroy a layer
+    fn destroy_layer(&mut self, context_id: ContextId, layer_id: LayerId);
+
+    /// The transform from native coordinates to the floor.
+    fn floor_transform(&self) -> Option<RigidTransform3D<f32, Native, Floor>>;
+
+    fn viewports(&self) -> Viewports;
+
+    /// Begin an animation frame.
+    fn begin_animation_frame(&mut self, layers: &[(ContextId, LayerId)]) -> Option<Frame>;
+
+    /// End an animation frame, render the layer to the device, and block waiting for the next frame.
+    fn end_animation_frame(&mut self, layers: &[(ContextId, LayerId)]);
+
+    /// Inputs registered with the device on initialization. More may be added, which
+    /// should be communicated through a yet-undecided event mechanism
+    fn initial_inputs(&self) -> Vec<InputSource>;
+
+    /// Sets the event handling channel
+    fn set_event_dest(&mut self, dest: Sender<Event>);
+
+    /// Quit the session
+    fn quit(&mut self);
+
+    fn set_quitter(&mut self, quitter: Quitter);
+
+    fn update_clip_planes(&mut self, near: f32, far: f32);
+
+    fn environment_blend_mode(&self) -> EnvironmentBlendMode {
+        // for VR devices, override for AR
+        EnvironmentBlendMode::Opaque
+    }
+
+    fn granted_features(&self) -> &[String];
+
+    fn request_hit_test(&mut self, _source: HitTestSource) {
+        panic!("This device does not support requesting hit tests");
+    }
+
+    fn cancel_hit_test(&mut self, _id: HitTestId) {
+        panic!("This device does not support hit tests");
+    }
+
+    fn update_frame_rate(&mut self, rate: f32) -> f32 {
+        rate
+    }
+
+    fn supported_frame_rates(&self) -> Vec<f32> {
+        Vec::new()
+    }
+
+    fn reference_space_bounds(&self) -> Option<Vec<Point2D<f32, Floor>>> {
+        None
+    }
+}
+
+impl<GL: 'static> DiscoveryAPI<GL> for Box<dyn DiscoveryAPI<GL>> {
+    fn request_session(
+        &mut self,
+        mode: SessionMode,
+        init: &SessionInit,
+        xr: SessionBuilder<GL>,
+    ) -> Result<Session, Error> {
+        (&mut **self).request_session(mode, init, xr)
+    }
+
+    fn supports_session(&self, mode: SessionMode) -> bool {
+        (&**self).supports_session(mode)
+    }
+}
diff --git a/components/shared/webxr/error.rs b/components/shared/webxr/error.rs
new file mode 100644
index 00000000000..86822f6fb7a
--- /dev/null
+++ b/components/shared/webxr/error.rs
@@ -0,0 +1,21 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+#[cfg(feature = "ipc")]
+use serde::{Deserialize, Serialize};
+
+/// Errors that can be produced by XR.
+
+// TODO: this is currently incomplete!
+
+#[derive(Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Error {
+    NoMatchingDevice,
+    CommunicationError,
+    ThreadCreationError,
+    InlineSession,
+    UnsupportedFeature(String),
+    BackendSpecific(String),
+}
diff --git a/components/shared/webxr/events.rs b/components/shared/webxr/events.rs
new file mode 100644
index 00000000000..338913464ba
--- /dev/null
+++ b/components/shared/webxr/events.rs
@@ -0,0 +1,80 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use euclid::RigidTransform3D;
+
+use crate::ApiSpace;
+use crate::BaseSpace;
+use crate::Frame;
+use crate::InputFrame;
+use crate::InputId;
+use crate::InputSource;
+use crate::SelectEvent;
+use crate::SelectKind;
+use crate::Sender;
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum Event {
+    /// Input source connected
+    AddInput(InputSource),
+    /// Input source disconnected
+    RemoveInput(InputId),
+    /// Input updated (this is a disconnect+reconnect)
+    UpdateInput(InputId, InputSource),
+    /// Session ended by device
+    SessionEnd,
+    /// Session focused/blurred/etc
+    VisibilityChange(Visibility),
+    /// Selection started / ended
+    Select(InputId, SelectKind, SelectEvent, Frame),
+    /// Input from an input source has changed
+    InputChanged(InputId, InputFrame),
+    /// Reference space has changed
+    ReferenceSpaceChanged(BaseSpace, RigidTransform3D<f32, ApiSpace, ApiSpace>),
+}
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum Visibility {
+    /// Session fully displayed to user
+    Visible,
+    /// Session still visible, but is not the primary focus
+    VisibleBlurred,
+    /// Session not visible
+    Hidden,
+}
+
+/// Convenience structure for buffering up events
+/// when no event callback has been set
+pub enum EventBuffer {
+    Buffered(Vec<Event>),
+    Sink(Sender<Event>),
+}
+
+impl Default for EventBuffer {
+    fn default() -> Self {
+        EventBuffer::Buffered(vec![])
+    }
+}
+
+impl EventBuffer {
+    pub fn callback(&mut self, event: Event) {
+        match *self {
+            EventBuffer::Buffered(ref mut events) => events.push(event),
+            EventBuffer::Sink(ref dest) => {
+                let _ = dest.send(event);
+            }
+        }
+    }
+
+    pub fn upgrade(&mut self, dest: Sender<Event>) {
+        if let EventBuffer::Buffered(ref mut events) = *self {
+            for event in events.drain(..) {
+                let _ = dest.send(event);
+            }
+        }
+        *self = EventBuffer::Sink(dest)
+    }
+}
diff --git a/components/shared/webxr/frame.rs b/components/shared/webxr/frame.rs
new file mode 100644
index 00000000000..2589953ecba
--- /dev/null
+++ b/components/shared/webxr/frame.rs
@@ -0,0 +1,60 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::Floor;
+use crate::HitTestId;
+use crate::HitTestResult;
+use crate::InputFrame;
+use crate::Native;
+use crate::SubImages;
+use crate::Viewer;
+use crate::Viewports;
+use crate::Views;
+
+use euclid::RigidTransform3D;
+
+/// The per-frame data that is provided by the device.
+/// https://www.w3.org/TR/webxr/#xrframe
+// TODO: other fields?
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct Frame {
+    /// The pose information of the viewer
+    pub pose: Option<ViewerPose>,
+    /// Frame information for each connected input source
+    pub inputs: Vec<InputFrame>,
+
+    /// Events that occur with the frame.
+    pub events: Vec<FrameUpdateEvent>,
+
+    /// The subimages to render to
+    pub sub_images: Vec<SubImages>,
+
+    /// The hit test results for this frame, if any
+    pub hit_test_results: Vec<HitTestResult>,
+
+    /// The average point in time this XRFrame is expected to be displayed on the devices' display
+    pub predicted_display_time: f64,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum FrameUpdateEvent {
+    UpdateFloorTransform(Option<RigidTransform3D<f32, Native, Floor>>),
+    UpdateViewports(Viewports),
+    HitTestSourceAdded(HitTestId),
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct ViewerPose {
+    /// The transform from the viewer to native coordinates
+    ///
+    /// This is equivalent to the pose of the viewer in native coordinates.
+    /// This is the inverse of the view matrix.
+    pub transform: RigidTransform3D<f32, Viewer, Native>,
+
+    // The various views
+    pub views: Views,
+}
diff --git a/components/shared/webxr/hand.rs b/components/shared/webxr/hand.rs
new file mode 100644
index 00000000000..fa6e8fafe80
--- /dev/null
+++ b/components/shared/webxr/hand.rs
@@ -0,0 +1,122 @@
+use crate::Native;
+use euclid::RigidTransform3D;
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct HandSpace;
+
+#[derive(Clone, Debug, Default)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct Hand<J> {
+    pub wrist: Option<J>,
+    pub thumb_metacarpal: Option<J>,
+    pub thumb_phalanx_proximal: Option<J>,
+    pub thumb_phalanx_distal: Option<J>,
+    pub thumb_phalanx_tip: Option<J>,
+    pub index: Finger<J>,
+    pub middle: Finger<J>,
+    pub ring: Finger<J>,
+    pub little: Finger<J>,
+}
+
+#[derive(Clone, Debug, Default)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct Finger<J> {
+    pub metacarpal: Option<J>,
+    pub phalanx_proximal: Option<J>,
+    pub phalanx_intermediate: Option<J>,
+    pub phalanx_distal: Option<J>,
+    pub phalanx_tip: Option<J>,
+}
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct JointFrame {
+    pub pose: RigidTransform3D<f32, HandSpace, Native>,
+    pub radius: f32,
+}
+
+impl Default for JointFrame {
+    fn default() -> Self {
+        Self {
+            pose: RigidTransform3D::identity(),
+            radius: 0.,
+        }
+    }
+}
+
+impl<J> Hand<J> {
+    pub fn map<R>(&self, map: impl (Fn(&Option<J>, Joint) -> Option<R>) + Copy) -> Hand<R> {
+        Hand {
+            wrist: map(&self.wrist, Joint::Wrist),
+            thumb_metacarpal: map(&self.thumb_metacarpal, Joint::ThumbMetacarpal),
+            thumb_phalanx_proximal: map(&self.thumb_phalanx_proximal, Joint::ThumbPhalanxProximal),
+            thumb_phalanx_distal: map(&self.thumb_phalanx_distal, Joint::ThumbPhalanxDistal),
+            thumb_phalanx_tip: map(&self.thumb_phalanx_tip, Joint::ThumbPhalanxTip),
+            index: self.index.map(|f, j| map(f, Joint::Index(j))),
+            middle: self.middle.map(|f, j| map(f, Joint::Middle(j))),
+            ring: self.ring.map(|f, j| map(f, Joint::Ring(j))),
+            little: self.little.map(|f, j| map(f, Joint::Little(j))),
+        }
+    }
+
+    pub fn get(&self, joint: Joint) -> Option<&J> {
+        match joint {
+            Joint::Wrist => self.wrist.as_ref(),
+            Joint::ThumbMetacarpal => self.thumb_metacarpal.as_ref(),
+            Joint::ThumbPhalanxProximal => self.thumb_phalanx_proximal.as_ref(),
+            Joint::ThumbPhalanxDistal => self.thumb_phalanx_distal.as_ref(),
+            Joint::ThumbPhalanxTip => self.thumb_phalanx_tip.as_ref(),
+            Joint::Index(f) => self.index.get(f),
+            Joint::Middle(f) => self.middle.get(f),
+            Joint::Ring(f) => self.ring.get(f),
+            Joint::Little(f) => self.little.get(f),
+        }
+    }
+}
+
+impl<J> Finger<J> {
+    pub fn map<R>(&self, map: impl (Fn(&Option<J>, FingerJoint) -> Option<R>) + Copy) -> Finger<R> {
+        Finger {
+            metacarpal: map(&self.metacarpal, FingerJoint::Metacarpal),
+            phalanx_proximal: map(&self.phalanx_proximal, FingerJoint::PhalanxProximal),
+            phalanx_intermediate: map(&self.phalanx_intermediate, FingerJoint::PhalanxIntermediate),
+            phalanx_distal: map(&self.phalanx_distal, FingerJoint::PhalanxDistal),
+            phalanx_tip: map(&self.phalanx_tip, FingerJoint::PhalanxTip),
+        }
+    }
+
+    pub fn get(&self, joint: FingerJoint) -> Option<&J> {
+        match joint {
+            FingerJoint::Metacarpal => self.metacarpal.as_ref(),
+            FingerJoint::PhalanxProximal => self.phalanx_proximal.as_ref(),
+            FingerJoint::PhalanxIntermediate => self.phalanx_intermediate.as_ref(),
+            FingerJoint::PhalanxDistal => self.phalanx_distal.as_ref(),
+            FingerJoint::PhalanxTip => self.phalanx_tip.as_ref(),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum FingerJoint {
+    Metacarpal,
+    PhalanxProximal,
+    PhalanxIntermediate,
+    PhalanxDistal,
+    PhalanxTip,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum Joint {
+    Wrist,
+    ThumbMetacarpal,
+    ThumbPhalanxProximal,
+    ThumbPhalanxDistal,
+    ThumbPhalanxTip,
+    Index(FingerJoint),
+    Middle(FingerJoint),
+    Ring(FingerJoint),
+    Little(FingerJoint),
+}
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
+    }
+}
diff --git a/components/shared/webxr/input.rs b/components/shared/webxr/input.rs
new file mode 100644
index 00000000000..9fcd2a18554
--- /dev/null
+++ b/components/shared/webxr/input.rs
@@ -0,0 +1,74 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::Hand;
+use crate::Input;
+use crate::JointFrame;
+use crate::Native;
+
+use euclid::RigidTransform3D;
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct InputId(pub u32);
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum Handedness {
+    None,
+    Left,
+    Right,
+}
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum TargetRayMode {
+    Gaze,
+    TrackedPointer,
+    Screen,
+    TransientPointer,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct InputSource {
+    pub handedness: Handedness,
+    pub target_ray_mode: TargetRayMode,
+    pub id: InputId,
+    pub supports_grip: bool,
+    pub hand_support: Option<Hand<()>>,
+    pub profiles: Vec<String>,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct InputFrame {
+    pub id: InputId,
+    pub target_ray_origin: Option<RigidTransform3D<f32, Input, Native>>,
+    pub grip_origin: Option<RigidTransform3D<f32, Input, Native>>,
+    pub pressed: bool,
+    pub hand: Option<Box<Hand<JointFrame>>>,
+    pub squeezed: bool,
+    pub button_values: Vec<f32>,
+    pub axis_values: Vec<f32>,
+    pub input_changed: bool,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum SelectEvent {
+    /// Selection started
+    Start,
+    /// Selection ended *without* it being a contiguous select event
+    End,
+    /// Selection ended *with* it being a contiguous select event
+    Select,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum SelectKind {
+    Select,
+    Squeeze,
+}
diff --git a/components/shared/webxr/layer.rs b/components/shared/webxr/layer.rs
new file mode 100644
index 00000000000..b0a607f290f
--- /dev/null
+++ b/components/shared/webxr/layer.rs
@@ -0,0 +1,296 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::Error;
+use crate::Viewport;
+use crate::Viewports;
+
+use euclid::Rect;
+use euclid::Size2D;
+
+use std::fmt::Debug;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering;
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(Deserialize, Serialize))]
+pub struct ContextId(pub u64);
+
+#[cfg(feature = "ipc")]
+use serde::{Deserialize, Serialize};
+
+pub trait GLTypes {
+    type Device;
+    type Context;
+    type Bindings;
+}
+
+pub trait GLContexts<GL: GLTypes> {
+    fn bindings(&mut self, device: &GL::Device, context_id: ContextId) -> Option<&GL::Bindings>;
+    fn context(&mut self, device: &GL::Device, context_id: ContextId) -> Option<&mut GL::Context>;
+}
+
+impl GLTypes for () {
+    type Bindings = ();
+    type Device = ();
+    type Context = ();
+}
+
+impl GLContexts<()> for () {
+    fn context(&mut self, _: &(), _: ContextId) -> Option<&mut ()> {
+        Some(self)
+    }
+
+    fn bindings(&mut self, _: &(), _: ContextId) -> Option<&()> {
+        Some(self)
+    }
+}
+
+pub trait LayerGrandManagerAPI<GL: GLTypes> {
+    fn create_layer_manager(&self, factory: LayerManagerFactory<GL>)
+        -> Result<LayerManager, Error>;
+
+    fn clone_layer_grand_manager(&self) -> LayerGrandManager<GL>;
+}
+
+pub struct LayerGrandManager<GL>(Box<dyn Send + LayerGrandManagerAPI<GL>>);
+
+impl<GL: GLTypes> Clone for LayerGrandManager<GL> {
+    fn clone(&self) -> Self {
+        self.0.clone_layer_grand_manager()
+    }
+}
+
+impl<GL> Debug for LayerGrandManager<GL> {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        "LayerGrandManager(...)".fmt(fmt)
+    }
+}
+
+impl<GL: GLTypes> LayerGrandManager<GL> {
+    pub fn new<GM>(grand_manager: GM) -> LayerGrandManager<GL>
+    where
+        GM: 'static + Send + LayerGrandManagerAPI<GL>,
+    {
+        LayerGrandManager(Box::new(grand_manager))
+    }
+
+    pub fn create_layer_manager<F, M>(&self, factory: F) -> Result<LayerManager, Error>
+    where
+        F: 'static + Send + FnOnce(&mut GL::Device, &mut dyn GLContexts<GL>) -> Result<M, Error>,
+        M: 'static + LayerManagerAPI<GL>,
+    {
+        self.0
+            .create_layer_manager(LayerManagerFactory::new(factory))
+    }
+}
+
+pub trait LayerManagerAPI<GL: GLTypes> {
+    fn create_layer(
+        &mut self,
+        device: &mut GL::Device,
+        contexts: &mut dyn GLContexts<GL>,
+        context_id: ContextId,
+        init: LayerInit,
+    ) -> Result<LayerId, Error>;
+
+    fn destroy_layer(
+        &mut self,
+        device: &mut GL::Device,
+        contexts: &mut dyn GLContexts<GL>,
+        context_id: ContextId,
+        layer_id: LayerId,
+    );
+
+    fn layers(&self) -> &[(ContextId, LayerId)];
+
+    fn begin_frame(
+        &mut self,
+        device: &mut GL::Device,
+        contexts: &mut dyn GLContexts<GL>,
+        layers: &[(ContextId, LayerId)],
+    ) -> Result<Vec<SubImages>, Error>;
+
+    fn end_frame(
+        &mut self,
+        device: &mut GL::Device,
+        contexts: &mut dyn GLContexts<GL>,
+        layers: &[(ContextId, LayerId)],
+    ) -> Result<(), Error>;
+}
+
+pub struct LayerManager(Box<dyn Send + LayerManagerAPI<()>>);
+
+impl Debug for LayerManager {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        "LayerManager(...)".fmt(fmt)
+    }
+}
+
+impl LayerManager {
+    pub fn create_layer(
+        &mut self,
+        context_id: ContextId,
+        init: LayerInit,
+    ) -> Result<LayerId, Error> {
+        self.0.create_layer(&mut (), &mut (), context_id, init)
+    }
+
+    pub fn destroy_layer(&mut self, context_id: ContextId, layer_id: LayerId) {
+        self.0.destroy_layer(&mut (), &mut (), context_id, layer_id);
+    }
+
+    pub fn begin_frame(
+        &mut self,
+        layers: &[(ContextId, LayerId)],
+    ) -> Result<Vec<SubImages>, Error> {
+        self.0.begin_frame(&mut (), &mut (), layers)
+    }
+
+    pub fn end_frame(&mut self, layers: &[(ContextId, LayerId)]) -> Result<(), Error> {
+        self.0.end_frame(&mut (), &mut (), layers)
+    }
+}
+
+impl LayerManager {
+    pub fn new<M>(manager: M) -> LayerManager
+    where
+        M: 'static + Send + LayerManagerAPI<()>,
+    {
+        LayerManager(Box::new(manager))
+    }
+}
+
+impl Drop for LayerManager {
+    fn drop(&mut self) {
+        log::debug!("Dropping LayerManager");
+        for (context_id, layer_id) in self.0.layers().to_vec() {
+            self.destroy_layer(context_id, layer_id);
+        }
+    }
+}
+
+pub struct LayerManagerFactory<GL: GLTypes>(
+    Box<
+        dyn Send
+            + FnOnce(
+                &mut GL::Device,
+                &mut dyn GLContexts<GL>,
+            ) -> Result<Box<dyn LayerManagerAPI<GL>>, Error>,
+    >,
+);
+
+impl<GL: GLTypes> Debug for LayerManagerFactory<GL> {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        "LayerManagerFactory(...)".fmt(fmt)
+    }
+}
+
+impl<GL: GLTypes> LayerManagerFactory<GL> {
+    pub fn new<F, M>(factory: F) -> LayerManagerFactory<GL>
+    where
+        F: 'static + Send + FnOnce(&mut GL::Device, &mut dyn GLContexts<GL>) -> Result<M, Error>,
+        M: 'static + LayerManagerAPI<GL>,
+    {
+        LayerManagerFactory(Box::new(move |device, contexts| {
+            Ok(Box::new(factory(device, contexts)?))
+        }))
+    }
+
+    pub fn build(
+        self,
+        device: &mut GL::Device,
+        contexts: &mut dyn GLContexts<GL>,
+    ) -> Result<Box<dyn LayerManagerAPI<GL>>, Error> {
+        (self.0)(device, contexts)
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(Deserialize, Serialize))]
+pub struct LayerId(usize);
+
+static NEXT_LAYER_ID: AtomicUsize = AtomicUsize::new(0);
+
+impl LayerId {
+    pub fn new() -> LayerId {
+        LayerId(NEXT_LAYER_ID.fetch_add(1, Ordering::SeqCst))
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Deserialize, Serialize))]
+pub enum LayerInit {
+    // https://www.w3.org/TR/webxr/#dictdef-xrwebgllayerinit
+    WebGLLayer {
+        antialias: bool,
+        depth: bool,
+        stencil: bool,
+        alpha: bool,
+        ignore_depth_values: bool,
+        framebuffer_scale_factor: f32,
+    },
+    // https://immersive-web.github.io/layers/#xrprojectionlayerinittype
+    ProjectionLayer {
+        depth: bool,
+        stencil: bool,
+        alpha: bool,
+        scale_factor: f32,
+    },
+    // TODO: other layer types
+}
+
+impl LayerInit {
+    pub fn texture_size(&self, viewports: &Viewports) -> Size2D<i32, Viewport> {
+        match self {
+            LayerInit::WebGLLayer {
+                framebuffer_scale_factor: scale,
+                ..
+            }
+            | LayerInit::ProjectionLayer {
+                scale_factor: scale,
+                ..
+            } => {
+                let native_size = viewports
+                    .viewports
+                    .iter()
+                    .fold(Rect::zero(), |acc, view| acc.union(view))
+                    .size;
+                (native_size.to_f32() * *scale).to_i32()
+            }
+        }
+    }
+}
+
+/// https://immersive-web.github.io/layers/#enumdef-xrlayerlayout
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Deserialize, Serialize))]
+pub enum LayerLayout {
+    // TODO: Default
+    // Allocates one texture
+    Mono,
+    // Allocates one texture, which is split in half vertically, giving two subimages
+    StereoLeftRight,
+    // Allocates one texture, which is split in half horizonally, giving two subimages
+    StereoTopBottom,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Deserialize, Serialize))]
+pub struct SubImages {
+    pub layer_id: LayerId,
+    pub sub_image: Option<SubImage>,
+    pub view_sub_images: Vec<SubImage>,
+}
+
+/// https://immersive-web.github.io/layers/#xrsubimagetype
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Deserialize, Serialize))]
+pub struct SubImage {
+    pub color_texture: u32,
+    // TODO: make this Option<NonZeroU32>
+    pub depth_stencil_texture: Option<u32>,
+    pub texture_array_index: Option<u32>,
+    pub viewport: Rect<i32, Viewport>,
+}
diff --git a/components/shared/webxr/lib.rs b/components/shared/webxr/lib.rs
new file mode 100644
index 00000000000..9acad34e0e5
--- /dev/null
+++ b/components/shared/webxr/lib.rs
@@ -0,0 +1,175 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! This crate defines the Rust API for WebXR. It is implemented by the `webxr` crate.
+
+mod device;
+mod error;
+mod events;
+mod frame;
+mod hand;
+mod hittest;
+mod input;
+mod layer;
+mod mock;
+mod registry;
+mod session;
+mod space;
+pub mod util;
+mod view;
+
+pub use device::DeviceAPI;
+pub use device::DiscoveryAPI;
+
+pub use error::Error;
+
+pub use events::Event;
+pub use events::EventBuffer;
+pub use events::Visibility;
+
+pub use frame::Frame;
+pub use frame::FrameUpdateEvent;
+pub use frame::ViewerPose;
+
+pub use hand::Finger;
+pub use hand::FingerJoint;
+pub use hand::Hand;
+pub use hand::HandSpace;
+pub use hand::Joint;
+pub use hand::JointFrame;
+
+pub use hittest::EntityType;
+pub use hittest::EntityTypes;
+pub use hittest::HitTestId;
+pub use hittest::HitTestResult;
+pub use hittest::HitTestSource;
+pub use hittest::HitTestSpace;
+pub use hittest::Ray;
+pub use hittest::Triangle;
+
+pub use input::Handedness;
+pub use input::InputFrame;
+pub use input::InputId;
+pub use input::InputSource;
+pub use input::SelectEvent;
+pub use input::SelectKind;
+pub use input::TargetRayMode;
+
+pub use layer::ContextId;
+pub use layer::GLContexts;
+pub use layer::GLTypes;
+pub use layer::LayerGrandManager;
+pub use layer::LayerGrandManagerAPI;
+pub use layer::LayerId;
+pub use layer::LayerInit;
+pub use layer::LayerLayout;
+pub use layer::LayerManager;
+pub use layer::LayerManagerAPI;
+pub use layer::LayerManagerFactory;
+pub use layer::SubImage;
+pub use layer::SubImages;
+
+pub use mock::MockButton;
+pub use mock::MockButtonType;
+pub use mock::MockDeviceInit;
+pub use mock::MockDeviceMsg;
+pub use mock::MockDiscoveryAPI;
+pub use mock::MockInputInit;
+pub use mock::MockInputMsg;
+pub use mock::MockRegion;
+pub use mock::MockViewInit;
+pub use mock::MockViewsInit;
+pub use mock::MockWorld;
+
+pub use registry::MainThreadRegistry;
+pub use registry::MainThreadWaker;
+pub use registry::Registry;
+
+pub use session::EnvironmentBlendMode;
+pub use session::MainThreadSession;
+pub use session::Quitter;
+pub use session::Session;
+pub use session::SessionBuilder;
+pub use session::SessionId;
+pub use session::SessionInit;
+pub use session::SessionMode;
+pub use session::SessionThread;
+
+pub use space::ApiSpace;
+pub use space::BaseSpace;
+pub use space::Space;
+
+pub use view::Capture;
+pub use view::CubeBack;
+pub use view::CubeBottom;
+pub use view::CubeLeft;
+pub use view::CubeRight;
+pub use view::CubeTop;
+pub use view::Display;
+pub use view::Floor;
+pub use view::Input;
+pub use view::LeftEye;
+pub use view::Native;
+pub use view::RightEye;
+pub use view::SomeEye;
+pub use view::View;
+pub use view::Viewer;
+pub use view::Viewport;
+pub use view::Viewports;
+pub use view::Views;
+pub use view::CUBE_BACK;
+pub use view::CUBE_BOTTOM;
+pub use view::CUBE_LEFT;
+pub use view::CUBE_RIGHT;
+pub use view::CUBE_TOP;
+pub use view::LEFT_EYE;
+pub use view::RIGHT_EYE;
+pub use view::VIEWER;
+
+#[cfg(feature = "ipc")]
+use std::thread;
+
+use std::time::Duration;
+
+#[cfg(feature = "ipc")]
+pub use ipc_channel::ipc::IpcSender as Sender;
+
+#[cfg(feature = "ipc")]
+pub use ipc_channel::ipc::IpcReceiver as Receiver;
+
+#[cfg(feature = "ipc")]
+pub use ipc_channel::ipc::channel;
+
+#[cfg(not(feature = "ipc"))]
+pub use std::sync::mpsc::{Receiver, RecvTimeoutError, Sender};
+
+#[cfg(not(feature = "ipc"))]
+pub fn channel<T>() -> Result<(Sender<T>, Receiver<T>), ()> {
+    Ok(std::sync::mpsc::channel())
+}
+
+#[cfg(not(feature = "ipc"))]
+pub fn recv_timeout<T>(receiver: &Receiver<T>, timeout: Duration) -> Result<T, RecvTimeoutError> {
+    receiver.recv_timeout(timeout)
+}
+
+#[cfg(feature = "ipc")]
+pub fn recv_timeout<T>(
+    receiver: &Receiver<T>,
+    timeout: Duration,
+) -> Result<T, ipc_channel::ipc::TryRecvError>
+where
+    T: serde::Serialize + for<'a> serde::Deserialize<'a>,
+{
+    // Sigh, polling, sigh.
+    let mut delay = timeout / 1000;
+    while delay < timeout {
+        if let Ok(msg) = receiver.try_recv() {
+            return Ok(msg);
+        }
+        thread::sleep(delay);
+        delay = delay * 2;
+    }
+    receiver.try_recv()
+}
diff --git a/components/shared/webxr/mock.rs b/components/shared/webxr/mock.rs
new file mode 100644
index 00000000000..91c15bae44b
--- /dev/null
+++ b/components/shared/webxr/mock.rs
@@ -0,0 +1,146 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::DiscoveryAPI;
+use crate::Display;
+use crate::EntityType;
+use crate::Error;
+use crate::Floor;
+use crate::Handedness;
+use crate::Input;
+use crate::InputId;
+use crate::InputSource;
+use crate::LeftEye;
+use crate::Native;
+use crate::Receiver;
+use crate::RightEye;
+use crate::SelectEvent;
+use crate::SelectKind;
+use crate::Sender;
+use crate::TargetRayMode;
+use crate::Triangle;
+use crate::Viewer;
+use crate::Viewport;
+use crate::Visibility;
+
+use euclid::{Point2D, Rect, RigidTransform3D, Transform3D};
+
+#[cfg(feature = "ipc")]
+use serde::{Deserialize, Serialize};
+
+/// A trait for discovering mock XR devices
+pub trait MockDiscoveryAPI<GL>: 'static {
+    fn simulate_device_connection(
+        &mut self,
+        init: MockDeviceInit,
+        receiver: Receiver<MockDeviceMsg>,
+    ) -> Result<Box<dyn DiscoveryAPI<GL>>, Error>;
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct MockDeviceInit {
+    pub floor_origin: Option<RigidTransform3D<f32, Floor, Native>>,
+    pub supports_inline: bool,
+    pub supports_vr: bool,
+    pub supports_ar: bool,
+    pub viewer_origin: Option<RigidTransform3D<f32, Viewer, Native>>,
+    pub views: MockViewsInit,
+    pub supported_features: Vec<String>,
+    pub world: Option<MockWorld>,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct MockViewInit<Eye> {
+    pub transform: RigidTransform3D<f32, Viewer, Eye>,
+    pub projection: Transform3D<f32, Eye, Display>,
+    pub viewport: Rect<i32, Viewport>,
+    /// field of view values, in radians
+    pub fov: Option<(f32, f32, f32, f32)>,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum MockViewsInit {
+    Mono(MockViewInit<Viewer>),
+    Stereo(MockViewInit<LeftEye>, MockViewInit<RightEye>),
+}
+
+#[derive(Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum MockDeviceMsg {
+    SetViewerOrigin(Option<RigidTransform3D<f32, Viewer, Native>>),
+    SetFloorOrigin(Option<RigidTransform3D<f32, Floor, Native>>),
+    SetViews(MockViewsInit),
+    AddInputSource(MockInputInit),
+    MessageInputSource(InputId, MockInputMsg),
+    VisibilityChange(Visibility),
+    SetWorld(MockWorld),
+    ClearWorld,
+    Disconnect(Sender<()>),
+    SetBoundsGeometry(Vec<Point2D<f32, Floor>>),
+    SimulateResetPose,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct MockInputInit {
+    pub source: InputSource,
+    pub pointer_origin: Option<RigidTransform3D<f32, Input, Native>>,
+    pub grip_origin: Option<RigidTransform3D<f32, Input, Native>>,
+    pub supported_buttons: Vec<MockButton>,
+}
+
+#[derive(Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum MockInputMsg {
+    SetHandedness(Handedness),
+    SetTargetRayMode(TargetRayMode),
+    SetProfiles(Vec<String>),
+    SetPointerOrigin(Option<RigidTransform3D<f32, Input, Native>>),
+    SetGripOrigin(Option<RigidTransform3D<f32, Input, Native>>),
+    /// Note: SelectEvent::Select here refers to a complete Select event,
+    /// not just the end event, i.e. it refers to
+    /// https://immersive-web.github.io/webxr-test-api/#dom-fakexrinputcontroller-simulateselect
+    TriggerSelect(SelectKind, SelectEvent),
+    Disconnect,
+    Reconnect,
+    SetSupportedButtons(Vec<MockButton>),
+    UpdateButtonState(MockButton),
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct MockRegion {
+    pub faces: Vec<Triangle>,
+    pub ty: EntityType,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct MockWorld {
+    pub regions: Vec<MockRegion>,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum MockButtonType {
+    Grip,
+    Touchpad,
+    Thumbstick,
+    OptionalButton,
+    OptionalThumbstick,
+}
+
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct MockButton {
+    pub button_type: MockButtonType,
+    pub pressed: bool,
+    pub touched: bool,
+    pub pressed_value: f32,
+    pub x_value: f32,
+    pub y_value: f32,
+}
diff --git a/components/shared/webxr/registry.rs b/components/shared/webxr/registry.rs
new file mode 100644
index 00000000000..337bb80a8a2
--- /dev/null
+++ b/components/shared/webxr/registry.rs
@@ -0,0 +1,262 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::DiscoveryAPI;
+use crate::Error;
+use crate::Frame;
+use crate::GLTypes;
+use crate::LayerGrandManager;
+use crate::MainThreadSession;
+use crate::MockDeviceInit;
+use crate::MockDeviceMsg;
+use crate::MockDiscoveryAPI;
+use crate::Receiver;
+use crate::Sender;
+use crate::Session;
+use crate::SessionBuilder;
+use crate::SessionId;
+use crate::SessionInit;
+use crate::SessionMode;
+
+use log::warn;
+
+#[cfg(feature = "ipc")]
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct Registry {
+    sender: Sender<RegistryMsg>,
+    waker: MainThreadWakerImpl,
+}
+
+pub struct MainThreadRegistry<GL> {
+    discoveries: Vec<Box<dyn DiscoveryAPI<GL>>>,
+    sessions: Vec<Box<dyn MainThreadSession>>,
+    mocks: Vec<Box<dyn MockDiscoveryAPI<GL>>>,
+    sender: Sender<RegistryMsg>,
+    receiver: Receiver<RegistryMsg>,
+    waker: MainThreadWakerImpl,
+    grand_manager: LayerGrandManager<GL>,
+    next_session_id: u32,
+}
+
+pub trait MainThreadWaker: 'static + Send {
+    fn clone_box(&self) -> Box<dyn MainThreadWaker>;
+    fn wake(&self);
+}
+
+impl Clone for Box<dyn MainThreadWaker> {
+    fn clone(&self) -> Self {
+        self.clone_box()
+    }
+}
+
+#[derive(Clone)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+struct MainThreadWakerImpl {
+    #[cfg(feature = "ipc")]
+    sender: Sender<()>,
+    #[cfg(not(feature = "ipc"))]
+    waker: Box<dyn MainThreadWaker>,
+}
+
+#[cfg(feature = "ipc")]
+impl MainThreadWakerImpl {
+    fn new(waker: Box<dyn MainThreadWaker>) -> Result<MainThreadWakerImpl, Error> {
+        let (sender, receiver) = crate::channel().or(Err(Error::CommunicationError))?;
+        ipc_channel::router::ROUTER.add_typed_route(receiver, Box::new(move |_| waker.wake()));
+        Ok(MainThreadWakerImpl { sender })
+    }
+
+    fn wake(&self) {
+        let _ = self.sender.send(());
+    }
+}
+
+#[cfg(not(feature = "ipc"))]
+impl MainThreadWakerImpl {
+    fn new(waker: Box<dyn MainThreadWaker>) -> Result<MainThreadWakerImpl, Error> {
+        Ok(MainThreadWakerImpl { waker })
+    }
+
+    pub fn wake(&self) {
+        self.waker.wake()
+    }
+}
+
+impl Registry {
+    pub fn supports_session(&mut self, mode: SessionMode, dest: Sender<Result<(), Error>>) {
+        let _ = self.sender.send(RegistryMsg::SupportsSession(mode, dest));
+        self.waker.wake();
+    }
+
+    pub fn request_session(
+        &mut self,
+        mode: SessionMode,
+        init: SessionInit,
+        dest: Sender<Result<Session, Error>>,
+        animation_frame_handler: Sender<Frame>,
+    ) {
+        let _ = self.sender.send(RegistryMsg::RequestSession(
+            mode,
+            init,
+            dest,
+            animation_frame_handler,
+        ));
+        self.waker.wake();
+    }
+
+    pub fn simulate_device_connection(
+        &mut self,
+        init: MockDeviceInit,
+        dest: Sender<Result<Sender<MockDeviceMsg>, Error>>,
+    ) {
+        let _ = self
+            .sender
+            .send(RegistryMsg::SimulateDeviceConnection(init, dest));
+        self.waker.wake();
+    }
+}
+
+impl<GL: 'static + GLTypes> MainThreadRegistry<GL> {
+    pub fn new(
+        waker: Box<dyn MainThreadWaker>,
+        grand_manager: LayerGrandManager<GL>,
+    ) -> Result<Self, Error> {
+        let (sender, receiver) = crate::channel().or(Err(Error::CommunicationError))?;
+        let discoveries = Vec::new();
+        let sessions = Vec::new();
+        let mocks = Vec::new();
+        let waker = MainThreadWakerImpl::new(waker)?;
+        Ok(MainThreadRegistry {
+            discoveries,
+            sessions,
+            mocks,
+            sender,
+            receiver,
+            waker,
+            grand_manager,
+            next_session_id: 0,
+        })
+    }
+
+    pub fn registry(&self) -> Registry {
+        Registry {
+            sender: self.sender.clone(),
+            waker: self.waker.clone(),
+        }
+    }
+
+    pub fn register<D>(&mut self, discovery: D)
+    where
+        D: DiscoveryAPI<GL>,
+    {
+        self.discoveries.push(Box::new(discovery));
+    }
+
+    pub fn register_mock<D>(&mut self, discovery: D)
+    where
+        D: MockDiscoveryAPI<GL>,
+    {
+        self.mocks.push(Box::new(discovery));
+    }
+
+    pub fn run_on_main_thread<S>(&mut self, session: S)
+    where
+        S: MainThreadSession,
+    {
+        self.sessions.push(Box::new(session));
+    }
+
+    pub fn run_one_frame(&mut self) {
+        while let Ok(msg) = self.receiver.try_recv() {
+            self.handle_msg(msg);
+        }
+        for session in &mut self.sessions {
+            session.run_one_frame();
+        }
+        self.sessions.retain(|session| session.running());
+    }
+
+    pub fn running(&self) -> bool {
+        self.sessions.iter().any(|session| session.running())
+    }
+
+    fn handle_msg(&mut self, msg: RegistryMsg) {
+        match msg {
+            RegistryMsg::SupportsSession(mode, dest) => {
+                let _ = dest.send(self.supports_session(mode));
+            }
+            RegistryMsg::RequestSession(mode, init, dest, raf_sender) => {
+                let _ = dest.send(self.request_session(mode, init, raf_sender));
+            }
+            RegistryMsg::SimulateDeviceConnection(init, dest) => {
+                let _ = dest.send(self.simulate_device_connection(init));
+            }
+        }
+    }
+
+    fn supports_session(&mut self, mode: SessionMode) -> Result<(), Error> {
+        for discovery in &self.discoveries {
+            if discovery.supports_session(mode) {
+                return Ok(());
+            }
+        }
+        Err(Error::NoMatchingDevice)
+    }
+
+    fn request_session(
+        &mut self,
+        mode: SessionMode,
+        init: SessionInit,
+        raf_sender: Sender<Frame>,
+    ) -> Result<Session, Error> {
+        for discovery in &mut self.discoveries {
+            if discovery.supports_session(mode) {
+                let raf_sender = raf_sender.clone();
+                let id = SessionId(self.next_session_id);
+                self.next_session_id += 1;
+                let xr = SessionBuilder::new(
+                    &mut self.sessions,
+                    raf_sender,
+                    self.grand_manager.clone(),
+                    id,
+                );
+                match discovery.request_session(mode, &init, xr) {
+                    Ok(session) => return Ok(session),
+                    Err(err) => warn!("XR device error {:?}", err),
+                }
+            }
+        }
+        warn!("no device could support the session");
+        Err(Error::NoMatchingDevice)
+    }
+
+    fn simulate_device_connection(
+        &mut self,
+        init: MockDeviceInit,
+    ) -> Result<Sender<MockDeviceMsg>, Error> {
+        for mock in &mut self.mocks {
+            let (sender, receiver) = crate::channel().or(Err(Error::CommunicationError))?;
+            if let Ok(discovery) = mock.simulate_device_connection(init.clone(), receiver) {
+                self.discoveries.insert(0, discovery);
+                return Ok(sender);
+            }
+        }
+        Err(Error::NoMatchingDevice)
+    }
+}
+
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+enum RegistryMsg {
+    RequestSession(
+        SessionMode,
+        SessionInit,
+        Sender<Result<Session, Error>>,
+        Sender<Frame>,
+    ),
+    SupportsSession(SessionMode, Sender<Result<(), Error>>),
+    SimulateDeviceConnection(MockDeviceInit, Sender<Result<Sender<MockDeviceMsg>, Error>>),
+}
diff --git a/components/shared/webxr/session.rs b/components/shared/webxr/session.rs
new file mode 100644
index 00000000000..be731b8c243
--- /dev/null
+++ b/components/shared/webxr/session.rs
@@ -0,0 +1,531 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::channel;
+use crate::ContextId;
+use crate::DeviceAPI;
+use crate::Error;
+use crate::Event;
+use crate::Floor;
+use crate::Frame;
+use crate::FrameUpdateEvent;
+use crate::HitTestId;
+use crate::HitTestSource;
+use crate::InputSource;
+use crate::LayerGrandManager;
+use crate::LayerId;
+use crate::LayerInit;
+use crate::Native;
+use crate::Receiver;
+use crate::Sender;
+use crate::Viewport;
+use crate::Viewports;
+
+use euclid::Point2D;
+use euclid::Rect;
+use euclid::RigidTransform3D;
+use euclid::Size2D;
+
+use log::warn;
+
+use std::thread;
+use std::time::Duration;
+
+#[cfg(feature = "ipc")]
+use serde::{Deserialize, Serialize};
+
+// How long to wait for an rAF.
+static TIMEOUT: Duration = Duration::from_millis(5);
+
+/// https://www.w3.org/TR/webxr/#xrsessionmode-enum
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum SessionMode {
+    Inline,
+    ImmersiveVR,
+    ImmersiveAR,
+}
+
+/// https://immersive-web.github.io/webxr/#dictdef-xrsessioninit
+#[derive(Clone, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct SessionInit {
+    pub required_features: Vec<String>,
+    pub optional_features: Vec<String>,
+    /// Secondary views are enabled with the `secondary-view` feature
+    /// but for performance reasons we also ask users to enable this pref
+    /// for now.
+    pub first_person_observer_view: bool,
+}
+
+impl SessionInit {
+    /// Helper function for validating a list of requested features against
+    /// a list of supported features for a given mode
+    pub fn validate(&self, mode: SessionMode, supported: &[String]) -> Result<Vec<String>, Error> {
+        for f in &self.required_features {
+            // viewer and local in immersive are granted by default
+            // https://immersive-web.github.io/webxr/#default-features
+            if f == "viewer" || (f == "local" && mode != SessionMode::Inline) {
+                continue;
+            }
+
+            if !supported.contains(f) {
+                return Err(Error::UnsupportedFeature(f.into()));
+            }
+        }
+        let mut granted = self.required_features.clone();
+        for f in &self.optional_features {
+            if f == "viewer"
+                || (f == "local" && mode != SessionMode::Inline)
+                || supported.contains(f)
+            {
+                granted.push(f.clone());
+            }
+        }
+
+        Ok(granted)
+    }
+
+    pub fn feature_requested(&self, f: &str) -> bool {
+        self.required_features
+            .iter()
+            .chain(self.optional_features.iter())
+            .find(|x| *x == f)
+            .is_some()
+    }
+}
+
+/// https://immersive-web.github.io/webxr-ar-module/#xrenvironmentblendmode-enum
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum EnvironmentBlendMode {
+    Opaque,
+    AlphaBlend,
+    Additive,
+}
+
+// The messages that are sent from the content thread to the session thread.
+#[derive(Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+enum SessionMsg {
+    CreateLayer(ContextId, LayerInit, Sender<Result<LayerId, Error>>),
+    DestroyLayer(ContextId, LayerId),
+    SetLayers(Vec<(ContextId, LayerId)>),
+    SetEventDest(Sender<Event>),
+    UpdateClipPlanes(/* near */ f32, /* far */ f32),
+    StartRenderLoop,
+    RenderAnimationFrame,
+    RequestHitTest(HitTestSource),
+    CancelHitTest(HitTestId),
+    UpdateFrameRate(f32, Sender<f32>),
+    Quit,
+    GetBoundsGeometry(Sender<Option<Vec<Point2D<f32, Floor>>>>),
+}
+
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+#[derive(Clone)]
+pub struct Quitter {
+    sender: Sender<SessionMsg>,
+}
+
+impl Quitter {
+    pub fn quit(&self) {
+        let _ = self.sender.send(SessionMsg::Quit);
+    }
+}
+
+/// An object that represents an XR session.
+/// This is owned by the content thread.
+/// https://www.w3.org/TR/webxr/#xrsession-interface
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct Session {
+    floor_transform: Option<RigidTransform3D<f32, Native, Floor>>,
+    viewports: Viewports,
+    sender: Sender<SessionMsg>,
+    environment_blend_mode: EnvironmentBlendMode,
+    initial_inputs: Vec<InputSource>,
+    granted_features: Vec<String>,
+    id: SessionId,
+    supported_frame_rates: Vec<f32>,
+}
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(Deserialize, Serialize))]
+pub struct SessionId(pub(crate) u32);
+
+impl Session {
+    pub fn id(&self) -> SessionId {
+        self.id
+    }
+
+    pub fn floor_transform(&self) -> Option<RigidTransform3D<f32, Native, Floor>> {
+        self.floor_transform.clone()
+    }
+
+    pub fn reference_space_bounds(&self) -> Option<Vec<Point2D<f32, Floor>>> {
+        let (sender, receiver) = channel().ok()?;
+        let _ = self.sender.send(SessionMsg::GetBoundsGeometry(sender));
+        receiver.recv().ok()?
+    }
+
+    pub fn initial_inputs(&self) -> &[InputSource] {
+        &self.initial_inputs
+    }
+
+    pub fn environment_blend_mode(&self) -> EnvironmentBlendMode {
+        self.environment_blend_mode
+    }
+
+    pub fn viewports(&self) -> &[Rect<i32, Viewport>] {
+        &self.viewports.viewports
+    }
+
+    /// A resolution large enough to contain all the viewports.
+    /// https://immersive-web.github.io/webxr/#recommended-webgl-framebuffer-resolution
+    ///
+    /// Returns None if the session is inline
+    pub fn recommended_framebuffer_resolution(&self) -> Option<Size2D<i32, Viewport>> {
+        self.viewports()
+            .iter()
+            .fold(None::<Rect<_, _>>, |acc, vp| {
+                Some(acc.map(|a| a.union(vp)).unwrap_or(*vp))
+            })
+            .map(|rect| Size2D::new(rect.max_x(), rect.max_y()))
+    }
+
+    pub fn create_layer(&self, context_id: ContextId, init: LayerInit) -> Result<LayerId, Error> {
+        let (sender, receiver) = channel().map_err(|_| Error::CommunicationError)?;
+        let _ = self
+            .sender
+            .send(SessionMsg::CreateLayer(context_id, init, sender));
+        receiver.recv().map_err(|_| Error::CommunicationError)?
+    }
+
+    /// Destroy a layer
+    pub fn destroy_layer(&self, context_id: ContextId, layer_id: LayerId) {
+        let _ = self
+            .sender
+            .send(SessionMsg::DestroyLayer(context_id, layer_id));
+    }
+
+    pub fn set_layers(&self, layers: Vec<(ContextId, LayerId)>) {
+        let _ = self.sender.send(SessionMsg::SetLayers(layers));
+    }
+
+    pub fn start_render_loop(&mut self) {
+        let _ = self.sender.send(SessionMsg::StartRenderLoop);
+    }
+
+    pub fn update_clip_planes(&mut self, near: f32, far: f32) {
+        let _ = self.sender.send(SessionMsg::UpdateClipPlanes(near, far));
+    }
+
+    pub fn set_event_dest(&mut self, dest: Sender<Event>) {
+        let _ = self.sender.send(SessionMsg::SetEventDest(dest));
+    }
+
+    pub fn render_animation_frame(&mut self) {
+        let _ = self.sender.send(SessionMsg::RenderAnimationFrame);
+    }
+
+    pub fn end_session(&mut self) {
+        let _ = self.sender.send(SessionMsg::Quit);
+    }
+
+    pub fn apply_event(&mut self, event: FrameUpdateEvent) {
+        match event {
+            FrameUpdateEvent::UpdateFloorTransform(floor) => self.floor_transform = floor,
+            FrameUpdateEvent::UpdateViewports(vp) => self.viewports = vp,
+            FrameUpdateEvent::HitTestSourceAdded(_) => (),
+        }
+    }
+
+    pub fn granted_features(&self) -> &[String] {
+        &self.granted_features
+    }
+
+    pub fn request_hit_test(&self, source: HitTestSource) {
+        let _ = self.sender.send(SessionMsg::RequestHitTest(source));
+    }
+
+    pub fn cancel_hit_test(&self, id: HitTestId) {
+        let _ = self.sender.send(SessionMsg::CancelHitTest(id));
+    }
+
+    pub fn update_frame_rate(&mut self, rate: f32, sender: Sender<f32>) {
+        let _ = self.sender.send(SessionMsg::UpdateFrameRate(rate, sender));
+    }
+
+    pub fn supported_frame_rates(&self) -> &[f32] {
+        &self.supported_frame_rates
+    }
+}
+
+#[derive(PartialEq)]
+enum RenderState {
+    NotInRenderLoop,
+    InRenderLoop,
+    PendingQuit,
+}
+
+/// For devices that want to do their own thread management, the `SessionThread` type is exposed.
+pub struct SessionThread<Device> {
+    receiver: Receiver<SessionMsg>,
+    sender: Sender<SessionMsg>,
+    layers: Vec<(ContextId, LayerId)>,
+    pending_layers: Option<Vec<(ContextId, LayerId)>>,
+    frame_count: u64,
+    frame_sender: Sender<Frame>,
+    running: bool,
+    device: Device,
+    id: SessionId,
+    render_state: RenderState,
+}
+
+impl<Device> SessionThread<Device>
+where
+    Device: DeviceAPI,
+{
+    pub fn new(
+        mut device: Device,
+        frame_sender: Sender<Frame>,
+        id: SessionId,
+    ) -> Result<Self, Error> {
+        let (sender, receiver) = crate::channel().or(Err(Error::CommunicationError))?;
+        device.set_quitter(Quitter {
+            sender: sender.clone(),
+        });
+        let frame_count = 0;
+        let running = true;
+        let layers = Vec::new();
+        let pending_layers = None;
+        Ok(SessionThread {
+            sender,
+            receiver,
+            device,
+            layers,
+            pending_layers,
+            frame_count,
+            frame_sender,
+            running,
+            id,
+            render_state: RenderState::NotInRenderLoop,
+        })
+    }
+
+    pub fn new_session(&mut self) -> Session {
+        let floor_transform = self.device.floor_transform();
+        let viewports = self.device.viewports();
+        let sender = self.sender.clone();
+        let initial_inputs = self.device.initial_inputs();
+        let environment_blend_mode = self.device.environment_blend_mode();
+        let granted_features = self.device.granted_features().into();
+        let supported_frame_rates = self.device.supported_frame_rates();
+        Session {
+            floor_transform,
+            viewports,
+            sender,
+            initial_inputs,
+            environment_blend_mode,
+            granted_features,
+            id: self.id,
+            supported_frame_rates,
+        }
+    }
+
+    pub fn run(&mut self) {
+        loop {
+            if let Ok(msg) = self.receiver.recv() {
+                if !self.handle_msg(msg) {
+                    self.running = false;
+                    break;
+                }
+            } else {
+                break;
+            }
+        }
+    }
+
+    fn handle_msg(&mut self, msg: SessionMsg) -> bool {
+        log::debug!("processing {:?}", msg);
+        match msg {
+            SessionMsg::SetEventDest(dest) => {
+                self.device.set_event_dest(dest);
+            }
+            SessionMsg::RequestHitTest(source) => {
+                self.device.request_hit_test(source);
+            }
+            SessionMsg::CancelHitTest(id) => {
+                self.device.cancel_hit_test(id);
+            }
+            SessionMsg::CreateLayer(context_id, layer_init, sender) => {
+                let result = self.device.create_layer(context_id, layer_init);
+                let _ = sender.send(result);
+            }
+            SessionMsg::DestroyLayer(context_id, layer_id) => {
+                self.layers.retain(|&(_, other_id)| layer_id != other_id);
+                self.device.destroy_layer(context_id, layer_id);
+            }
+            SessionMsg::SetLayers(layers) => {
+                self.pending_layers = Some(layers);
+            }
+            SessionMsg::StartRenderLoop => {
+                if let Some(layers) = self.pending_layers.take() {
+                    self.layers = layers;
+                }
+                let frame = match self.device.begin_animation_frame(&self.layers[..]) {
+                    Some(frame) => frame,
+                    None => {
+                        warn!("Device stopped providing frames, exiting");
+                        return false;
+                    }
+                };
+                self.render_state = RenderState::InRenderLoop;
+                let _ = self.frame_sender.send(frame);
+            }
+            SessionMsg::UpdateClipPlanes(near, far) => self.device.update_clip_planes(near, far),
+            SessionMsg::RenderAnimationFrame => {
+                self.frame_count += 1;
+
+                self.device.end_animation_frame(&self.layers[..]);
+
+                if self.render_state == RenderState::PendingQuit {
+                    self.quit();
+                    return false;
+                }
+
+                if let Some(layers) = self.pending_layers.take() {
+                    self.layers = layers;
+                }
+                #[allow(unused_mut)]
+                let mut frame = match self.device.begin_animation_frame(&self.layers[..]) {
+                    Some(frame) => frame,
+                    None => {
+                        warn!("Device stopped providing frames, exiting");
+                        return false;
+                    }
+                };
+
+                let _ = self.frame_sender.send(frame);
+            }
+            SessionMsg::UpdateFrameRate(rate, sender) => {
+                let new_framerate = self.device.update_frame_rate(rate);
+                let _ = sender.send(new_framerate);
+            }
+            SessionMsg::Quit => {
+                if self.render_state == RenderState::NotInRenderLoop {
+                    self.quit();
+                    return false;
+                } else {
+                    self.render_state = RenderState::PendingQuit;
+                }
+            }
+            SessionMsg::GetBoundsGeometry(sender) => {
+                let bounds = self.device.reference_space_bounds();
+                let _ = sender.send(bounds);
+            }
+        }
+        true
+    }
+
+    fn quit(&mut self) {
+        self.render_state = RenderState::NotInRenderLoop;
+        self.device.quit();
+    }
+}
+
+/// Devices that need to can run sessions on the main thread.
+pub trait MainThreadSession: 'static {
+    fn run_one_frame(&mut self);
+    fn running(&self) -> bool;
+}
+
+impl<Device> MainThreadSession for SessionThread<Device>
+where
+    Device: DeviceAPI,
+{
+    fn run_one_frame(&mut self) {
+        let frame_count = self.frame_count;
+        while frame_count == self.frame_count && self.running {
+            if let Ok(msg) = crate::recv_timeout(&self.receiver, TIMEOUT) {
+                self.running = self.handle_msg(msg);
+            } else {
+                break;
+            }
+        }
+    }
+
+    fn running(&self) -> bool {
+        self.running
+    }
+}
+
+/// A type for building XR sessions
+pub struct SessionBuilder<'a, GL> {
+    sessions: &'a mut Vec<Box<dyn MainThreadSession>>,
+    frame_sender: Sender<Frame>,
+    layer_grand_manager: LayerGrandManager<GL>,
+    id: SessionId,
+}
+
+impl<'a, GL: 'static> SessionBuilder<'a, GL> {
+    pub fn id(&self) -> SessionId {
+        self.id
+    }
+
+    pub(crate) fn new(
+        sessions: &'a mut Vec<Box<dyn MainThreadSession>>,
+        frame_sender: Sender<Frame>,
+        layer_grand_manager: LayerGrandManager<GL>,
+        id: SessionId,
+    ) -> Self {
+        SessionBuilder {
+            sessions,
+            frame_sender,
+            layer_grand_manager,
+            id,
+        }
+    }
+
+    /// For devices which are happy to hand over thread management to webxr.
+    pub fn spawn<Device, Factory>(self, factory: Factory) -> Result<Session, Error>
+    where
+        Factory: 'static + FnOnce(LayerGrandManager<GL>) -> Result<Device, Error> + Send,
+        Device: DeviceAPI,
+    {
+        let (acks, ackr) = crate::channel().or(Err(Error::CommunicationError))?;
+        let frame_sender = self.frame_sender;
+        let layer_grand_manager = self.layer_grand_manager;
+        let id = self.id;
+        thread::spawn(move || {
+            match factory(layer_grand_manager)
+                .and_then(|device| SessionThread::new(device, frame_sender, id))
+            {
+                Ok(mut thread) => {
+                    let session = thread.new_session();
+                    let _ = acks.send(Ok(session));
+                    thread.run();
+                }
+                Err(err) => {
+                    let _ = acks.send(Err(err));
+                }
+            }
+        });
+        ackr.recv().unwrap_or(Err(Error::CommunicationError))
+    }
+
+    /// For devices that need to run on the main thread.
+    pub fn run_on_main_thread<Device, Factory>(self, factory: Factory) -> Result<Session, Error>
+    where
+        Factory: 'static + FnOnce(LayerGrandManager<GL>) -> Result<Device, Error>,
+        Device: DeviceAPI,
+    {
+        let device = factory(self.layer_grand_manager)?;
+        let frame_sender = self.frame_sender;
+        let mut session_thread = SessionThread::new(device, frame_sender, self.id)?;
+        let session = session_thread.new_session();
+        self.sessions.push(Box::new(session_thread));
+        Ok(session)
+    }
+}
diff --git a/components/shared/webxr/space.rs b/components/shared/webxr/space.rs
new file mode 100644
index 00000000000..4ab116c5b90
--- /dev/null
+++ b/components/shared/webxr/space.rs
@@ -0,0 +1,28 @@
+use crate::InputId;
+use crate::Joint;
+use euclid::RigidTransform3D;
+
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+/// A stand-in type for "the space isn't statically known since
+/// it comes from client side code"
+pub struct ApiSpace;
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub enum BaseSpace {
+    Local,
+    Floor,
+    Viewer,
+    BoundedFloor,
+    TargetRay(InputId),
+    Grip(InputId),
+    Joint(InputId, Joint),
+}
+
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct Space {
+    pub base: BaseSpace,
+    pub offset: RigidTransform3D<f32, ApiSpace, ApiSpace>,
+}
diff --git a/components/shared/webxr/util.rs b/components/shared/webxr/util.rs
new file mode 100644
index 00000000000..e6342d42faf
--- /dev/null
+++ b/components/shared/webxr/util.rs
@@ -0,0 +1,129 @@
+use crate::FrameUpdateEvent;
+use crate::HitTestId;
+use crate::HitTestSource;
+use euclid::Transform3D;
+
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+pub struct ClipPlanes {
+    pub near: f32,
+    pub far: f32,
+    /// Was there an update that needs propagation to the client?
+    update: bool,
+}
+
+impl Default for ClipPlanes {
+    fn default() -> Self {
+        ClipPlanes {
+            near: 0.1,
+            far: 1000.,
+            update: false,
+        }
+    }
+}
+
+impl ClipPlanes {
+    pub fn update(&mut self, near: f32, far: f32) {
+        self.near = near;
+        self.far = far;
+        self.update = true;
+    }
+
+    /// Checks for and clears the pending update flag
+    pub fn recently_updated(&mut self) -> bool {
+        if self.update {
+            self.update = false;
+            true
+        } else {
+            false
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default)]
+#[cfg_attr(feature = "ipc", derive(serde::Serialize, serde::Deserialize))]
+/// Holds on to hit tests
+pub struct HitTestList {
+    tests: Vec<HitTestSource>,
+    uncommitted_tests: Vec<HitTestSource>,
+}
+
+impl HitTestList {
+    pub fn request_hit_test(&mut self, source: HitTestSource) {
+        self.uncommitted_tests.push(source)
+    }
+
+    pub fn commit_tests(&mut self) -> Vec<FrameUpdateEvent> {
+        let mut events = vec![];
+        for test in self.uncommitted_tests.drain(..) {
+            events.push(FrameUpdateEvent::HitTestSourceAdded(test.id));
+            self.tests.push(test);
+        }
+        events
+    }
+
+    pub fn tests(&self) -> &[HitTestSource] {
+        &self.tests
+    }
+
+    pub fn cancel_hit_test(&mut self, id: HitTestId) {
+        self.tests.retain(|s| s.id != id);
+        self.uncommitted_tests.retain(|s| s.id != id);
+    }
+}
+
+#[inline]
+/// Construct a projection matrix given the four angles from the center for the faces of the viewing frustum
+pub fn fov_to_projection_matrix<T, U>(
+    left: f32,
+    right: f32,
+    top: f32,
+    bottom: f32,
+    clip_planes: ClipPlanes,
+) -> Transform3D<f32, T, U> {
+    let near = clip_planes.near;
+    // XXXManishearth deal with infinite planes
+    let left = left.tan() * near;
+    let right = right.tan() * near;
+    let top = top.tan() * near;
+    let bottom = bottom.tan() * near;
+
+    frustum_to_projection_matrix(left, right, top, bottom, clip_planes)
+}
+
+#[inline]
+/// Construct matrix given the actual extent of the viewing frustum on the near plane
+pub fn frustum_to_projection_matrix<T, U>(
+    left: f32,
+    right: f32,
+    top: f32,
+    bottom: f32,
+    clip_planes: ClipPlanes,
+) -> Transform3D<f32, T, U> {
+    let near = clip_planes.near;
+    let far = clip_planes.far;
+
+    let w = right - left;
+    let h = top - bottom;
+    let d = far - near;
+
+    // Column-major order
+    Transform3D::new(
+        2. * near / w,
+        0.,
+        0.,
+        0.,
+        0.,
+        2. * near / h,
+        0.,
+        0.,
+        (right + left) / w,
+        (top + bottom) / h,
+        -(far + near) / d,
+        -1.,
+        0.,
+        0.,
+        -2. * far * near / d,
+        0.,
+    )
+}
diff --git a/components/shared/webxr/view.rs b/components/shared/webxr/view.rs
new file mode 100644
index 00000000000..566748f8a7a
--- /dev/null
+++ b/components/shared/webxr/view.rs
@@ -0,0 +1,170 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! This crate uses `euclid`'s typed units, and exposes different coordinate spaces.
+
+use euclid::Rect;
+use euclid::RigidTransform3D;
+use euclid::Transform3D;
+
+#[cfg(feature = "ipc")]
+use serde::{Deserialize, Serialize};
+
+use std::marker::PhantomData;
+
+/// The coordinate space of the viewer
+/// https://immersive-web.github.io/webxr/#dom-xrreferencespacetype-viewer
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Viewer {}
+
+/// The coordinate space of the floor
+/// https://immersive-web.github.io/webxr/#dom-xrreferencespacetype-local-floor
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Floor {}
+
+/// The coordinate space of the left eye
+/// https://immersive-web.github.io/webxr/#dom-xreye-left
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum LeftEye {}
+
+/// The coordinate space of the right eye
+/// https://immersive-web.github.io/webxr/#dom-xreye-right
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum RightEye {}
+
+/// The coordinate space of the left frustrum of a cubemap
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum CubeLeft {}
+
+/// The coordinate space of the right frustrum of a cubemap
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum CubeRight {}
+
+/// The coordinate space of the top frustrum of a cubemap
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum CubeTop {}
+
+/// The coordinate space of the bottom frustrum of a cubemap
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum CubeBottom {}
+
+/// The coordinate space of the back frustrum of a cubemap
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum CubeBack {}
+
+/// Pattern-match on eyes
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct SomeEye<Eye>(u8, PhantomData<Eye>);
+pub const LEFT_EYE: SomeEye<LeftEye> = SomeEye(0, PhantomData);
+pub const RIGHT_EYE: SomeEye<RightEye> = SomeEye(1, PhantomData);
+pub const VIEWER: SomeEye<Viewer> = SomeEye(2, PhantomData);
+pub const CUBE_LEFT: SomeEye<CubeLeft> = SomeEye(3, PhantomData);
+pub const CUBE_RIGHT: SomeEye<CubeRight> = SomeEye(4, PhantomData);
+pub const CUBE_TOP: SomeEye<CubeTop> = SomeEye(5, PhantomData);
+pub const CUBE_BOTTOM: SomeEye<CubeBottom> = SomeEye(6, PhantomData);
+pub const CUBE_BACK: SomeEye<CubeBack> = SomeEye(7, PhantomData);
+
+impl<Eye1, Eye2> PartialEq<SomeEye<Eye2>> for SomeEye<Eye1> {
+    fn eq(&self, rhs: &SomeEye<Eye2>) -> bool {
+        self.0 == rhs.0
+    }
+}
+
+/// The native 3D coordinate space of the device
+/// This is not part of the webvr specification.
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Native {}
+
+/// The normalized device coordinate space, where the display
+/// is from (-1,-1) to (1,1).
+// TODO: are we OK assuming that we can use the same coordinate system for all displays?
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Display {}
+
+/// The unnormalized device coordinate space, where the display
+/// is from (0,0) to (w,h), measured in pixels.
+// TODO: are we OK assuming that we can use the same coordinate system for all displays?
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Viewport {}
+
+/// The coordinate space of an input device
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Input {}
+
+/// The coordinate space of a secondary capture view
+#[derive(Clone, Copy, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Capture {}
+
+/// For each eye, the pose of that eye,
+/// its projection onto its display.
+/// For stereo displays, we have a `View<LeftEye>` and a `View<RightEye>`.
+/// For mono displays, we hagve a `View<Viewer>`
+/// https://immersive-web.github.io/webxr/#xrview
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct View<Eye> {
+    pub transform: RigidTransform3D<f32, Eye, Native>,
+    pub projection: Transform3D<f32, Eye, Display>,
+}
+
+impl<Eye> Default for View<Eye> {
+    fn default() -> Self {
+        View {
+            transform: RigidTransform3D::identity(),
+            projection: Transform3D::identity(),
+        }
+    }
+}
+
+impl<Eye> View<Eye> {
+    pub fn cast_unit<NewEye>(&self) -> View<NewEye> {
+        View {
+            transform: self.transform.cast_unit(),
+            projection: Transform3D::from_untyped(&self.projection.to_untyped()),
+        }
+    }
+}
+
+/// Whether a device is mono or stereo, and the views it supports.
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub enum Views {
+    /// Mono view for inline VR, viewport and projection matrices are calculated by client
+    Inline,
+    Mono(View<Viewer>),
+    Stereo(View<LeftEye>, View<RightEye>),
+    StereoCapture(View<LeftEye>, View<RightEye>, View<Capture>),
+    Cubemap(
+        View<Viewer>,
+        View<CubeLeft>,
+        View<CubeRight>,
+        View<CubeTop>,
+        View<CubeBottom>,
+        View<CubeBack>,
+    ),
+}
+
+/// A list of viewports per-eye in the order of fields in Views.
+///
+/// Not all must be in active use.
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "ipc", derive(Serialize, Deserialize))]
+pub struct Viewports {
+    pub viewports: Vec<Rect<i32, Viewport>>,
+}