Auto merge of #23848 - asajeffrey:webxr-moar-channels, r=Manishearth

Replace use of callbacks in webxr by channels

<!-- Please describe your changes on the following line: -->

Use senders rather than callbacks in webxr.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because it's an internal change

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11 files changed, 109 insertions, 190 deletions

diff --git a/Cargo.lock b/Cargo.lock
index ebb2e03d7d1..8c691485ce5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -411,6 +411,7 @@ dependencies = [
  "webrender 0.60.0 (git+https://github.com/servo/webrender)",
  "webrender_api 0.60.0 (git+https://github.com/servo/webrender)",
  "webrender_traits 0.0.1",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
@@ -431,7 +432,7 @@ dependencies = [
  "typetag 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_api 0.60.0 (git+https://github.com/servo/webrender)",
  "webvr_traits 0.0.1",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
@@ -621,7 +622,7 @@ dependencies = [
  "webrender_api 0.60.0 (git+https://github.com/servo/webrender)",
  "webvr 0.0.1",
  "webvr_traits 0.0.1",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
@@ -664,7 +665,7 @@ dependencies = [
  "style_traits 0.0.1",
  "webrender_api 0.60.0 (git+https://github.com/servo/webrender)",
  "webvr_traits 0.0.1",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
@@ -1087,7 +1088,7 @@ dependencies = [
  "servo_url 0.0.1",
  "style_traits 0.0.1",
  "webrender_api 0.60.0 (git+https://github.com/servo/webrender)",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
@@ -2537,7 +2538,7 @@ dependencies = [
  "webrender_traits 0.0.1",
  "webvr 0.0.1",
  "webvr_traits 0.0.1",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
@@ -3912,7 +3913,7 @@ dependencies = [
  "uuid 0.7.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_api 0.60.0 (git+https://github.com/servo/webrender)",
  "webvr_traits 0.0.1",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
  "xml5ever 0.14.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -4004,7 +4005,7 @@ dependencies = [
  "url 1.7.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_api 0.60.0 (git+https://github.com/servo/webrender)",
  "webvr_traits 0.0.1",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
@@ -4101,8 +4102,8 @@ dependencies = [
  "servo-media 0.1.0 (git+https://github.com/servo/media)",
  "sig 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tinyfiledialogs 3.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "webxr 0.0.1 (git+https://github.com/servo/webxr)",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
  "winapi 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "winres 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "x11 2.17.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -5495,25 +5496,24 @@ dependencies = [
 [[package]]
 name = "webxr"
 version = "0.0.1"
-source = "git+https://github.com/servo/webxr#0418277175dbccf83e575c99d6b9c778bfdbe70b"
+source = "git+https://github.com/asajeffrey/webxr?branch=optional-glsync#da820a3ab266fce07c9a8abee3e6e9231cb93ec5"
 dependencies = [
  "euclid 0.20.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "gleam 0.6.18 (registry+https://github.com/rust-lang/crates.io-index)",
  "glutin 0.21.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "webxr-api 0.0.1 (git+https://github.com/servo/webxr)",
+ "webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)",
 ]
 
 [[package]]
 name = "webxr-api"
 version = "0.0.1"
-source = "git+https://github.com/servo/webxr#0418277175dbccf83e575c99d6b9c778bfdbe70b"
+source = "git+https://github.com/asajeffrey/webxr?branch=optional-glsync#da820a3ab266fce07c9a8abee3e6e9231cb93ec5"
 dependencies = [
  "euclid 0.20.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "gleam 0.6.18 (registry+https://github.com/rust-lang/crates.io-index)",
  "ipc-channel 0.11.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.88 (registry+https://github.com/rust-lang/crates.io-index)",
- "typetag 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -6142,8 +6142,8 @@ dependencies = [
 "checksum webrender 0.60.0 (git+https://github.com/servo/webrender)" = "<none>"
 "checksum webrender_api 0.60.0 (git+https://github.com/servo/webrender)" = "<none>"
 "checksum webrender_build 0.0.1 (git+https://github.com/servo/webrender)" = "<none>"
-"checksum webxr 0.0.1 (git+https://github.com/servo/webxr)" = "<none>"
-"checksum webxr-api 0.0.1 (git+https://github.com/servo/webxr)" = "<none>"
+"checksum webxr 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)" = "<none>"
+"checksum webxr-api 0.0.1 (git+https://github.com/asajeffrey/webxr?branch=optional-glsync)" = "<none>"
 "checksum weedle 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3bb43f70885151e629e2a19ce9e50bd730fd436cfd4b666894c9ce4de9141164"
 "checksum which 2.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b57acb10231b9493c8472b20cb57317d0679a49e0bdbee44b3b803a6473af164"
 "checksum winapi 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)" = "f10e386af2b13e47c89e7236a7a14a086791a2b88ebad6df9bf42040195cf770"
diff --git a/Cargo.toml b/Cargo.toml
index 060be41a5d2..b802517ea5e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -29,3 +29,7 @@ opt-level = 3
 mio = { git = "https://github.com/servo/mio.git", branch = "servo" }
 iovec = { git = "https://github.com/servo/iovec.git", branch = "servo" }
 cmake = { git = "https://github.com/alexcrichton/cmake-rs" }
+
+[patch."https://github.com/servo/webxr"]
+webxr = { git = "https://github.com/asajeffrey/webxr", branch = "optional-glsync" }
+webxr-api = { git = "https://github.com/asajeffrey/webxr", branch = "optional-glsync" }
diff --git a/components/canvas/Cargo.toml b/components/canvas/Cargo.toml
index 03a77826ac7..bdcb93b8507 100644
--- a/components/canvas/Cargo.toml
+++ b/components/canvas/Cargo.toml
@@ -37,3 +37,4 @@ servo_config = {path = "../config"}
 webrender = {git = "https://github.com/servo/webrender"}
 webrender_api = {git = "https://github.com/servo/webrender", features = ["ipc"]}
 webrender_traits = {path = "../webrender_traits"}
+webxr-api = {git = "https://github.com/servo/webxr", features = ["ipc"]}
diff --git a/components/canvas/webgl_mode/inprocess.rs b/components/canvas/webgl_mode/inprocess.rs
index 34a3f0eeb7a..1ca4e9c53cb 100644
--- a/components/canvas/webgl_mode/inprocess.rs
+++ b/components/canvas/webgl_mode/inprocess.rs
@@ -1,7 +1,6 @@
 /* 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::gl_context::GLContextFactory;
 use crate::webgl_thread::{WebGLMainThread, WebGLThread, WebGLThreadInit};
 use canvas_traits::webgl::webgl_channel;
@@ -17,6 +16,7 @@ use std::default::Default;
 use std::rc::Rc;
 use std::sync::{Arc, Mutex};
 use webrender_traits::{WebrenderExternalImageApi, WebrenderExternalImageRegistry};
+use webxr_api::WebGLExternalImageApi;
 
 /// WebGL Threading API entry point that lives in the constellation.
 pub struct WebGLThreads(WebGLSender<WebGLMsg>);
@@ -38,6 +38,7 @@ impl WebGLThreads {
     ) -> (
         WebGLThreads,
         Option<Rc<WebGLMainThread>>,
+        Box<dyn webxr_api::WebGLExternalImageApi>,
         Box<dyn WebrenderExternalImageApi>,
         Option<Box<dyn webrender::OutputImageHandler>>,
     ) {
@@ -77,6 +78,7 @@ impl WebGLThreads {
         (
             WebGLThreads(sender),
             webgl_thread,
+            external.sendable.clone_box(),
             Box::new(external),
             output_handler.map(|b| b as Box<_>),
         )
@@ -96,9 +98,8 @@ impl WebGLThreads {
     }
 }
 
-/// Bridge between the webrender::ExternalImage callbacks and the WebGLThreads.
-struct WebGLExternalImages {
-    webrender_gl: Rc<dyn gl::Gl>,
+/// Bridge between the webxr_api::ExternalImage callbacks and the WebGLThreads.
+struct SendableWebGLExternalImages {
     webgl_channel: WebGLSender<WebGLMsg>,
     // Used to avoid creating a new channel on each received WebRender request.
     lock_channel: (
@@ -107,24 +108,26 @@ struct WebGLExternalImages {
     ),
 }
 
-impl WebGLExternalImages {
-    fn new(webrender_gl: Rc<dyn gl::Gl>, channel: WebGLSender<WebGLMsg>) -> Self {
-        WebGLExternalImages {
-            webrender_gl,
+impl SendableWebGLExternalImages {
+    fn new(channel: WebGLSender<WebGLMsg>) -> Self {
+        Self {
             webgl_channel: channel,
             lock_channel: webgl_channel().unwrap(),
         }
     }
 }
 
-impl WebrenderExternalImageApi for WebGLExternalImages {
-    fn lock(&mut self, id: u64) -> (u32, Size2D<i32>) {
+impl webxr_api::WebGLExternalImageApi for SendableWebGLExternalImages {
+    fn lock(&self, id: usize) -> (u32, Size2D<i32>, Option<gl::GLsync>) {
         if let Some(main_thread) = WebGLMainThread::on_current_thread() {
             // If we're on the same thread as WebGL, we can get the data directly
-            main_thread
+            let (image_id, size) = main_thread
                 .thread_data
                 .borrow_mut()
-                .handle_lock_unsync(WebGLContextId(id as usize))
+                .handle_lock_unsync(WebGLContextId(id as usize));
+            // We don't need a GLsync object if we're running on the main thread
+            // Might be better to return an option?
+            (image_id, size, None)
         } else {
             // WebGL Thread has it's own GL command queue that we need to synchronize with the WR GL command queue.
             // The WebGLMsg::Lock message inserts a fence in the WebGL command queue.
@@ -135,16 +138,11 @@ impl WebrenderExternalImageApi for WebGLExternalImages {
                 ))
                 .unwrap();
             let (image_id, size, gl_sync) = self.lock_channel.1.recv().unwrap();
-            // The next glWaitSync call is run on the WR thread and it's used to synchronize the two
-            // flows of OpenGL commands in order to avoid WR using a semi-ready WebGL texture.
-            // glWaitSync doesn't block WR thread, it affects only internal OpenGL subsystem.
-            self.webrender_gl
-                .wait_sync(gl_sync as gl::GLsync, 0, gl::TIMEOUT_IGNORED);
-            (image_id, size)
+            (image_id, size, Some(gl_sync as gl::GLsync))
         }
     }
 
-    fn unlock(&mut self, id: u64) {
+    fn unlock(&self, id: usize) {
         if let Some(main_thread) = WebGLMainThread::on_current_thread() {
             // If we're on the same thread as WebGL, we can unlock directly
             main_thread
@@ -157,6 +155,42 @@ impl WebrenderExternalImageApi for WebGLExternalImages {
                 .unwrap()
         }
     }
+
+    fn clone_box(&self) -> Box<dyn webxr_api::WebGLExternalImageApi> {
+        Box::new(Self::new(self.webgl_channel.clone()))
+    }
+}
+
+/// Bridge between the webrender::ExternalImage callbacks and the WebGLThreads.
+struct WebGLExternalImages {
+    webrender_gl: Rc<dyn gl::Gl>,
+    sendable: SendableWebGLExternalImages,
+}
+
+impl WebGLExternalImages {
+    fn new(webrender_gl: Rc<dyn gl::Gl>, channel: WebGLSender<WebGLMsg>) -> Self {
+        Self {
+            webrender_gl,
+            sendable: SendableWebGLExternalImages::new(channel),
+        }
+    }
+}
+
+impl WebrenderExternalImageApi for WebGLExternalImages {
+    fn lock(&mut self, id: u64) -> (u32, Size2D<i32>) {
+        let (image_id, size, gl_sync) = self.sendable.lock(id as usize);
+        // The next glWaitSync call is run on the WR thread and it's used to synchronize the two
+        // flows of OpenGL commands in order to avoid WR using a semi-ready WebGL texture.
+        // glWaitSync doesn't block WR thread, it affects only internal OpenGL subsystem.
+        if let Some(gl_sync) = gl_sync {
+            self.webrender_gl.wait_sync(gl_sync, 0, gl::TIMEOUT_IGNORED);
+        }
+        (image_id, size)
+    }
+
+    fn unlock(&mut self, id: u64) {
+        self.sendable.unlock(id as usize);
+    }
 }
 
 /// struct used to implement DOMToTexture feature and webrender::OutputImageHandler trait.
diff --git a/components/canvas/webgl_thread.rs b/components/canvas/webgl_thread.rs
index 01262de02f2..f2099094127 100644
--- a/components/canvas/webgl_thread.rs
+++ b/components/canvas/webgl_thread.rs
@@ -10,7 +10,7 @@ use euclid::default::Size2D;
 use fnv::FnvHashMap;
 use gleam::gl;
 use half::f16;
-use ipc_channel::ipc::{self, IpcSender, OpaqueIpcMessage};
+use ipc_channel::ipc::{self, OpaqueIpcMessage};
 use ipc_channel::router::ROUTER;
 use offscreen_gl_context::{DrawBuffer, GLContext, NativeGLContextMethods};
 use pixels::{self, PixelFormat};
@@ -284,9 +284,6 @@ impl WebGLThread {
             WebGLMsg::Lock(ctx_id, sender) => {
                 self.handle_lock(ctx_id, sender);
             },
-            WebGLMsg::LockIPC(ctx_id, sender) => {
-                self.handle_lock_ipc(ctx_id, sender);
-            },
             WebGLMsg::Unlock(ctx_id) => {
                 self.handle_unlock(ctx_id);
             },
@@ -343,21 +340,6 @@ impl WebGLThread {
         context_id: WebGLContextId,
         sender: WebGLSender<(u32, Size2D<i32>, usize)>,
     ) {
-        sender.send(self.handle_lock_sync(context_id)).unwrap();
-    }
-
-    /// handle_lock, but unconditionally IPC (used by webxr)
-    fn handle_lock_ipc(
-        &mut self,
-        context_id: WebGLContextId,
-        sender: IpcSender<(u32, Size2D<i32>, usize)>,
-    ) {
-        sender.send(self.handle_lock_sync(context_id)).unwrap();
-    }
-
-    /// Shared code between handle_lock and handle_lock_ipc, does the actual syncing/flushing
-    /// but the caller must send the response back
-    fn handle_lock_sync(&mut self, context_id: WebGLContextId) -> (u32, Size2D<i32>, usize) {
         let data =
             Self::make_current_if_needed(context_id, &self.contexts, &mut self.bound_context_id)
                 .expect("WebGLContext not found in a WebGLMsg::Lock message");
@@ -374,7 +356,7 @@ impl WebGLThread {
         data.ctx.gl().flush();
         debug_assert!(data.ctx.gl().get_error() == gl::NO_ERROR);
 
-        (info.texture_id, info.size, gl_sync as usize)
+        let _ = sender.send((info.texture_id, info.size, gl_sync as usize));
     }
 
     /// A version of locking that doesn't return a GLsync object,
diff --git a/components/canvas_traits/webgl.rs b/components/canvas_traits/webgl.rs
index b33f5eae1be..a037b528874 100644
--- a/components/canvas_traits/webgl.rs
+++ b/components/canvas_traits/webgl.rs
@@ -4,10 +4,8 @@
 
 use euclid::default::{Rect, Size2D};
 use gleam::gl;
-use gleam::gl::GLsync;
-use gleam::gl::GLuint;
 use gleam::gl::Gl;
-use ipc_channel::ipc::{self, IpcBytesReceiver, IpcBytesSender, IpcSender, IpcSharedMemory};
+use ipc_channel::ipc::{IpcBytesReceiver, IpcBytesSender, IpcSharedMemory};
 use pixels::PixelFormat;
 use std::borrow::Cow;
 use std::fmt;
@@ -61,8 +59,6 @@ pub enum WebGLMsg {
     /// The WR client should not change the shared texture content until the Unlock call.
     /// Currently OpenGL Sync Objects are used to implement the synchronization mechanism.
     Lock(WebGLContextId, WebGLSender<(u32, Size2D<i32>, usize)>),
-    /// Lock(), but unconditionally IPC (used by webxr)
-    LockIPC(WebGLContextId, IpcSender<(u32, Size2D<i32>, usize)>),
     /// Unlocks a specific WebGLContext. Unlock messages are used for a correct synchronization
     /// with WebRender external image API.
     /// The WR unlocks a context when it finished reading the shared texture contents.
@@ -185,39 +181,6 @@ impl WebGLMsgSender {
     pub fn send_dom_to_texture(&self, command: DOMToTextureCommand) -> WebGLSendResult {
         self.sender.send(WebGLMsg::DOMToTextureCommand(command))
     }
-
-    pub fn webxr_external_image_api(&self) -> impl webxr_api::WebGLExternalImageApi {
-        SerializableWebGLMsgSender {
-            ctx_id: self.ctx_id,
-            sender: self.sender.to_ipc(),
-        }
-    }
-}
-
-// WegGLMsgSender isn't actually serializable, despite what it claims.
-#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize)]
-struct SerializableWebGLMsgSender {
-    ctx_id: WebGLContextId,
-    #[ignore_malloc_size_of = "channels are hard"]
-    sender: IpcSender<WebGLMsg>,
-}
-
-#[typetag::serde]
-impl webxr_api::WebGLExternalImageApi for SerializableWebGLMsgSender {
-    fn lock(&self) -> Result<(GLuint, Size2D<i32>, GLsync), webxr_api::Error> {
-        let (sender, receiver) = ipc::channel().or(Err(webxr_api::Error::CommunicationError))?;
-        self.sender
-            .send(WebGLMsg::LockIPC(self.ctx_id, sender))
-            .or(Err(webxr_api::Error::CommunicationError))?;
-        let (texture, size, sync) = receiver
-            .recv()
-            .or(Err(webxr_api::Error::CommunicationError))?;
-        Ok((texture, size, sync as GLsync))
-    }
-
-    fn unlock(&self) {
-        let _ = self.sender.send(WebGLMsg::Unlock(self.ctx_id));
-    }
 }
 
 #[derive(Deserialize, Serialize)]
diff --git a/components/script/dom/webglrenderingcontext.rs b/components/script/dom/webglrenderingcontext.rs
index 743a2adec84..3a273f3cfa3 100644
--- a/components/script/dom/webglrenderingcontext.rs
+++ b/components/script/dom/webglrenderingcontext.rs
@@ -328,6 +328,10 @@ impl WebGLRenderingContext {
         self.webgl_sender.clone()
     }
 
+    pub fn context_id(&self) -> WebGLContextId {
+        self.webgl_sender.context_id()
+    }
+
     #[inline]
     pub fn send_command(&self, command: WebGLCommand) {
         self.webgl_sender
@@ -4377,8 +4381,4 @@ impl WebGLMessageSender {
     pub fn send_dom_to_texture(&self, command: DOMToTextureCommand) -> WebGLSendResult {
         self.wake_after_send(|| self.sender.send_dom_to_texture(command))
     }
-
-    pub fn webxr_external_image_api(&self) -> impl webxr_api::WebGLExternalImageApi {
-        self.sender.webxr_external_image_api()
-    }
 }
diff --git a/components/script/dom/xr.rs b/components/script/dom/xr.rs
index d24e8f144cd..8deead58b92 100644
--- a/components/script/dom/xr.rs
+++ b/components/script/dom/xr.rs
@@ -108,18 +108,6 @@ impl Into<SessionMode> for XRSessionMode {
 impl XRMethods for XR {
     /// https://immersive-web.github.io/webxr/#dom-xr-supportssessionmode
     fn SupportsSession(&self, mode: XRSessionMode) -> Rc<Promise> {
-        #[derive(serde::Serialize, serde::Deserialize)]
-        pub struct SupportsSession {
-            sender: IpcSender<bool>,
-        }
-
-        #[typetag::serde]
-        impl webxr_api::SessionSupportCallback for SupportsSession {
-            fn callback(&mut self, result: Result<(), XRError>) {
-                let _ = self.sender.send(result.is_ok());
-            }
-        }
-
         // XXXManishearth this should select an XR device first
         let promise = Promise::new(&self.global());
         let mut trusted = Some(TrustedPromise::new(promise.clone()));
@@ -139,13 +127,13 @@ impl XRMethods for XR {
                     error!("supportsSession callback called twice!");
                     return;
                 };
-                let message = if let Ok(message) = message.to() {
+                let message: Result<(), webxr_api::Error> = if let Ok(message) = message.to() {
                     message
                 } else {
                     error!("supportsSession callback given incorrect payload");
                     return;
                 };
-                if message {
+                if let Ok(()) = message {
                     let _ = task_source.queue_with_canceller(trusted.resolve_task(()), &canceller);
                 } else {
                     let _ = task_source
@@ -155,7 +143,7 @@ impl XRMethods for XR {
         );
         window
             .webxr_registry()
-            .supports_session(mode.into(), SupportsSession { sender });
+            .supports_session(mode.into(), sender);
 
         promise
     }
@@ -167,17 +155,6 @@ impl XRMethods for XR {
         _: &XRSessionInit,
         comp: InCompartment,
     ) -> Rc<Promise> {
-        #[derive(serde::Serialize, serde::Deserialize)]
-        pub struct RequestSession {
-            sender: IpcSender<Result<Session, XRError>>,
-        }
-
-        #[typetag::serde]
-        impl webxr_api::SessionRequestCallback for RequestSession {
-            fn callback(&mut self, result: Result<Session, XRError>) {
-                let _ = self.sender.send(result);
-            }
-        }
         let promise = Promise::new_in_current_compartment(&self.global(), comp);
         if mode != XRSessionMode::Immersive_vr {
             promise.reject_error(Error::NotSupported);
@@ -206,7 +183,7 @@ impl XRMethods for XR {
                 // router doesn't know this is only called once
                 let trusted = trusted.take().unwrap();
                 let this = this.clone();
-                let message = if let Ok(message) = message.to() {
+                let message: Result<Session, webxr_api::Error> = if let Ok(message) = message.to() {
                     message
                 } else {
                     error!("requestSession callback given incorrect payload");
@@ -220,9 +197,7 @@ impl XRMethods for XR {
                 );
             }),
         );
-        window
-            .webxr_registry()
-            .request_session(mode.into(), RequestSession { sender });
+        window.webxr_registry().request_session(mode.into(), sender);
 
         promise
     }
diff --git a/components/script/dom/xrsession.rs b/components/script/dom/xrsession.rs
index 9542486f3ae..0a9712bb92b 100644
--- a/components/script/dom/xrsession.rs
+++ b/components/script/dom/xrsession.rs
@@ -124,18 +124,6 @@ impl XRSession {
     }
 
     fn attach_event_handler(&self) {
-        #[derive(serde::Serialize, serde::Deserialize)]
-        pub struct EventCallback {
-            sender: IpcSender<XREvent>,
-        }
-
-        #[typetag::serde]
-        impl webxr_api::EventCallback for EventCallback {
-            fn callback(&mut self, event: XREvent) {
-                let _ = self.sender.send(event);
-            }
-        }
-
         let this = Trusted::new(self);
         let global = self.global();
         let window = global.as_window();
@@ -143,6 +131,7 @@ impl XRSession {
             .task_manager()
             .dom_manipulation_task_source_with_canceller();
         let (sender, receiver) = ipc::channel(global.time_profiler_chan().clone()).unwrap();
+
         ROUTER.add_route(
             receiver.to_opaque(),
             Box::new(move |message| {
@@ -157,9 +146,7 @@ impl XRSession {
         );
 
         // request animation frame
-        self.session
-            .borrow_mut()
-            .set_event_callback(EventCallback { sender });
+        self.session.borrow_mut().set_event_dest(sender);
     }
 
     fn event_callback(&self, event: XREvent) {
@@ -195,13 +182,10 @@ impl XRSession {
             // Step 6-7: XXXManishearth handle inlineVerticalFieldOfView
 
             // XXXManishearth handle inline sessions and composition disabled flag
-            let layer = pending.GetBaseLayer();
-            if let Some(layer) = layer {
-                let mut session = self.session.borrow_mut();
-                session.update_webgl_external_image_api(
-                    layer.Context().webgl_sender().webxr_external_image_api(),
-                );
-            }
+            let context = pending
+                .GetBaseLayer()
+                .map(|layer| layer.Context().context_id().0);
+            self.session.borrow_mut().set_webgl_context(context);
         }
 
         // Step 2
@@ -289,18 +273,6 @@ impl XRSessionMethods for XRSession {
 
     /// https://immersive-web.github.io/webxr/#dom-xrsession-requestanimationframe
     fn RequestAnimationFrame(&self, callback: Rc<XRFrameRequestCallback>) -> i32 {
-        #[derive(serde::Serialize, serde::Deserialize)]
-        pub struct FrameCallback {
-            sender: IpcSender<(f64, Frame)>,
-        }
-
-        #[typetag::serde]
-        impl webxr_api::FrameRequestCallback for FrameCallback {
-            fn callback(&mut self, time: f64, frame: Frame) {
-                let _ = self.sender.send((time, frame));
-            }
-        }
-
         // queue up RAF callback, obtain ID
         let raf_id = self.next_raf_id.get();
         self.next_raf_id.set(raf_id + 1);
@@ -334,9 +306,7 @@ impl XRSessionMethods for XRSession {
         let sender = self.raf_sender.borrow().clone().unwrap();
 
         // request animation frame
-        self.session
-            .borrow_mut()
-            .request_animation_frame(FrameCallback { sender });
+        self.session.borrow_mut().request_animation_frame(sender);
 
         raf_id
     }
diff --git a/components/script/dom/xrtest.rs b/components/script/dom/xrtest.rs
index c8f45b75b4f..3c376366faf 100644
--- a/components/script/dom/xrtest.rs
+++ b/components/script/dom/xrtest.rs
@@ -73,20 +73,6 @@ impl XRTest {
 impl XRTestMethods for XRTest {
     /// https://github.com/immersive-web/webxr-test-api/blob/master/explainer.md
     fn SimulateDeviceConnection(&self, init: &FakeXRDeviceInit) -> Rc<Promise> {
-        #[derive(serde::Serialize, serde::Deserialize)]
-        pub struct MockDevice {
-            sender: IpcSender<Result<IpcSender<MockDeviceMsg>, XRError>>,
-        }
-
-        #[typetag::serde]
-        impl webxr_api::MockDeviceCallback for MockDevice {
-            fn callback(&mut self, result: Result<IpcSender<MockDeviceMsg>, XRError>) {
-                self.sender
-                    .send(result)
-                    .expect("mock device callback failed");
-            }
-        }
-
         let p = Promise::new(&self.global());
 
         if !init.supportsImmersive || self.session_started.get() {
@@ -166,7 +152,7 @@ impl XRTestMethods for XRTest {
         );
         window
             .webxr_registry()
-            .simulate_device_connection(init, MockDevice { sender });
+            .simulate_device_connection(init, sender);
 
         p
     }
diff --git a/components/servo/lib.rs b/components/servo/lib.rs
index d94700f11fe..544517e7e7a 100644
--- a/components/servo/lib.rs
+++ b/components/servo/lib.rs
@@ -418,22 +418,26 @@ where
 
         // Initialize WebGL Thread entry point.
         let webgl_result = gl_factory.map(|factory| {
-            let (webgl_threads, thread_data, image_handler, output_handler) = WebGLThreads::new(
-                factory,
-                window.gl(),
-                webrender_api_sender.clone(),
-                webvr_compositor.map(|c| c as Box<_>),
-                external_images.clone(),
-                if run_webgl_on_main_thread {
-                    ThreadMode::MainThread(embedder.create_event_loop_waker())
-                } else {
-                    ThreadMode::OffThread
-                },
-            );
+            let (webgl_threads, thread_data, webxr_handler, image_handler, output_handler) =
+                WebGLThreads::new(
+                    factory,
+                    window.gl(),
+                    webrender_api_sender.clone(),
+                    webvr_compositor.map(|c| c as Box<_>),
+                    external_images.clone(),
+                    if run_webgl_on_main_thread {
+                        ThreadMode::MainThread(embedder.create_event_loop_waker())
+                    } else {
+                        ThreadMode::OffThread
+                    },
+                );
 
             // Set webrender external image handler for WebGL textures
             external_image_handlers.set_handler(image_handler, WebrenderImageHandlerType::WebGL);
 
+            // Set webxr external image handler for WebGL textures
+            webxr_main_thread.set_webgl(webxr_handler);
+
             // Set DOM to texture handler, if enabled.
             if let Some(output_handler) = output_handler {
                 webrender.set_output_image_handler(output_handler);