Handle erroring out when there are multiple immersive sessions

2 files changed, 59 insertions, 9 deletions

diff --git a/components/script/dom/vrdisplay.rs b/components/script/dom/vrdisplay.rs
index 6c4bea1568c..dd8f29195b7 100644
--- a/components/script/dom/vrdisplay.rs
+++ b/components/script/dom/vrdisplay.rs
@@ -4,6 +4,7 @@
 
 use crate::dom::bindings::callback::ExceptionHandling;
 use crate::dom::bindings::cell::DomRefCell;
+use crate::dom::bindings::codegen::Bindings::NavigatorBinding::NavigatorMethods;
 use crate::dom::bindings::codegen::Bindings::PerformanceBinding::PerformanceMethods;
 use crate::dom::bindings::codegen::Bindings::VRDisplayBinding;
 use crate::dom::bindings::codegen::Bindings::VRDisplayBinding::VRDisplayMethods;
@@ -13,6 +14,7 @@ use crate::dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGL
 use crate::dom::bindings::codegen::Bindings::WindowBinding::FrameRequestCallback;
 use crate::dom::bindings::codegen::Bindings::WindowBinding::WindowMethods;
 use crate::dom::bindings::codegen::Bindings::XRSessionBinding::XRFrameRequestCallback;
+use crate::dom::bindings::error::Error;
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::num::Finite;
 use crate::dom::bindings::refcounted::{Trusted, TrustedPromise};
@@ -347,6 +349,24 @@ impl VRDisplayMethods for VRDisplay {
             },
         };
 
+        // WebVR spec: Repeat calls while already presenting will update the VRLayers being displayed.
+        if self.presenting.get() {
+            *self.layer.borrow_mut() = layer_bounds;
+            self.layer_ctx.set(Some(&layer_ctx));
+            promise.resolve_native(&());
+            return promise;
+        }
+
+        let xr = self.global().as_window().Navigator().Xr();
+
+        if xr.pending_or_active_session() {
+            // WebVR spec doesn't mandate anything here, however
+            // the WebXR spec expects there to be only one immersive XR session at a time,
+            // and WebVR is deprecated
+            promise.reject_error(Error::InvalidState);
+            return promise;
+        }
+
         self.request_present(layer_bounds, Some(&layer_ctx), Some(promise.clone()), |p| {
             p.resolve_native(&())
         });
@@ -447,14 +467,6 @@ impl VRDisplay {
     ) where
         F: FnOnce(Rc<Promise>) + Send + 'static,
     {
-        // WebVR spec: Repeat calls while already presenting will update the VRLayers being displayed.
-        if self.presenting.get() {
-            *self.layer.borrow_mut() = layer_bounds;
-            self.layer_ctx.set(ctx);
-            promise.map(resolve);
-            return;
-        }
-
         // Request Present
         let (sender, receiver) = ipc::channel(self.global().time_profiler_chan().clone()).unwrap();
         self.webvr_thread()
@@ -557,6 +569,8 @@ impl VRDisplay {
 
     fn init_present(&self) {
         self.presenting.set(true);
+        let xr = self.global().as_window().Navigator().Xr();
+        xr.set_active_immersive_session(&self);
         let (sync_sender, sync_receiver) = webgl_channel().unwrap();
         *self.frame_data_receiver.borrow_mut() = Some(sync_receiver);
 
@@ -623,6 +637,8 @@ impl VRDisplay {
 
     fn stop_present(&self) {
         self.presenting.set(false);
+        let xr = self.global().as_window().Navigator().Xr();
+        xr.deactivate_session();
         *self.frame_data_receiver.borrow_mut() = None;
 
         let api_sender = self.layer_ctx.get().unwrap().webgl_sender();
diff --git a/components/script/dom/xr.rs b/components/script/dom/xr.rs
index 3e18ee0d279..13838ac2b20 100644
--- a/components/script/dom/xr.rs
+++ b/components/script/dom/xr.rs
@@ -10,7 +10,7 @@ use crate::dom::bindings::codegen::Bindings::XRBinding::{XRMethods, XRSessionMod
 use crate::dom::bindings::error::Error;
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::reflector::{reflect_dom_object, DomObject};
-use crate::dom::bindings::root::{Dom, DomRoot};
+use crate::dom::bindings::root::{Dom, DomRoot, MutNullableDom};
 use crate::dom::event::Event;
 use crate::dom::eventtarget::EventTarget;
 use crate::dom::gamepad::Gamepad;
@@ -23,6 +23,7 @@ use crate::dom::xrsession::XRSession;
 use dom_struct::dom_struct;
 use ipc_channel::ipc::IpcSender;
 use profile_traits::ipc;
+use std::cell::Cell;
 use std::rc::Rc;
 use webvr_traits::{WebVRDisplayData, WebVRDisplayEvent, WebVREvent, WebVRMsg};
 use webvr_traits::{WebVRGamepadData, WebVRGamepadEvent, WebVRGamepadState};
@@ -32,6 +33,8 @@ pub struct XR {
     eventtarget: EventTarget,
     displays: DomRefCell<Vec<Dom<VRDisplay>>>,
     gamepads: DomRefCell<Vec<Dom<Gamepad>>>,
+    pending_immersive_session: Cell<bool>,
+    active_immersive_session: MutNullableDom<VRDisplay>,
 }
 
 impl XR {
@@ -40,6 +43,8 @@ impl XR {
             eventtarget: EventTarget::new_inherited(),
             displays: DomRefCell::new(Vec::new()),
             gamepads: DomRefCell::new(Vec::new()),
+            pending_immersive_session: Cell::new(false),
+            active_immersive_session: Default::default(),
         }
     }
 
@@ -48,6 +53,26 @@ impl XR {
         root.register();
         root
     }
+
+    pub fn pending_or_active_session(&self) -> bool {
+        self.pending_immersive_session.get() || self.active_immersive_session.get().is_some()
+    }
+
+    pub fn set_pending(&self) {
+        self.pending_immersive_session.set(true)
+    }
+
+    pub fn set_active_immersive_session(&self, session: &VRDisplay) {
+        // XXXManishearth when we support non-immersive (inline) sessions we should
+        // ensure they never reach these codepaths
+        self.pending_immersive_session.set(false);
+        self.active_immersive_session.set(Some(session))
+    }
+
+    pub fn deactivate_session(&self) {
+        self.pending_immersive_session.set(false);
+        self.active_immersive_session.set(None)
+    }
 }
 
 impl Drop for XR {
@@ -79,6 +104,13 @@ impl XRMethods for XR {
             return promise;
         }
 
+        if self.pending_or_active_session() {
+            promise.reject_error(Error::InvalidState);
+            return promise;
+        }
+        // we set pending immersive session to true further down
+        // to handle rejections in a cleaner way
+
         let displays = self.get_displays();
 
         let displays = match displays {
@@ -94,6 +126,8 @@ impl XRMethods for XR {
             promise.reject_error(Error::Security);
         }
 
+        self.set_pending();
+
         let session = XRSession::new(&self.global(), &displays[0]);
         session.xr_present(promise.clone());
         promise