Improve getViewerPose()

components/script/dom/webidls/XRFrame.webidl

@@ -8,6 +8,6 @@
 interface XRFrame {
   readonly attribute XRSession session;
 
-  XRViewerPose? getViewerPose(optional XRReferenceSpace referenceSpace);
+  XRViewerPose? getViewerPose(XRReferenceSpace referenceSpace);
   // XRInputPose? getInputPose(XRInputSource inputSource, optional XRReferenceSpace referenceSpace);
 };

components/script/dom/xrframe.rs

@@ -5,11 +5,13 @@
 use crate::dom::bindings::codegen::Bindings::XRFrameBinding;
 use crate::dom::bindings::codegen::Bindings::XRFrameBinding::XRFrameMethods;
 use crate::dom::bindings::codegen::Bindings::XRViewBinding::XREye;
+use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::reflector::{reflect_dom_object, DomObject, Reflector};
 use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::xrreferencespace::XRReferenceSpace;
 use crate::dom::xrsession::XRSession;
+use crate::dom::xrstationaryreferencespace::XRStationaryReferenceSpace;
 use crate::dom::xrview::XRView;
 use crate::dom::xrviewerpose::XRViewerPose;
 use dom_struct::dom_struct;
@@ -52,17 +54,17 @@ impl XRFrameMethods for XRFrame {
     }
 
     /// https://immersive-web.github.io/webxr/#dom-xrframe-getviewerpose
-    fn GetViewerPose(&self, reference: Option<&XRReferenceSpace>) -> Option<DomRoot<XRViewerPose>> {
-        // We assume the reference space is eye level for now
-        // since it's the only one 3DOF devices support
-        if reference.is_some() {
-            // it's not possible to obtain a reference
-            // space at all yet
-            None
-        } else {
+    fn GetViewerPose(&self, reference: &XRReferenceSpace) -> Option<DomRoot<XRViewerPose>> {
+        if let Some(_) = reference.downcast::<XRStationaryReferenceSpace>() {
+            // For 3DOF devices all three kinds of reference spaces are identical
+            // FIXME(#23070, Manishearth) support originOffset
             let left = XRView::new(&self.global(), &self.session, XREye::Left, &self.data);
             let right = XRView::new(&self.global(), &self.session, XREye::Right, &self.data);
             Some(XRViewerPose::new(&self.global(), &left, &right))
+        } else {
+            // FIXME(#23070, Manishearth) support identity reference spaces
+            // depends on https://github.com/immersive-web/webxr/issues/565
+            None
         }
     }
 }

components/script/dom/xrsession.rs

@@ -124,6 +124,9 @@ impl XRSessionMethods for XRSession {
 
         // https://immersive-web.github.io/webxr/#create-a-reference-space
 
+        // XXXManishearth reject based on session type
+        // https://github.com/immersive-web/webxr/blob/master/spatial-tracking-explainer.md#practical-usage-guidelines
+
         match options.type_ {
             XRReferenceSpaceType::Identity => {
                 p.resolve_native(&XRReferenceSpace::identity(