Init XR present on XR::RequestSession() with empty context

components/script/dom/vrdisplay.rs

@@ -688,12 +688,12 @@ impl VRDisplay {
 // XR stuff
 // XXXManishearth eventually we should share as much logic as possible
 impl VRDisplay {
-    pub fn xr_present(&self, session: &XRSession, ctx: &WebGLRenderingContext) {
+    pub fn xr_present(&self, session: &XRSession, ctx: Option<&WebGLRenderingContext>) {
         let layer_bounds = WebVRLayer::default();
         self.xr_session.set(Some(session));
         if self.presenting.get() {
             *self.layer.borrow_mut() = layer_bounds;
-            self.layer_ctx.set(Some(&ctx));
+            self.layer_ctx.set(ctx);
             return;
         }
 
@@ -709,7 +709,7 @@ impl VRDisplay {
 
         if let Ok(()) = receiver.recv().unwrap() {
             *self.layer.borrow_mut() = layer_bounds;
-            self.layer_ctx.set(Some(&ctx));
+            self.layer_ctx.set(ctx);
             self.init_present();
         }
     }

components/script/dom/xr.rs

@@ -95,10 +95,9 @@ impl XRMethods for XR {
         }
 
         let session = XRSession::new(&self.global(), &displays[0]);
+        // XXXManishearth we should actually xr_present() here instead of
+        // in XRSession::new, and resolve a promise based on it
         promise.resolve_native(&session);
-        // whether or not we should initiate presentation is unclear
-        // https://github.com/immersive-web/webxr/issues/453
-
         promise
     }
 }

components/script/dom/xrsession.rs

@@ -37,11 +37,13 @@ impl XRSession {
     }
 
     pub fn new(global: &GlobalScope, display: &VRDisplay) -> DomRoot<XRSession> {
-        reflect_dom_object(
+        let ret = reflect_dom_object(
             Box::new(XRSession::new_inherited(display)),
             global,
             XRSessionBinding::Wrap,
-        )
+        );
+        ret.display.xr_present(&ret, None);
+        ret
     }
 }
 
@@ -76,7 +78,7 @@ impl XRSessionMethods for XRSession {
         self.base_layer.set(layer);
         if let Some(layer) = layer {
             let layer = layer.downcast::<XRWebGLLayer>().unwrap();
-            self.display.xr_present(&self, &layer.Context());
+            self.display.xr_present(&self, Some(&layer.Context()));
         } else {
             // steps unknown
             // https://github.com/immersive-web/webxr/issues/453