Explicitly spec out when requestReferenceSpace() can reject queries (#651)

Manishearth · toji · commit 13a978f45ff2 · 2019-05-17T14:45:35.000-07:00
Provides a more explicit algorithm for determining if a given `XRReferenceSpaceType` is supported for a given `XRSession`. It's anticipated that this criteria will be expanded in the future as we finalize privacy considerations, but for now it's focused on the device capabilities.
diff --git a/index.bs b/index.bs
@@ -837,11 +837,26 @@ When an {{XRReferenceSpace}} is requested, the user agent MUST <dfn>create a ref
 
   1. Let |session| be the {{XRSession}} object that requested creation of a reference space.
   1. Let |type| be set to the {{XRReferenceSpaceType}} passed to {{requestReferenceSpace()}}.
-  1. If |type| is {{bounded-floor}}, let |referenceSpace| be a new {{XRBoundedReferenceSpace}}.
-  1. Else let |referenceSpace| be a new {{XRReferenceSpace}}.
-  1. Initialize |referenceSpace|'s [=XRReferenceSpace/type=] to be |type|.
-  1. Initialize [=XRSpace/session=] to be |session|.
-  1. Return |referenceSpace|.
+  1. If the [=reference space is supported=] for |type| and |session|, run the following steps:
+    1. If |type| is {{bounded-floor}}, let |referenceSpace| be a new {{XRBoundedReferenceSpace}}.
+    1. Else let |referenceSpace| be a new {{XRReferenceSpace}}.
+    1. Initialize |referenceSpace|'s [=XRReferenceSpace/type=] to be |type|.
+    1. Initialize |referenceSpace|'s [=XRSpace/session=] to be |session|.
+    1. Return |referenceSpace|
+  1. Else, return <code>null</code>.
+
+</div>
+
+<div class="algorithm" data-algorithm="reference-space-supported">
+To check if a <dfn>reference space is supported</dfn> for a given reference space type |type| and {{XRSession}} |session|, run the following steps:
+
+
+  1. If |type| is {{inline}}, return <code>true</code>.
+  1. If |type| is {{local}} or {{local-floor}}, and |session| is an [=immersive session=], return <code>true</code>.
+  1. If |type| is {{local}} or {{local-floor}}, and the [=/XR device=] supports reporting orientation data, return <code>true</code>.
+  1. If |type| is {{bounded-floor}} and |session| is an [=immersive session=], return if [=bounded reference spaces are supported=] by the [=/XR device=].
+  1. If |type| is {{unbounded}}, |session| is an [=immersive session=], and the [=/XR device=] supports stable tracking near the user over an unlimited distance, return <code>true</code>.
+  1. Return <code>false</code>.
 
 </div>
 
@@ -877,6 +892,15 @@ Each {{XRBoundedReferenceSpace}} has a <dfn for="XRBoundedReferenceSpace">native
 
 The <dfn attribute for="XRBoundedReferenceSpace">boundsGeometry</dfn> attribute is an array of {{DOMPointReadOnly}}s such that each entry is equal to the entry in the {{XRBoundedReferenceSpace}}'s [=XRBoundedReferenceSpace/native bounds geometry=] premultiplied by the {{XRRigidTransform/inverse}} of the [=XRSpace/origin offset=]. In other words, it provides the same border in {{XRBoundedReferenceSpace}} coordinates relative to the [=XRSpace/effective origin=].
 
+
+<div class="algorithm" data-algorithm="bounded-space-supported">
+To check if <dfn>bounded reference spaces are supported</dfn> run the following steps:
+    1. If the [=/XR device=] cannot report boundaries, return false.
+    1. If the [=/XR device=] cannot identify the height of the user's physical floor, return false.
+    1. Return true.
+</div>
+
+
 Note: Content should not require the user to move beyond the {{boundsGeometry}}. It is possible for the user to move beyond the bounds if their physical surroundings allow for it, resulting in position values outside of the polygon they describe. This is not an error condition and should be handled gracefully by page content.
 
 Note: Content generally should not provide a visualization of the {{boundsGeometry}}, as it's the user agent's responsibility to ensure that safety critical information is provided to the user.
