Explicitly spec out native origins (#621)

Manishearth · toji · commit 8c7a85c1a6af · 2019-05-06T23:10:27.000-07:00
Adds native origins for input spaces, viewerSpace, identity, and position-disabled spaces. Specifies that the native origin of identity spaces is constant when there is no tracking data.
diff --git a/index.bs b/index.bs
@@ -495,7 +495,7 @@ The <dfn attribute for="XRSession">environmentBlendMode</dfn> attribute returns
 
 NOTE: Most Virtual Reality devices exhibit {{XREnvironmentBlendMode/opaque}} blending behavior. Augmented Reality devices that use transparent optical elements frequently exhibit {{XREnvironmentBlendMode/additive}} blending behavior, and Augmented Reality devices that use passthrough cameras frequently exhibit {{XREnvironmentBlendMode/alpha-blend}} blending behavior.
 
-The <dfn attribute for="XRSession">viewerSpace</dfn> attribute is an {{XRSpace}} which tracks the pose of the [=viewer=].
+The <dfn attribute for="XRSession">viewerSpace</dfn> attribute is an {{XRSpace}} with a [=native origin=] that tracks the pose of the [=viewer=].
 
 NOTE: For any given {{XRFrame}} calling {{XRFrame/getPose()}} with the {{XRSession/viewerSpace}} and any {{XRReferenceSpace}} will return the same pose (without the {{views}} array) as calling {{XRFrame/getViewerPose()}} with the same {{XRReferenceSpace}}.
 
@@ -780,9 +780,9 @@ Each {{XRReferenceSpace}} has a <dfn for="XRReferenceSpace">type</dfn>, which is
 
 An {{XRReferenceSpace}} is most frequently obtained by calling {{XRSession/requestReferenceSpace()}}, which creates an instance of an {{XRReferenceSpace}} or an interface extending it, determined by the {{XRReferenceSpaceType}} enum value passed into the call. The type indicates the tracking behavior that the reference space will exhibit:
 
-  - Passing a type of <dfn enum-value for="XRReferenceSpaceType">identity</dfn> creates an {{XRReferenceSpace}} instance. It represents a reference space where the [=viewer=] is always at the [=native origin=]. Only the {{XRSession/viewerSpace}} and {{XRInputSource/targetRaySpace}}'s of {{XRInputSource}}'s with an {{XRInputSource/targetRayMode}} of {{XRTargetRayMode/screen}} can be spatially related to an {{identity}} reference space.
+  - Passing a type of <dfn enum-value for="XRReferenceSpaceType">identity</dfn> creates an {{XRReferenceSpace}} instance. It represents a tracking space with a [=native origin=] that tracks the position and orientation of the [=viewer=]. For {{XRSession}}s without tracking data, the [=native origin=] stays constant. Only the {{XRSession/viewerSpace}} and {{XRInputSource/targetRaySpace}}'s of {{XRInputSource}}'s with an {{XRInputSource/targetRayMode}} of {{XRTargetRayMode/screen}} can be spatially related to an {{identity}} reference space.
 
-  - Passing a type of <dfn enum-value for="XRReferenceSpaceType">position-disabled</dfn> creates an {{XRReferenceSpace}} instance. It represents a tracking space where orientation is tracked but the [=viewer=]s position is always at the [=native origin=].
+  - Passing a type of <dfn enum-value for="XRReferenceSpaceType">position-disabled</dfn> creates an {{XRReferenceSpace}} instance.  It represents a tracking space with a [=native origin=] that tracks the position of the [=viewer=], with a constant orientation initialized based on the conventions of the underlying [=/XR device=]. It can be used to create experiences where the movement of the user is disregarded, as it will not report changes in position when used with {{XRFrame/getViewerPose()}}.
 
   - Passing a type of <dfn enum-value for="XRReferenceSpaceType">eye-level</dfn> creates an {{XRReferenceSpace}} instance. It represents a tracking space with a [=native origin=] near the user's head at the time of creation. The exact position and orientation will be initialized based on the conventions of the underlying platform. When using this reference space the user is not expected to move beyond their initial position much, if at all, and tracking is optimized for that purpose. For devices with [=6DoF=] tracking, {{eye-level}} reference spaces should emphasize keeping the origin stable relative to the user's environment.
 
@@ -1157,9 +1157,9 @@ The <dfn attribute for="XRInputSource">targetRayMode</dfn> attribute describes t
 
 Note: Some input sources, like an {{XRInputSource}} with {{targetRayMode}} set to {{screen}}, will only be added to the session's [=list of active input sources=] immediately before the {{selectstart}} event, and removed from the session's [=list of active input sources=] immediately after the {{selectend}} event.
 
-The <dfn attribute for="XRInputSource">targetRaySpace</dfn> attribute is an {{XRSpace}} that tracks the pose of the preferred pointing ray of the {{XRInputSource}}, as defined by the {{targetRayMode}}.
+The <dfn attribute for="XRInputSource">targetRaySpace</dfn> attribute is an {{XRSpace}} that has a [=native origin=] tracking the position and orientation of the preferred pointing ray of the {{XRInputSource}}, as defined by the {{targetRayMode}}.
 
-The <dfn attribute for="XRInputSource">gripSpace</dfn> attribute is an {{XRSpace}} that tracks the pose that should be used to render virtual objects such that they appear to be held in the user's hand. If the user were to hold a straight rod, this {{XRSpace}} places the origin at the centroid of their curled fingers and where the <code>-Z</code> axis points along the length of the rod towards their thumb. The <code>X</code> axis is perpendicular to the back of the hand being described, with back of the users right hand pointing towards <code>+X</code> and the back of the user's left hand pointing towards <code>-X</code>. The <code>Y</code> axis is implied by the relationship between the <code>X</code> and <code>Z</code> axis, with <code>+Y</code> roughly pointing in the direction of the user's arm.
+The <dfn attribute for="XRInputSource">gripSpace</dfn> attribute is an {{XRSpace}} that has a [=native origin=] tracking to the pose that should be used to render virtual objects such that they appear to be held in the user's hand. If the user were to hold a straight rod, this {{XRSpace}} places the [=native origin=] at the centroid of their curled fingers and where the <code>-Z</code> axis points along the length of the rod towards their thumb. The <code>X</code> axis is perpendicular to the back of the hand being described, with back of the users right hand pointing towards <code>+X</code> and the back of the user's left hand pointing towards <code>-X</code>. The <code>Y</code> axis is implied by the relationship between the <code>X</code> and <code>Z</code> axis, with <code>+Y</code> roughly pointing in the direction of the user's arm.
 
 The {{gripSpace}} MUST be <code>null</code> if the input source isn't inherently trackable such as for input sources with a {{targetRayMode}} of {{XRTargetRayMode/gaze}} or {{XRTargetRayMode/screen}}.
 
