inverse attribute always returns the same object (#586)

toji · web-flow · commit 9553f1cda6f9 · 2019-04-15T12:36:34.000-07:00
Fixes #576. Specifies that the object returned by `XRRigidTransform`'s `inverse` attribute must always be the same JS object and, furthermore, the `inverse` of a transform returned by `inverse` must be the originating transform.
diff --git a/index.bs b/index.bs
@@ -963,7 +963,7 @@ interface XRRigidTransform {
   readonly attribute DOMPointReadOnly position;
   readonly attribute DOMPointReadOnly orientation;
   readonly attribute Float32Array matrix;
-  readonly attribute XRRigidTransform inverse;
+  [SameObject] readonly attribute XRRigidTransform inverse;
 };
 </pre>
 
@@ -988,7 +988,7 @@ The <dfn attribute for="XRRigidTransform">orientation</dfn> attribute is a quate
 
 The <dfn attribute for="XRRigidTransform">matrix</dfn> attribute returns the transform described by the {{XRRigidTransform/position}} and {{XRRigidTransform/orientation}} attributes as a [=matrix=]. This attribute SHOULD be lazily evaluated.
 
-The <dfn attribute for="XRRigidTransform">inverse</dfn> attribute returns a {{XRRigidTransform}} which, if applied to an object that had previously been transformed by the original {{XRRigidTransform}}, would undo the transform and return the object to it's initial pose. This attribute SHOULD be lazily evaluated.
+The <dfn attribute for="XRRigidTransform">inverse</dfn> attribute returns a {{XRRigidTransform}} which, if applied to an object that had previously been transformed by the original {{XRRigidTransform}}, would undo the transform and return the object to its initial pose. This attribute SHOULD be lazily evaluated. The {{XRRigidTransform}} returned by {{inverse}} MUST return the originating {{XRRigidTransform}} as its {{inverse}}.
 
 An {{XRRigidTransform}} with a {{XRRigidTransform/position}} of <code>{ x: 0, y: 0, z: 0 w: 1 }</code> and an {{XRRigidTransform/orientation}} of <code>{ x: 0, y: 0, z: 0, w: 1 }</code> is known as an <dfn>identity transform</dfn>.
 
diff --git a/spatial-tracking-explainer.md b/spatial-tracking-explainer.md
@@ -434,7 +434,7 @@ interface XRRigidTransform {
   readonly attribute DOMPointReadOnly position;
   readonly attribute DOMPointReadOnly orientation;
   readonly attribute Float32Array matrix;
-  readonly attribute XRRigidTransform inverse;
+  [SameObject] readonly attribute XRRigidTransform inverse;
 };
 
 [SecureContext, Exposed=Window,
