Update XRRay vector constructor to use correct webidl semantics (#85)

* Fix webidl for XRRay

* Update XRRay vector constructor to use correct webidl semantics

Fixes #84

This adds a new initializer type so that the defaults work correctly.

* Throw error for non-1 w coordinate for XRRay constructor's position

* Throw on nonzero direction.w

Author: Manishearth

index.bs

@@ -542,6 +542,20 @@ When the <dfn method for="XRFrame">getHitTestResultsForTransientInput(|hitTestSo
 Geometric primitives {#geometric-primitives}
 ====================
 
+XRRayDirectionInit {#xr-ray-direction-init-dictionary}
+--------------------
+
+An {{XRRayDirectionInit}} dictionary represents a direction vector to be passed to the {{XRRay(origin, direction)}} constructor.
+
+<script type="idl">
+dictionary XRRayDirectionInit {
+  double x = 0;
+  double y = 0;
+  double z = -1;
+  double w = 0;
+};
+</script>
+
 XRRay {#xrray-interface}
 -----
 
@@ -550,10 +564,10 @@ An {{XRRay}} is a geometric ray described by an {{XRRay/origin}} point and {{XRR
 An {{XRRay}} contains a <dfn for=XRRay>matrix</dfn> which is a [=/matrix=].
 
 <script type="idl">
-[SecureContext, Exposed=Window,
- Constructor(optional DOMPointInit origin, optional DOMPointInit direction),
- Constructor(XRRigidTransform transform)]
+[SecureContext, Exposed=Window]
 interface XRRay {
+  constructor(optional DOMPointInit origin = {}, optional XRRayDirectionInit direction = {});
+  constructor(XRRigidTransform transform);
   [SameObject] readonly attribute DOMPointReadOnly origin;
   [SameObject] readonly attribute DOMPointReadOnly direction;
   [SameObject] readonly attribute Float32Array matrix;
@@ -567,8 +581,11 @@ The <dfn constructor for="XRRay">XRRay(|origin|, |direction|)</dfn> constructor
   1. Let |ray| be a new {{XRRay}}.
   1. Initialize |ray|'s {{XRRay/origin}} to <code>{ x: 0.0, y: 0.0, z: 0.0, w: 1.0 }</code>.
   1. Initialize |ray|'s {{XRRay/direction}} to <code>{ x: 0.0, y: 0.0, z: -1.0, w: 0.0 }</code>.
-  1. If |origin| was set, initialize |ray|'s {{XRRay/origin}}’s {{DOMPointReadOnly/x}} value to |origin|'s x dictionary member, {{DOMPointReadOnly/y}} value to |origin|'s y dictionary member, and {{DOMPointReadOnly/z}} value to |origin|'s z dictionary member.
-  1. If |direction| was set, initialize |ray|'s {{XRRay/direction}}’s {{DOMPointReadOnly/x}} value to |direction|'s x dictionary member, {{DOMPointReadOnly/y}} value to |direction|'s y dictionary member, and {{DOMPointReadOnly/z}} value to |direction|'s z dictionary member.
+  1. If all of |direction|'s {{XRRayDirectionInit/x}}, {{XRRayDirectionInit/y}}, and {{XRRayDirectionInit/z}} are zero, throw a {{TypeError}} and abort these steps.
+  1. If |direction|'s {{XRRayDirectionInit/w}} is not 0.0, throw a {{TypeError}} and abort these steps.
+  1. If |origin|'s {{DOMPointInit/w}} is not 1.0, throw a {{TypeError}} and abort these steps.
+  1. Initialize |ray|'s {{XRRay/origin}}’s {{DOMPointReadOnly/x}} value to |origin|'s {{DOMPointInit/x}}, {{DOMPointReadOnly/y}} value to |origin|'s {{DOMPointInit/y}}, and {{DOMPointReadOnly/z}} value to |origin|'s {{DOMPointInit/z}}.
+  1. Initialize |ray|'s {{XRRay/direction}}’s {{DOMPointReadOnly/x}} value to |direction|'s {{XRRayDirectionInit/x}}, {{DOMPointReadOnly/y}} value to |direction|'s {{XRRayDirectionInit/y}}, and {{DOMPointReadOnly/z}} value to |direction|'s {{XRRayDirectionInit/z}}.
   1. [=Normalize=] the {{DOMPointReadOnly/x}}, {{DOMPointReadOnly/y}}, and {{DOMPointReadOnly/z}} components of |ray|'s {{XRRay/direction}}.
   1. Initialize |ray|'s [=XRRay/matrix=] to <code>null</code>.
   1. Return |ray|.