Auto merge of #23159 - Manishearth:rigid-transforms, r=asajeffrey

Update XR code to use rigid transforms and new pose/transform stuff from the spec

This updates our XR code to use euclid's new [RigidTransform3D type](https://github.com/servo/euclid/pull/328), which is more efficent and convenient to work with.

It additionally brings us up to speed with the spec:

 - `XRViewerPose` was made a subclass of `XRPose` (https://github.com/immersive-web/webxr/pull/496)
 - `XRView.viewMatrix` was removed in favor of `XRRigidTransform.inverse.matrix` (https://github.com/immersive-web/webxr/pull/531)
 - `XRRigidTransform.inverse` is an attribute (https://github.com/immersive-web/webxr/pull/560)
 - `XRRigidTransform` now validates positions in its constructor (https://github.com/immersive-web/webxr/pull/568)

Furthermore, it adds support for `XRRigidTransform.matrix`.

While fixing this I also noticed that our view matrix code was incorrect, we calculated view matrices as `pose.to_column_major_array()`, whereas it *should* be `pose.inverse().to_row_major_array()` (since Euclid uses row vectors, whenever the spec says it wants a column major array we should use `.to_row_major_array()` since all web specs implicitly use column vectors). For 3DOF devices poses are mostly rotations anyway, so the effective transpose behaved _like_ an inversion, but was incorrect.

This PR gets rid of `view.viewMatrix` anyway, however I felt like I should mention this discrepancy, since otherwise the replacement of `view.viewMatrix` with `view.transform.inverse.matrix` doesn't make sense

r? @jdm

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/23159)
<!-- Reviewable:end -->

1 files changed, 18 insertions, 17 deletions

diff --git a/components/script/dom/xrview.rs b/components/script/dom/xrview.rs
index 355177880a8..a2eee03581d 100644
--- a/components/script/dom/xrview.rs
+++ b/components/script/dom/xrview.rs
@@ -8,9 +8,10 @@ use crate::dom::bindings::reflector::{reflect_dom_object, Reflector};
 use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::vrframedata::create_typed_array;
+use crate::dom::xrrigidtransform::XRRigidTransform;
 use crate::dom::xrsession::XRSession;
 use dom_struct::dom_struct;
-use euclid::Transform3D;
+use euclid::{RigidTransform3D, Vector3D};
 use js::jsapi::{Heap, JSContext, JSObject};
 use std::ptr::NonNull;
 use webvr_traits::WebVRFrameData;
@@ -22,16 +23,18 @@ pub struct XRView {
     eye: XREye,
     proj: Heap<*mut JSObject>,
     view: Heap<*mut JSObject>,
+    transform: Dom<XRRigidTransform>,
 }
 
 impl XRView {
-    fn new_inherited(session: &XRSession, eye: XREye) -> XRView {
+    fn new_inherited(session: &XRSession, transform: &XRRigidTransform, eye: XREye) -> XRView {
         XRView {
             reflector_: Reflector::new(),
             session: Dom::from_ref(session),
             eye,
             proj: Heap::default(),
             view: Heap::default(),
+            transform: Dom::from_ref(transform),
         }
     }
 
@@ -40,15 +43,9 @@ impl XRView {
         global: &GlobalScope,
         session: &XRSession,
         eye: XREye,
-        pose: &Transform3D<f64>,
+        pose: &RigidTransform3D<f64>,
         data: &WebVRFrameData,
     ) -> DomRoot<XRView> {
-        let ret = reflect_dom_object(
-            Box::new(XRView::new_inherited(session, eye)),
-            global,
-            XRViewBinding::Wrap,
-        );
-
         let vr_display = session.display();
 
         // XXXManishearth compute and cache projection matrices on the Display
@@ -64,14 +61,19 @@ impl XRView {
             )
         };
 
-        let offset =
-            Transform3D::create_translation(offset[0] as f64, offset[1] as f64, offset[2] as f64);
-        let view = pose.post_mul(&offset).cast().to_column_major_array();
+        let offset = Vector3D::new(offset[0] as f64, offset[1] as f64, offset[2] as f64);
+        let transform = pose.post_mul(&offset.into());
+        let transform = XRRigidTransform::new(global, transform);
+
+        let ret = reflect_dom_object(
+            Box::new(XRView::new_inherited(session, &transform, eye)),
+            global,
+            XRViewBinding::Wrap,
+        );
 
         let cx = global.get_cx();
         unsafe {
             create_typed_array(cx, proj, &ret.proj);
-            create_typed_array(cx, &view, &ret.view);
         }
         ret
     }
@@ -93,9 +95,8 @@ impl XRViewMethods for XRView {
         NonNull::new(self.proj.get()).unwrap()
     }
 
-    #[allow(unsafe_code)]
-    /// https://immersive-web.github.io/webxr/#dom-xrview-projectionmatrix
-    unsafe fn ViewMatrix(&self, _cx: *mut JSContext) -> NonNull<JSObject> {
-        NonNull::new(self.view.get()).unwrap()
+    /// https://immersive-web.github.io/webxr/#dom-xrview-transform
+    fn Transform(&self) -> DomRoot<XRRigidTransform> {
+        DomRoot::from_ref(&self.transform)
     }
 }