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

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1 files changed, 8 insertions, 29 deletions

diff --git a/components/script/dom/xrreferencespace.rs b/components/script/dom/xrreferencespace.rs
index 1c137d575ce..ed42d63b4be 100644
--- a/components/script/dom/xrreferencespace.rs
+++ b/components/script/dom/xrreferencespace.rs
@@ -7,14 +7,13 @@ use crate::dom::bindings::codegen::Bindings::XRReferenceSpaceBinding::XRReferenc
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::reflector::reflect_dom_object;
 use crate::dom::bindings::root::{DomRoot, MutDom};
-use crate::dom::dompointreadonly::DOMPointReadOnly;
-use crate::dom::window::Window;
+use crate::dom::globalscope::GlobalScope;
 use crate::dom::xrrigidtransform::XRRigidTransform;
 use crate::dom::xrsession::XRSession;
 use crate::dom::xrspace::XRSpace;
 use crate::dom::xrstationaryreferencespace::XRStationaryReferenceSpace;
 use dom_struct::dom_struct;
-use euclid::Transform3D;
+use euclid::RigidTransform3D;
 use webvr_traits::WebVRFrameData;
 
 #[dom_struct]
@@ -32,22 +31,7 @@ impl XRReferenceSpace {
     }
 
     #[allow(unused)]
-    pub fn new(
-        global: &Window,
-        session: &XRSession,
-        position: &DOMPointReadOnly,
-        orientation: &DOMPointReadOnly,
-    ) -> DomRoot<XRReferenceSpace> {
-        let transform = XRRigidTransform::new(global, position, orientation);
-        reflect_dom_object(
-            Box::new(XRReferenceSpace::new_inherited(session, &transform)),
-            global,
-            XRReferenceSpaceBinding::Wrap,
-        )
-    }
-
-    #[allow(unused)]
-    pub fn identity(global: &Window, session: &XRSession) -> DomRoot<XRReferenceSpace> {
+    pub fn identity(global: &GlobalScope, session: &XRSession) -> DomRoot<XRReferenceSpace> {
         let transform = XRRigidTransform::identity(global);
         reflect_dom_object(
             Box::new(XRReferenceSpace::new_inherited(session, &transform)),
@@ -71,30 +55,25 @@ impl XRReferenceSpaceMethods for XRReferenceSpace {
 
 impl XRReferenceSpace {
     /// Gets viewer pose represented by this space
-    pub fn get_viewer_pose(&self, base_pose: &WebVRFrameData) -> Transform3D<f64> {
+    pub fn get_viewer_pose(&self, base_pose: &WebVRFrameData) -> RigidTransform3D<f64> {
         let pose = self.get_pose(base_pose);
 
         // This may change, see https://github.com/immersive-web/webxr/issues/567
-        let offset = self.transform.get().matrix();
-        // XXXManishearth we can directly compute the inverse from the transform parameters
-        // (and perhaps cache it)
-        // XXXManishearth we can also optimize for the unset/identity offset case
-        let inverse = offset
-            .inverse()
-            .expect("rigid transforms are always invertible");
+        let offset = self.transform.get().transform();
+        let inverse = offset.inverse();
         inverse.pre_mul(&pose)
     }
 
     /// Gets pose represented by this space
     ///
     /// Does not apply originOffset, use get_viewer_pose instead if you need it
-    pub fn get_pose(&self, base_pose: &WebVRFrameData) -> Transform3D<f64> {
+    pub fn get_pose(&self, base_pose: &WebVRFrameData) -> RigidTransform3D<f64> {
         if let Some(stationary) = self.downcast::<XRStationaryReferenceSpace>() {
             stationary.get_pose(base_pose)
         } else {
             // non-subclassed XRReferenceSpaces exist, obtained via the "identity"
             // type. The pose does not depend on the base pose.
-            Transform3D::identity()
+            RigidTransform3D::identity()
         }
     }
 }