Auto merge of #23169 - Manishearth:more-pose, r=jdm

Some more pose fixes

Based on https://github.com/servo/servo/pull/23164

This:

 - Adds support for position-disabled
 - Adds approximate support for floor-level
 - Makes transform.inverse.inverse return the original transform
(https://github.com/immersive-web/webxr/issues/576)

To support floor-level *properly* we have to decompose the `sitting_to_standing_transform` matrix. I'll have to add decomposition to euclid to do this, sadly.

It may be possible to reuse the decomposition code in servo's style crate, but there's a chance that that's written with column vector style, given that it reflects the CSS transforms spec, which is also written in column vector style. Ugh.

r? @asajeffrey

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components/script/dom/xrreferencespace.rs

@@ -56,12 +56,18 @@ impl XRReferenceSpaceMethods for XRReferenceSpace {
 impl XRReferenceSpace {
     /// Gets pose of the viewer with respect to this space
     ///
-    /// This is equivalent to `get_pose(self).inverse() * get_pose(viewerSpace)`, however
-    /// we specialize it to be efficient
+    /// This is equivalent to `get_pose(self).inverse() * get_pose(viewerSpace)` (in column vector notation),
+    /// however we specialize it to be efficient
     pub fn get_viewer_pose(&self, base_pose: &WebVRFrameData) -> RigidTransform3D<f64> {
         let pose = self.get_unoffset_viewer_pose(base_pose);
 
         // This may change, see https://github.com/immersive-web/webxr/issues/567
+
+        // in column-vector notation,
+        // get_viewer_pose(space) = get_pose(space).inverse() * get_pose(viewer_space)
+        //                        = (get_unoffset_pose(space) * offset).inverse() * get_pose(viewer_space)
+        //                        = offset.inverse() * get_unoffset_pose(space).inverse() * get_pose(viewer_space)
+        //                        = offset.inverse() * get_unoffset_viewer_pose(space)
         let offset = self.transform.get().transform();
         let inverse = offset.inverse();
         inverse.pre_mul(&pose)

components/script/dom/xrrigidtransform.rs

@@ -100,8 +100,11 @@ impl XRRigidTransformMethods for XRRigidTransform {
     }
     // https://immersive-web.github.io/webxr/#dom-xrrigidtransform-inverse
     fn Inverse(&self) -> DomRoot<XRRigidTransform> {
-        self.inverse
-            .or_init(|| XRRigidTransform::new(&self.global(), self.transform.inverse()))
+        self.inverse.or_init(|| {
+            let transform = XRRigidTransform::new(&self.global(), self.transform.inverse());
+            transform.inverse.set(Some(self));
+            transform
+        })
     }
     // https://immersive-web.github.io/webxr/#dom-xrrigidtransform-matrix
     #[allow(unsafe_code)]

components/script/dom/xrstationaryreferencespace.rs

@@ -12,7 +12,7 @@ use crate::dom::xrrigidtransform::XRRigidTransform;
 use crate::dom::xrsession::XRSession;
 use crate::dom::xrspace::XRSpace;
 use dom_struct::dom_struct;
-use euclid::RigidTransform3D;
+use euclid::{RigidTransform3D, Vector3D};
 use webvr_traits::WebVRFrameData;
 
 #[dom_struct]
@@ -54,19 +54,68 @@ impl XRStationaryReferenceSpace {
     /// Gets pose of the viewer with respect to this space
     ///
     /// Does not apply originOffset, use get_viewer_pose on XRReferenceSpace instead
-    pub fn get_unoffset_viewer_pose(&self, base_pose: &WebVRFrameData) -> RigidTransform3D<f64> {
-        // XXXManishearth add floor-level transform for floor-level and disable position in position-disabled
-        XRSpace::viewer_pose_from_frame_data(base_pose)
+    pub fn get_unoffset_viewer_pose(&self, viewer_pose: &WebVRFrameData) -> RigidTransform3D<f64> {
+        let viewer_pose = XRSpace::viewer_pose_from_frame_data(viewer_pose);
+        // all math is in column-vector notation
+        // we use the following equation to verify correctness here:
+        // get_viewer_pose(space) = get_pose(space).inverse() * get_pose(viewer_space)
+        match self.ty {
+            XRStationaryReferenceSpaceSubtype::Eye_level => {
+                // get_viewer_pose(eye_level) = get_pose(eye_level).inverse() * get_pose(viewer_space)
+                //                            = I * viewer_pose
+                //                            = viewer_pose
+
+                // we get viewer poses in eye-level space by default
+                viewer_pose
+            },
+            XRStationaryReferenceSpaceSubtype::Floor_level => {
+                // XXXManishearth support getting floor info from stage parameters
+
+                // get_viewer_pose(floor_level) = get_pose(floor_level).inverse() * get_pose(viewer_space)
+                //                            = Translate(-2).inverse() * viewer_pose
+                //                            = Translate(2) * viewer_pose
+
+                // assume approximate user height of 2 meters
+                let floor_to_eye: RigidTransform3D<f64> = Vector3D::new(0., 2., 0.).into();
+                floor_to_eye.pre_mul(&viewer_pose)
+            },
+            XRStationaryReferenceSpaceSubtype::Position_disabled => {
+                // get_viewer_pose(pos_disabled) = get_pose(pos_disabled).inverse() * get_pose(viewer_space)
+                //                            = viewer_pose.translation.inverse() * viewer_pose
+                //                            = viewer_pose.translation.inverse() * viewer_pose.translation
+                //                                                                * viewer_pose.rotation
+                //                            = viewer_pose.rotation
+
+                // This space follows the user around, but does not mirror the user's orientation
+                // Thus, the viewer's pose relative to this space is simply their orientation
+                viewer_pose.rotation.into()
+            },
+        }
     }
 
     /// Gets pose represented by this space
     ///
     /// Does not apply originOffset, use get_pose on XRReferenceSpace instead
-    pub fn get_unoffset_pose(&self, _: &WebVRFrameData) -> RigidTransform3D<f64> {
+    pub fn get_unoffset_pose(&self, viewer_pose: &WebVRFrameData) -> RigidTransform3D<f64> {
         // XXXManishearth add floor-level transform for floor-level and disable position in position-disabled
-
+        match self.ty {
+            XRStationaryReferenceSpaceSubtype::Eye_level => {
                 // The eye-level pose is basically whatever the headset pose was at t=0, which
                 // for most devices is (0, 0, 0)
                 RigidTransform3D::identity()
+            },
+            XRStationaryReferenceSpaceSubtype::Floor_level => {
+                // XXXManishearth support getting floor info from stage parameters
+
+                // Assume approximate height of 2m
+                // the floor-level space is 2m below the eye-level space, which is (0, 0, 0)
+                Vector3D::new(0., -2., 0.).into()
+            },
+            XRStationaryReferenceSpaceSubtype::Position_disabled => {
+                // This space follows the user around, but does not mirror the user's orientation
+                let viewer_pose = XRSpace::viewer_pose_from_frame_data(viewer_pose);
+                viewer_pose.translation.into()
+            },
+        }
     }
 }