From 6c5963ad6b4541f5fa0812607fd36a979c48c0f1 Mon Sep 17 00:00:00 2001
From: Alexander Cooper <[email protected]>
Date: Thu, 16 Oct 2025 10:54:37 -0700
Subject: [PATCH] [WebXR] Update detached matrix handling

Updates a few places that handle an array representation of a matrix
being detached by returning a 0-length array to simply recompute the
array that should be present, based on the presence of other data. This
more closely matches the spec, which for both of these cases essentially
state that if the value is not null to check if it's detached, and if it
is not detached to return the value. The steps following both of these
checks then recompute the matrix, so technically our current impl is
not spec-compliant to that.

Further, we remove one unused array to transform conversion helper and
update another to a CHECK from a DCHECK to match best practices for
invariants.

Fixed: 452071845
Change-Id: Idf765fe5717d59ae63c71e8253784ff4473dea5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7046576
Commit-Queue: Alexander Cooper <[email protected]>
Reviewed-by: Brandon Jones <[email protected]>
Auto-Submit: Alexander Cooper <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1530947}
---

diff --git a/third_party/blink/renderer/modules/xr/xr_rigid_transform.cc b/third_party/blink/renderer/modules/xr/xr_rigid_transform.cc
index 68afd463..d0a8cc6 100644
--- a/third_party/blink/renderer/modules/xr/xr_rigid_transform.cc
+++ b/third_party/blink/renderer/modules/xr/xr_rigid_transform.cc
@@ -108,15 +108,8 @@
 
 NotShared<DOMFloat32Array> XRRigidTransform::matrix() {
   EnsureMatrix();
-  if (!matrix_array_) {
-    matrix_array_ = transformationMatrixToDOMFloat32Array(*matrix_);
-  }
-
   if (!matrix_array_ || matrix_array_->IsDetached()) {
-    // A page may take the matrix_array_ value and detach it so matrix_array_ is
-    // a detached array buffer.  This breaks the inspector, so return an empty
-    // array instead.
-    return NotShared<DOMFloat32Array>(DOMFloat32Array::Create(0));
+    matrix_array_ = transformationMatrixToDOMFloat32Array(*matrix_);
   }
 
   return matrix_array_;
diff --git a/third_party/blink/renderer/modules/xr/xr_utils.cc b/third_party/blink/renderer/modules/xr/xr_utils.cc
index 55188dd..307b902 100644
--- a/third_party/blink/renderer/modules/xr/xr_utils.cc
+++ b/third_party/blink/renderer/modules/xr/xr_utils.cc
@@ -23,15 +23,10 @@
 }
 
 gfx::Transform DOMFloat32ArrayToTransform(NotShared<DOMFloat32Array> m) {
-  DCHECK_EQ(m->length(), 16u);
+  CHECK_EQ(m->length(), 16u);
   return gfx::Transform::ColMajorF(m->Data());
 }
 
-gfx::Transform WTFFloatVectorToTransform(const Vector<float>& m) {
-  DCHECK_EQ(m.size(), 16u);
-  return gfx::Transform::ColMajorF(m.data());
-}
-
 // Normalize to have length = 1.0
 DOMPointReadOnly* makeNormalizedQuaternion(double x,
                                            double y,
diff --git a/third_party/blink/renderer/modules/xr/xr_utils.h b/third_party/blink/renderer/modules/xr/xr_utils.h
index 87b93d8..f61aa18d6 100644
--- a/third_party/blink/renderer/modules/xr/xr_utils.h
+++ b/third_party/blink/renderer/modules/xr/xr_utils.h
@@ -31,8 +31,6 @@
 
 gfx::Transform DOMFloat32ArrayToTransform(NotShared<DOMFloat32Array>);
 
-gfx::Transform WTFFloatVectorToTransform(const Vector<float>&);
-
 DOMPointReadOnly* makeNormalizedQuaternion(double x,
                                            double y,
                                            double z,
diff --git a/third_party/blink/renderer/modules/xr/xr_view.cc b/third_party/blink/renderer/modules/xr/xr_view.cc
index af482ed..dcd02ac 100644
--- a/third_party/blink/renderer/modules/xr/xr_view.cc
+++ b/third_party/blink/renderer/modules/xr/xr_view.cc
@@ -81,7 +81,8 @@
     // A page may take the projection matrix value and detach it so
     // projection_matrix_ is a detached array buffer.  This breaks the
     // inspector, so return an empty array instead.
-    return NotShared<DOMFloat32Array>(DOMFloat32Array::Create(0));
+    projection_matrix_ =
+        transformationMatrixToDOMFloat32Array(view_data_->ProjectionMatrix());
   }
 
   return projection_matrix_;
diff --git a/third_party/blink/renderer/modules/xr/xr_view.h b/third_party/blink/renderer/modules/xr/xr_view.h
index f90f85a5..549c0895 100644
--- a/third_party/blink/renderer/modules/xr/xr_view.h
+++ b/third_party/blink/renderer/modules/xr/xr_view.h
@@ -74,7 +74,10 @@
   // The transform from the view to the reference space requested by
   // XRFrame::getViewerPose.
   Member<XRRigidTransform> ref_space_from_view_;
-  NotShared<DOMFloat32Array> projection_matrix_;
+  // This is just a cached/converted version of the projection matrix from the
+  // view_data. It's mutable so that we can update it when queried if it was
+  // detached.
+  mutable NotShared<DOMFloat32Array> projection_matrix_;
   Member<XRViewport> viewport_;
 };