Fix mirror skybox reflection matrices (#1009)

## Summary
* Skybox reflection was not correct in the basis mirror which caused
weird rotation offset from user perspective.

## Required checks
All boxes below must be ticked before this PR can merge. If a check is
genuinely N/A, tick it anyway and explain under **Notes**.

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- [x] **Tested** — I built and ran this locally. The change works in the
editor and (where relevant) in a built player.
- [x] **Transform access is combined and limited** — In hot paths,
transform reads/writes go through `TransformAccessArray` or are
otherwise batched. I have not added per-frame `transform.position` /
`transform.rotation` / `transform.localPosition` calls inside loops.
Whenever I need both position and rotation, I use the combined APIs —
`SetPositionAndRotation` / `SetLocalPositionAndRotation` for writes,
`GetPositionAndRotation` / `GetLocalPositionAndRotation` for reads —
instead of two separate property accesses; the combined call does one
local-to-world matrix traversal instead of two.
- [x] **Addressables used for asset/memory loading** — Any new asset
loads go through Addressables. No new `Resources.Load`, no direct asset
references that pull large content into memory on scene load.
- [x] **No new `GetComponent` / `AddComponent` where avoidable** — Where
unavoidable, the result is cached on a field, and any `GetComponent<T>`
is replaced with `TryGetComponent<T>(out var x)` — bare `GetComponent`
will be denied. `TryGetComponent` is the modern API (Unity 2019.2+) and
skips the Editor-only GC allocation `GetComponent` causes when a
component is missing: Unity wraps the `null` return in a managed "fake
null" object so its overloaded `==` operator can still detect destroyed
C++ objects, and constructing that wrapper allocates; `TryGetComponent`
returns a `bool` plus `out` parameter and never builds the wrapper. None
of these calls run inside `Update`, `LateUpdate`, `FixedUpdate`, jobs,
or other per-frame code paths.
- [x] **Per-frame work is scheduled through `BasisEventDriver`** — Any
new per-frame work hooks into `BasisEventDriver` rather than adding
standalone `Update` / `LateUpdate` / `FixedUpdate` callbacks on a
MonoBehaviour.
- [x] **Anything added to `BasisEventDriver` is bulletproof, or guarded
by `try`/`catch`** — `BasisEventDriver` runs the single per-frame tick
that drives the whole framework (network apply, local player sim,
blendshapes, JigglePhysics, nameplates, and more) as one sequential
chain. An unhandled exception anywhere in that chain aborts the rest of
the tick, so every step after the throwing one is silently skipped for
that frame. New work added to the driver must either be guaranteed not
to throw, or be wrapped in a `try`/`catch` that contains the failure and
surfaces it through `BasisDebug` — logged once / rate-limited, never
every frame (see the existing `HVRBasisBuiltInAddresses.Simulate()`
guard for the pattern). Expect this to be scrutinized closely in review.
- [x] **Considered jobification** — I asked whether this work can be
moved to a Unity Job (Burst-compiled where possible). If it can, it is.
If it cannot, the reason is in **Notes**.
- [x] **No needless `{ get; set; }` properties or access lockdowns** —
Public fields are fine; Basis is meant to be read and modified freely,
so don't wall things off `private`/`internal` without a real reason.
Don't wrap a field in `{ get; set; }` when the accessors do nothing —
property accessors have a real performance cost vs direct field access,
and the lead maintainer prefers plain fields (or a method / setter-only
property when only the setter needs logic) over a noop-getter pair. For
`.Instance` singletons, callers reassigning `Type.Instance` is allowed;
if that would break your code, log a warning or throw — don't block the
assignment. Locking down access is not your call.
- [x] **Camera access goes through `BasisLocalCameraDriver`** — Code
that needs the local camera (transform, projection, rig data, etc.)
pulls it from `BasisLocalCameraDriver` rather than looking one up
itself. Don't roll a separate camera discovery path.
- [x] **Logging uses `BasisDebug`** — All new logging calls go through
`BasisDebug.Log` / `BasisDebug.LogWarning` / `BasisDebug.LogError` (with
an appropriate `LogTag`) instead of `UnityEngine.Debug.Log` /
`Debug.LogWarning` / `Debug.LogError`. `BasisDebug` routes through
Basis's tagged, color-coded logger and respects the project-wide
`LoggingDisabled` toggle so logging can be killed at runtime; bare
`Debug.Log` calls bypass that and will be denied.
- [x] **No scene-wide discovery for dependencies** — New code is
architected so it does not need `FindObjectOfType` / `FindObjectsOfType`
/ `GameObject.Find` / `FindGameObjectsWithTag` to locate what it depends
on. References are wired in — registered through an existing
manager/driver, injected at init, or passed in by the caller — rather
than discovered by scanning the scene at runtime. If a scene scan is
genuinely unavoidable, justify it under **Notes**.
- [x] **No allocations in hot paths** — Per-frame code (Update /
LateUpdate / FixedUpdate, simulation loops, jobs, anything called once
per frame or more) does not allocate. No `new` on reference types, no
LINQ, no `string` concatenation/interpolation, no boxing, no `foreach`
over interface-typed collections. Allocate once at init and reuse the
buffer.
- [x] **No debugging in hot paths** — No log calls of any kind on
per-frame paths, including `BasisDebug`. Hot-path logging floods the
console and incurs cost on every frame regardless of whether the message
is filtered out downstream. If a hot-path log is needed while iterating,
gate it behind `#if UNITY_EDITOR` and remove (or leave gated) before
merge.
- [x] **Hot-path collection access is optimized** — Cache `.Count`
(lists) / `.Length` (arrays) into a local `int` before the loop instead
of re-reading the property each iteration. Prefer `T[]` (with a separate
length int when the array is over-sized) over `List<T>` where the data
is hot — Unity's mono BCL doesn't expose
`CollectionsMarshal.AsSpan(List<T>)`, so a list can't be fed into
`Span<T>` / unsafe paths cleanly. Where the perf justifies it, drop into
`Span<T>` / `ref` locals / `Unsafe.As` / `unsafe` pointer code to skip
bounds checks and copies, and call out the invariants you're relying on
under **Notes** so reviewers can sanity-check them.
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## Testing details
Tick the platforms you actually tested on. Leave the rest unticked —
these are informational and do not block merge.

- [x] Windows
- [ ] Linux
- [ ] Android
- [ ] iOS
- [ ] macOS

Input / control mode coverage:

- [x] Tested in VR (note headset under **Notes**)
- [x] Tested in desktop / non-VR mode
- [ ] Tested with phone controls (mobile touch input)
- [ ] N/A — change does not touch player/XR/input code

Where applicable, confirm these flows still work after your changes:

- [ ] Hot-switching (desktop ↔ VR mode swap at runtime)
- [ ] Avatar swapping
- [ ] Server swapping (joining / leaving / changing servers)
- [ ] N/A — change does not touch any of the above

## Notes
<!-- Optional context for reviewers. Headset model, why a required box
is N/A, anything else worth knowing. -->

Author: dooly123

Basis/Packages/com.basis.examples/Scripts/BasisSDKMirror.cs

@@ -1020,6 +1020,11 @@ private void RenderEye(Camera sourceCamera, MonoOrStereoscopicEye eye, Vector3 s
         // steep view angles and wrongly cull renderers that are actually visible in the mirror.
         portalCamera.cullingMatrix = xFlip * proj * xFlip * worldToCam;
 
+        // Skyboxes are infinitely distant and must not receive the mirror-plane oblique clip.
+        // Preserve the clean reflected projection so URP can render the skybox with the same
+        // reflected view as geometry but without the clip-plane distortion.
+        portalCamera.nonJitteredProjectionMatrix = xFlip * proj * xFlip;
+
         // Oblique clip to avoid "behind mirror"; clip normal chosen toward the eye.
         Vector3 clipNormal = planeNormal * Mathf.Sign(Vector3.Dot(eyeOriginWS - planePosWS, planeNormal));
         Vector4 clipPlaneCamSpace = BasisHelpers.CameraSpacePlane(
@@ -1193,6 +1198,7 @@ private void CreateNewCamera(Camera sourceCamera, out Camera newCamera, out Univ
         updateCameraClearFlags(newCamera, sourceCamera);
 
         cameraData = newCamera.GetUniversalAdditionalCameraData();
+        cameraData.isMirrorReflectionCamera = true;
         ApplyCameraOptions(newCamera, cameraData);
 
         if (cameraData != null)

Basis/Packages/com.unity.render-pipelines.universal/Runtime/FrameData/UniversalCameraData.cs

@@ -254,6 +254,7 @@ internal Matrix4x4 GetGPUProjectionMatrix(bool renderIntoTexture, int viewIndex
         /// Returns true if XR rendering is enabled.
         /// </summary>
         public bool xrRendering;
+        internal bool isMirrorReflectionCamera;
 
         // True if GPU occlusion culling should be used when rendering this camera.
         internal bool useGPUOcclusionCulling;
@@ -653,6 +654,7 @@ public override void Reset()
             requiresOpaqueTexture = false;
             postProcessingRequiresDepthTexture = false;
             xrRendering = false;
+            isMirrorReflectionCamera = false;
             useGPUOcclusionCulling = false;
             defaultOpaqueSortFlags = SortingCriteria.None;
             xr = default;

Basis/Packages/com.unity.render-pipelines.universal/Runtime/Passes/DrawSkyboxPass.cs

@@ -45,7 +45,21 @@ private RendererListHandle CreateSkyBoxRendererList(RenderGraph renderGraph, Uni
             else
 #endif
             {
-                skyRendererListHandle = renderGraph.CreateSkyboxRendererList(cameraData.camera);
+                // Mirror reflection cameras use a custom reflected view and an oblique projection
+                // for scene geometry. The native camera-only skybox path does not preserve that setup
+                // correctly, and the oblique clip must not be applied to an infinitely distant skybox.
+                // Basis mirrors store their clean pre-oblique projection in nonJitteredProjectionMatrix.
+                if (cameraData.isMirrorReflectionCamera)
+                {
+                    skyRendererListHandle = renderGraph.CreateSkyboxRendererList(
+                        cameraData.camera,
+                        cameraData.camera.nonJitteredProjectionMatrix,
+                        cameraData.GetViewMatrix(0));
+                }
+                else
+                {
+                    skyRendererListHandle = renderGraph.CreateSkyboxRendererList(cameraData.camera);
+                }
             }
 
             return skyRendererListHandle;

Basis/Packages/com.unity.render-pipelines.universal/Runtime/UniversalAdditionalCameraData.cs

@@ -477,6 +477,7 @@ public partial class UniversalAdditionalCameraData : MonoBehaviour, ISerializati
         [SerializeField] Vector4 m_ScreenCoordScaleBias;
 
         [NonSerialized] Camera m_Camera;
+        [NonSerialized] public bool isMirrorReflectionCamera;
         // Deprecated:
         [FormerlySerializedAs("requiresDepthTexture"), SerializeField]
         bool m_RequiresDepthTexture = false;
@@ -525,7 +526,6 @@ void Start()
                 camera.clearFlags = CameraClearFlags.Nothing;
         }
 
-
         /// <summary>
         /// Controls if this camera should render shadows.
         /// </summary>

Basis/Packages/com.unity.render-pipelines.universal/Runtime/UniversalRenderPipeline.cs

@@ -1699,6 +1699,7 @@ static void InitializeAdditionalCameraData(Camera camera, UniversalAdditionalCam
             bool anyShadowsEnabled = settings.supportsMainLightShadows || settings.supportsAdditionalLightShadows;
             cameraData.maxShadowDistance = Mathf.Min(settings.shadowDistance, camera.farClipPlane);
             cameraData.maxShadowDistance = (anyShadowsEnabled && cameraData.maxShadowDistance >= camera.nearClipPlane) ? cameraData.maxShadowDistance : 0.0f;
+            cameraData.isMirrorReflectionCamera = additionalCameraData != null && additionalCameraData.isMirrorReflectionCamera;
 
             bool isSceneViewCamera = cameraData.isSceneViewCamera;
             if (isSceneViewCamera)