[VFX][Fix 1400636] XR & World Space Motion Vector incorrect (#313)

* put vertPosWorld into camera relative WS

* fix warning + changelog

Author: ludovic-theobald

com.unity.visualeffectgraph/CHANGELOG.md

@@ -36,6 +36,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - In `Output Particle` blocks, shader graph exposed properties order is consistent with shader graph blackboard
 - Picking and Selection passes [Case 1382788](https://issuetracker.unity3d.com/product/unity/issues/guid/1382788/), [Case 1402283](https://issuetracker.unity3d.com/product/unity/issues/guid/1402283/)
 - Reduce GC.Allocs in the SceneViewGUICallback. [Case 1305929](https://issuetracker.unity3d.com/product/unity/issues/guid/1305929/)
+- Fix Motion vectors in XR. [Case 14003636](https://issuetracker.unity3d.com/product/unity/issues/guid/14003636/)
 
 ## [14.0.0] - 2021-11-17
 

com.unity.visualeffectgraph/Shaders/VFXOutputUpdate.template

@@ -219,6 +219,7 @@ ${VFXFeedSortingKeys}
                     for (int itIndexVert = 0; itIndexVert < VFX_FEATURE_MOTION_VECTORS_VERTS; ++itIndexVert)
                     {
                         float4 vertPosWorld = float4(TransformPositionVFXToWorld(verts[itIndexVert]), 1.0f);
+                        vertPosWorld.xyz = VFXTransformPositionWorldToCameraRelative(vertPosWorld.xyz);
                         float4 vertPosA = mul(_XRNonJitteredViewProjMatrix[0], vertPosWorld);
                         float4 vertPosB = mul(_XRNonJitteredViewProjMatrix[1], vertPosWorld + stereoOffset);
                         elementToVFXBuffer.Store4(elementToVFXIndex << 2, asuint(float4(vertPosA.xy / vertPosA.w, vertPosB.xy / vertPosB.w)));