HnSkinningComputation: added GetLastFrameXforms() method

Author: TheMostDiligent

Hydrogent/include/Computations/HnSkinningComputation.hpp

@@ -59,6 +59,7 @@ class HnSkinningComputation final : public HnExtComputationImpl
     static bool IsCompatible(const HnExtComputation& Owner);
 
     const pxr::VtMatrix4fArray& GetXforms() const { return m_Xforms[m_CurrXformsIdx]; }
+    const pxr::VtMatrix4fArray& GetLastFrameXforms() const { return m_Xforms[1 - m_CurrXformsIdx]; }
     size_t                      GetXformsHash() const { return m_XformsHash; }
 
     const float4x4& GetPrimWorldToLocal() const { return m_PrimWorldToLocal; }

Hydrogent/interface/HnMesh.hpp

@@ -112,9 +112,10 @@ class HnMesh final : public pxr::HdMesh
 
         struct Skinning
         {
-            const pxr::VtMatrix4fArray* Xforms        = nullptr;
-            size_t                      XformsHash    = 0;
-            float4x4                    GeomBindXform = float4x4::Identity();
+            const pxr::VtMatrix4fArray* Xforms          = nullptr;
+            const pxr::VtMatrix4fArray* LastFrameXforms = nullptr;
+            size_t                      XformsHash      = 0;
+            float4x4                    GeomBindXform   = float4x4::Identity();
 
             explicit operator bool() const { return Xforms != nullptr; }
         };

Hydrogent/src/Computations/HnSkinningComputation.cpp

@@ -74,10 +74,15 @@ void HnSkinningComputation::Sync(pxr::HdSceneDelegate* SceneDelegate,
             pxr::VtValue SkinningXformsVal = SceneDelegate->GetExtComputationInput(Id, HnSkinningComputationPrivateTokens->skinningXforms);
             if (SkinningXformsVal.IsHolding<pxr::VtMatrix4fArray>())
             {
-                m_CurrXformsIdx              = (m_CurrXformsIdx + 1) % m_Xforms.size();
+                pxr::VtMatrix4fArray& LastXforms = m_Xforms[m_CurrXformsIdx];
+                VERIFY_EXPR(m_Xforms.size() == 2);
+                m_CurrXformsIdx              = 1 - m_CurrXformsIdx;
                 pxr::VtMatrix4fArray& Xforms = m_Xforms[m_CurrXformsIdx];
 
-                Xforms       = SkinningXformsVal.UncheckedGet<pxr::VtMatrix4fArray>();
+                Xforms = SkinningXformsVal.UncheckedGet<pxr::VtMatrix4fArray>();
+                if (LastXforms.empty())
+                    LastXforms = Xforms;
+
                 m_XformsHash = pxr::TfHash{}(Xforms);
 
                 const HnRenderDelegate* RenderDelegate = static_cast<const HnRenderDelegate*>(SceneDelegate->GetRenderIndex().GetRenderDelegate());

Hydrogent/src/HnMesh.cpp

@@ -915,8 +915,9 @@ void HnMesh::UpdateSkinningPrimvars(pxr::HdSceneDelegate&
 
     if (const HnSkinningComputation* SkinningCompImpl = SkinningComp->GetImpl<HnSkinningComputation>())
     {
-        SkinningData.Xforms     = &SkinningCompImpl->GetXforms();
-        SkinningData.XformsHash = SkinningCompImpl->GetXformsHash();
+        SkinningData.Xforms          = &SkinningCompImpl->GetXforms();
+        SkinningData.LastFrameXforms = &SkinningCompImpl->GetLastFrameXforms();
+        SkinningData.XformsHash      = SkinningCompImpl->GetXformsHash();
 
         const float4x4& SkelLocalToPrimLocal = SkinningCompImpl->GetSkelLocalToPrimLocal();
         if (SkelLocalToPrimLocal != m_SkelLocalToPrimLocal)