Fix animated model skinning precision issues

#2460

Content/Editor/MaterialTemplates/Surface.shader

@@ -430,7 +430,9 @@ float3x4 GetPrevBoneMatrix(int index)
 float3 SkinPrevPosition(ModelInput_Skinned input)
 {
 	float4 position = float4(input.Position.xyz, 1);
-	float3x4 boneMatrix = input.BlendWeights.x * GetPrevBoneMatrix(input.BlendIndices.x);
+	float weightsSum = input.BlendWeights.x + input.BlendWeights.y + input.BlendWeights.z + input.BlendWeights.w;
+	float mainWeight = input.BlendWeights.x + (1.0f - weightsSum); // Re-normalize to account for 16-bit weights encoding erros
+	float3x4 boneMatrix = mainWeight * GetPrevBoneMatrix(input.BlendIndices.x);
 	boneMatrix += input.BlendWeights.y * GetPrevBoneMatrix(input.BlendIndices.y);
 	boneMatrix += input.BlendWeights.z * GetPrevBoneMatrix(input.BlendIndices.z);
 	boneMatrix += input.BlendWeights.w * GetPrevBoneMatrix(input.BlendIndices.w);
@@ -439,12 +441,6 @@ float3 SkinPrevPosition(ModelInput_Skinned input)
 
 #endif
 
-// Cached skinning data to avoid multiple calculation 
-struct SkinningData
-{
-	float3x4 BlendMatrix;
-};
-
 // Calculates the transposed transform matrix for the given bone index
 float3x4 GetBoneMatrix(int index)
 {
@@ -457,7 +453,9 @@ float3x4 GetBoneMatrix(int index)
 // Calculates the transposed transform matrix for the given vertex (uses blending)
 float3x4 GetBoneMatrix(ModelInput_Skinned input)
 {
-	float3x4 boneMatrix = input.BlendWeights.x * GetBoneMatrix(input.BlendIndices.x);
+	float weightsSum = input.BlendWeights.x + input.BlendWeights.y + input.BlendWeights.z + input.BlendWeights.w;
+	float mainWeight = input.BlendWeights.x + (1.0f - weightsSum); // Re-normalize to account for 16-bit weights encoding erros
+	float3x4 boneMatrix = mainWeight * GetBoneMatrix(input.BlendIndices.x);
 	boneMatrix += input.BlendWeights.y * GetBoneMatrix(input.BlendIndices.y);
 	boneMatrix += input.BlendWeights.z * GetBoneMatrix(input.BlendIndices.z);
 	boneMatrix += input.BlendWeights.w * GetBoneMatrix(input.BlendIndices.w);
@@ -465,13 +463,13 @@ float3x4 GetBoneMatrix(ModelInput_Skinned input)
 }
 
 // Transforms the vertex position by weighted sum of the skinning matrices
-float3 SkinPosition(ModelInput_Skinned input, SkinningData data)
+float3 SkinPosition(ModelInput_Skinned input, float3x4 boneMatrix)
 {
-	return mul(data.BlendMatrix, float4(input.Position.xyz, 1));
+	return mul(boneMatrix, float4(input.Position.xyz, 1));
 }
 
 // Transforms the vertex position by weighted sum of the skinning matrices
-float3x3 SkinTangents(ModelInput_Skinned input, SkinningData data)
+float3x3 SkinTangents(ModelInput_Skinned input, float3x4 boneMatrix)
 {
 	// Unpack vertex tangent frame
 	float bitangentSign = input.Tangent.w ? -1.0f : +1.0f;
@@ -479,10 +477,10 @@ float3x3 SkinTangents(ModelInput_Skinned input, SkinningData data)
 	float3 tangent = input.Tangent.xyz * 2.0 - 1.0;
 
 	// Apply skinning
-	tangent = mul(data.BlendMatrix, float4(tangent, 0));
+	tangent = normalize(mul(boneMatrix, float4(tangent, 0)));
-	normal = mul(data.BlendMatrix, float4(normal, 0));
+	normal = normalize(mul(boneMatrix, float4(normal, 0)));
 
-	float3 bitangent = cross(normal, tangent) * bitangentSign;
+	float3 bitangent = normalize(cross(normal, tangent) * bitangentSign);
 	return float3x3(tangent, bitangent, normal);
 }
 
@@ -501,10 +499,9 @@ VertexOutput VS_Skinned(ModelInput_Skinned input)
 	VertexOutput output;
 	
 	// Perform skinning
-	SkinningData data;
+	float3x4 boneMatrix = GetBoneMatrix(input);
-	data.BlendMatrix = GetBoneMatrix(input);
+	float3 position = SkinPosition(input, boneMatrix);
-	float3 position = SkinPosition(input, data);
+	float3x3 tangentToLocal = SkinTangents(input, boneMatrix);
-	float3x3 tangentToLocal = SkinTangents(input, data);
 	
 	// Compute world space vertex position
 	CalculateInstanceTransform(input);

Source/Engine/Graphics/Materials/MaterialShader.h

@@ -10,7 +10,7 @@
 /// <summary>
 /// Current materials shader version.
 /// </summary>
-#define MATERIAL_GRAPH_VERSION 161
+#define MATERIAL_GRAPH_VERSION 162
 
 class Material;
 class GPUShader;

Source/Engine/Graphics/Models/ModelData.cpp

@@ -563,9 +563,10 @@ void MeshData::NormalizeBlendWeights()
     ASSERT(Positions.Count() == BlendWeights.Count());
     for (int32 i = 0; i < Positions.Count(); i++)
     {
-        const float sum = BlendWeights[i].SumValues();
+        Float4& weights = BlendWeights.Get()[i];
+        const float sum = weights.SumValues();
         const float invSum = sum > ZeroTolerance ? 1.0f / sum : 0.0f;
-        BlendWeights[i] *= invSum;
+        weights *= invSum;
     }
 }
 

Source/Engine/Level/Actors/AnimatedModel.cpp

@@ -113,7 +113,7 @@ void AnimatedModel::PreInitSkinningData()
     for (int32 boneIndex = 0; boneIndex < bonesCount; boneIndex++)
     {
         auto& bone = skeleton.Bones[boneIndex];
-        identityMatrices[boneIndex] = bone.OffsetMatrix * GraphInstance.NodesPose[bone.NodeIndex];
+        identityMatrices.Get()[boneIndex] = bone.OffsetMatrix * GraphInstance.NodesPose[bone.NodeIndex];
     }
     _skinningData.SetData(identityMatrices.Get(), true);
 

Source/Engine/Tools/ModelTool/ModelTool.OpenFBX.cpp

@@ -720,23 +720,23 @@ bool ProcessMesh(ModelData& result, OpenFbxImporterData& data, const ofbx::Mesh*
             {
                 int vtxIndex = clusterIndices[j] - firstVertexOffset;
                 float vtxWeight = (float)clusterWeights[j];
-
                 if (vtxWeight <= 0 || vtxIndex < 0 || vtxIndex >= vertexCount)
                     continue;
-
+                Int4& indices = mesh.BlendIndices.Get()[vtxIndex];
-                auto& indices = mesh.BlendIndices[vtxIndex];
+                Float4& weights = mesh.BlendWeights.Get()[vtxIndex];
-                auto& weights = mesh.BlendWeights[vtxIndex];
 
                 for (int32 k = 0; k < 4; k++)
                 {
                     if (vtxWeight >= weights.Raw[k])
                     {
+                        // Move lower weights by one down
                         for (int32 l = 2; l >= k; l--)
                         {
                             indices.Raw[l + 1] = indices.Raw[l];
                             weights.Raw[l + 1] = weights.Raw[l];
                         }
 
+                        // Set bone influence
                         indices.Raw[k] = boneIndex;
                         weights.Raw[k] = vtxWeight;
                         break;