Fixed cloth tangent generation (#2440)

- The output vectors were not properly filled with zeros when they already had the expected size.
- The tolerance was too large and was causing patches while computing tangents and bitangents.
- The handedness was inverted to what is expected in the shader (which always inverts tangent's w).

Signed-off-by: moraaar <moraaar@amazon.com>

Gems/NvCloth/Code/Source/Components/ClothComponentMesh/ClothComponentMesh.cpp

@@ -577,7 +577,7 @@ namespace NvCloth
                     const AZ::Vector3& renderTangent = renderTangents[renderVertexIndex];
                     destTangentsBuffer[index].Set(
                         renderTangent,
-                        1.0f);
+                        -1.0f); // Shader function ConstructTBN inverts w to change bitangent sign, but the bitangents passed are already corrected, so passing -1.0 to counteract.
                 }
 
                 if (destBitangentsBuffer)

Gems/NvCloth/Code/Source/System/TangentSpaceHelper.cpp

@@ -11,7 +11,7 @@ namespace NvCloth
 {
     namespace
     {
-        const float Tolerance = 0.0001f;
+        const float Tolerance = 1e-7f;
     }
 
     bool TangentSpaceHelper::CalculateNormals(
@@ -33,7 +33,8 @@ namespace NvCloth
         const size_t vertexCount = vertices.size();
 
         // Reset results
-        outNormals.resize(vertexCount, AZ::Vector3::CreateZero());
+        outNormals.resize(vertexCount);
+        AZStd::fill(outNormals.begin(), outNormals.end(), AZ::Vector3::CreateZero());
 
         // calculate the normals per triangle
         for (size_t i = 0; i < triangleCount; ++i)
@@ -114,8 +115,10 @@ namespace NvCloth
         const size_t vertexCount = vertices.size();
 
         // Reset results
-        outTangents.resize(vertexCount, AZ::Vector3::CreateZero());
-        outBitangents.resize(vertexCount, AZ::Vector3::CreateZero());
+        outTangents.resize(vertexCount);
+        outBitangents.resize(vertexCount);
+        AZStd::fill(outTangents.begin(), outTangents.end(), AZ::Vector3::CreateZero());
+        AZStd::fill(outBitangents.begin(), outBitangents.end(), AZ::Vector3::CreateZero());
 
         // calculate the base vectors per triangle
         for (size_t i = 0; i < triangleCount; ++i)
@@ -192,9 +195,12 @@ namespace NvCloth
         const size_t vertexCount = vertices.size();
 
         // Reset results
-        outTangents.resize(vertexCount, AZ::Vector3::CreateZero());
-        outBitangents.resize(vertexCount, AZ::Vector3::CreateZero());
-        outNormals.resize(vertexCount, AZ::Vector3::CreateZero());
+        outTangents.resize(vertexCount);
+        outBitangents.resize(vertexCount);
+        outNormals.resize(vertexCount);
+        AZStd::fill(outTangents.begin(), outTangents.end(), AZ::Vector3::CreateZero());
+        AZStd::fill(outBitangents.begin(), outBitangents.end(), AZ::Vector3::CreateZero());
+        AZStd::fill(outNormals.begin(), outNormals.end(), AZ::Vector3::CreateZero());
 
         // calculate the base vectors per triangle
         for (size_t i = 0; i < triangleCount; ++i)

Gems/NvCloth/Code/Tests/Components/ClothComponentMesh/ClothConstraintsTest.cpp

@@ -124,6 +124,9 @@ namespace UnitTest
         const AZStd::vector<AZ::Vector4>& motionConstraints = clothConstraints->GetMotionConstraints();
 
         EXPECT_TRUE(motionConstraints.size() == SimulationParticles.size());
+        EXPECT_THAT(motionConstraints[0].GetAsVector3(), IsCloseTolerance(SimulationParticles[0].GetAsVector3(), Tolerance));
+        EXPECT_THAT(motionConstraints[1].GetAsVector3(), IsCloseTolerance(SimulationParticles[1].GetAsVector3(), Tolerance));
+        EXPECT_THAT(motionConstraints[2].GetAsVector3(), IsCloseTolerance(SimulationParticles[2].GetAsVector3(), Tolerance));
         EXPECT_NEAR(motionConstraints[0].GetW(), 6.0f, Tolerance);
         EXPECT_NEAR(motionConstraints[1].GetW(), 0.0f, Tolerance);
         EXPECT_NEAR(motionConstraints[2].GetW(), 0.0f, Tolerance);
@@ -277,6 +280,9 @@ namespace UnitTest
         const AZStd::vector<AZ::Vector4>& separationConstraints = clothConstraints->GetSeparationConstraints();
 
         EXPECT_TRUE(motionConstraints.size() == newParticles.size());
+        EXPECT_THAT(motionConstraints[0].GetAsVector3(), IsCloseTolerance(newParticles[0].GetAsVector3(), Tolerance));
+        EXPECT_THAT(motionConstraints[1].GetAsVector3(), IsCloseTolerance(newParticles[1].GetAsVector3(), Tolerance));
+        EXPECT_THAT(motionConstraints[2].GetAsVector3(), IsCloseTolerance(newParticles[2].GetAsVector3(), Tolerance));
         EXPECT_NEAR(motionConstraints[0].GetW(), 3.0f, Tolerance);
         EXPECT_NEAR(motionConstraints[1].GetW(), 1.5f, Tolerance);
         EXPECT_NEAR(motionConstraints[2].GetW(), 0.0f, Tolerance);
@@ -285,8 +291,8 @@ namespace UnitTest
         EXPECT_NEAR(separationConstraints[0].GetW(), 3.0f, Tolerance);
         EXPECT_NEAR(separationConstraints[1].GetW(), 1.5f, Tolerance);
         EXPECT_NEAR(separationConstraints[2].GetW(), 0.3f, Tolerance);
-        EXPECT_THAT(separationConstraints[0].GetAsVector3(), IsCloseTolerance(AZ::Vector3(-3.03902f, 2.80752f, 3.80752f), Tolerance));
-        EXPECT_THAT(separationConstraints[1].GetAsVector3(), IsCloseTolerance(AZ::Vector3(-1.41659f, 0.651243f, -0.348757f), Tolerance));
-        EXPECT_THAT(separationConstraints[2].GetAsVector3(), IsCloseTolerance(AZ::Vector3(6.15313f, -0.876132f, 0.123868f), Tolerance));
+        EXPECT_THAT(separationConstraints[0].GetAsVector3(), IsCloseTolerance(AZ::Vector3(0.0f, 3.53553f, 4.53553f), Tolerance));
+        EXPECT_THAT(separationConstraints[1].GetAsVector3(), IsCloseTolerance(AZ::Vector3(0.0f, 2.06066f, 1.06066f), Tolerance));
+        EXPECT_THAT(separationConstraints[2].GetAsVector3(), IsCloseTolerance(AZ::Vector3(1.0f, -3.74767f, -2.74767f), Tolerance));
     }
 } // namespace UnitTest