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We’re having some problems getting our skinned mesh animation to work correctly when converting an FBX to our own format. Whenever animation is applied, the model seems to rotate 90 degrees about the X axis. I’m sure it has to be something to do with either the PreRotation or the coordinate system conversion, but I’m not sure exactly what. The steps we go through are:
The FBX is saved out with Y-Up from 3DS Max. It contains a mesh which is skinned using CAT.
Each node has its original transformation stored as Translation, Rotation Quaternion and Scale, using the following code:
KTime kTime;
kTime.SetSecondDouble(0);
FbxAMatrix Transform = Node->EvaluateLocalTransform(kTime);
FbxVector4 Translation = Transform.GetT();
FbxQuaternion QuatRotation = Transform.GetQ();
FbxVector4 Angles = Transform.GetR();
FbxVector4 Scale = Transform.GetS();
NewNode->Translation[0] = Translation[0];
NewNode->Translation[1] = Translation[1];
NewNode->Translation[2] = Translation[2];
NewNode->Rotation[0] = QuatRotation[0];
NewNode->Rotation[1] = QuatRotation[1];
NewNode->Rotation[2] = QuatRotation[2];
NewNode->Rotation[3] = QuatRotation[3];
NewNode->Scale[0] = Scale[0];
NewNode->Scale[1] = Scale[1];
NewNode->Scale[2] = Scale[2];
So the transformations for each node are stored relative to the parent.
When evaluating the transformations for each node for the animations, we do the following:
// Evaluate the node at the given time
KTime kTime;
kTime.SetSecondDouble(Time);
FbxAMatrix Transform = m_pFBXNode->EvaluateLocalTransform(kTime);
FbxVector4 Translation = Transform.GetT();
FbxQuaternion QuatRotation = Transform.GetQ();
FbxVector4 Scale = Transform.GetS();
// Make the values relative to time of 0
kTime.SetSecondDouble(0);
FbxAMatrix Frame0Transform = m_pFBXNode->EvaluateLocalTransform(kTime);
FbxVector4 Frame0Translation = Frame0Transform.GetT();
FbxQuaternion Frame0QuatRotation = Frame0Transform.GetQ();
FbxVector4 Frame0Scale = Frame0Transform.GetS();
FbxAMatrix InverseFrame0Transform = Frame0Transform.Inverse();
FbxAMatrix RelativeTransform = InverseFrame0Transform * Transform;
Translation = RelativeTransform.GetT();
QuatRotation = RelativeTransform.GetQ();
Scale = Transform.GetS() - Frame0Scale;
Keyframe[0] = (float)Translation[0];
Keyframe[1] = (float)Translation[1];
Keyframe[2] = (float)Translation[2];
Keyframe[3] = (float)QuatRotation[0];
Keyframe[4] = (float)QuatRotation[1];
Keyframe[5] = (float)QuatRotation[2];
Keyframe[6] = (float)QuatRotation[3];
Keyframe[7] = (float)Scale[0];
Keyframe[8] = (float)Scale[1];
Keyframe[9] = (float)Scale[2];
This gets us the relative transformation from the frame 0 one. We do this so we can use additive blending on multiple animations.
We also store the inverse bind pose matrices for the bones as follows:
// Store the inverse bind pose matrix
FbxAMatrix globalMatrix;
Cluster->GetTransformMatrix(globalMatrix);
const FbxVector4 GeomTranslation = Mesh->GetNode()->GetGeometricTranslation(FbxNode::eSourcePivot);
const FbxVector4 GeomRotation = Mesh->GetNode()->GetGeometricRotation(FbxNode::eSourcePivot);
const FbxVector4 GeomScaling = Mesh->GetNode()->GetGeometricScaling(FbxNode::eSourcePivot);
FbxAMatrix geomMatrix = FbxAMatrix(GeomTranslation, GeomRotation, GeomScaling);
globalMatrix *= geomMatrix;
FbxAMatrix bindPoseMatrix;
Cluster->GetTransformLinkMatrix(bindPoseMatrix);
bindPoseMatrix = bindPoseMatrix.Inverse() * globalMatrix;
// We need to transpose the matrix to get it into engine format
FbxMatrix tempMatrix(bindPoseMatrix);
FbxMatrix transposedBindPoseMatrix = tempMatrix.Transpose();
double* bindPoseMatrixData = (double*)transposedBindPoseMatrix;
array<float>^ invBindPoseMatrix = gcnew array<float>(16);
for(int arrayIndex = 0; arrayIndex < 16; ++arrayIndex)
{
invBindPoseMatrix[arrayIndex] = (float)bindPoseMatrixData[arrayIndex];
}
NewBoneData->SetInvBindPoseMatrix(invBindPoseMatrix);
Then when we are rendering, we calculate the skinning matrices like so:
// Get the transformation for the bone
const MathsNS::Matrix4x4& boneTransform = pNodeInstance->GetTransform();
// Get the inverse transform for the original bone node
const MathsNS::Matrix4x4& invBoneTransform = CurrentMesh->m_BoneInvBindPoseMatrices[boneIndex];
// Set the shader parameter for this bone
boneMatrices.push_back(boneTransform * invBoneTransform);
Like I mentioned, the whole thing seems to work fine, and animates OK, but the mesh is rotated 90 degrees on the X axis. If we replace the last line with:
boneMatrices.push_back(Matrix4x4::Identity);
The mesh faces the correct way, so my thinking is that the inverse bind pose matrices and everything are OK, but the animation transformations or maybe the default pose transformations are not retrieved properly. When rendering, all mesh / bone node transformations are calculated by constructing the matrix from the transforms retrieved in the first code segment and multiplying by the relative transformation matrices constructed from the data in the second code segment.
Does anyone have any idea what we’re doing wrong, or why we might be seeing this 90 degree rotation? I thought using EvaluateLocalTransform was supposed to take all of the Pre/Post rotation stuff into consideration. Maybe there’s a step we’ve missed or something?
Thanks
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