Skinning: problem calculating bindpose/offset-matrix

Julian Watzinger · 2014-02-24T09:59:59

Hello, while implementing skinning support to my engine and therefore my mesh file format, I'm down to one problem: The inverse bind pose matrices (at least of my test model) don't match with what would be needed to render it correctly. I've converted the Tiny.x - mesh from the DirectX9-SDK to my own mesh format, and I've verified up until now that all data is 100% matching, minus the bind pose/offset matrix. I am calculating the matrix by traversing the bone hierachy, and then inversing the absolute transform of each bone: void MeshSkeleton::ProcessSkeleton(void) { m_vMatrices.clear(); size_t numBone = 0; ProcessBone(m_root, nullptr, numBone); } void MeshSkeleton::ProcessBone(Bone& bone, Bone* pParent, size_t& numBone) { if(pParent) bone.mAbsolute = bone.mRelative * pParent->mAbsolute; else bone.mAbsolute = bone.mRelative; // in case the inverse bind poses have already been calculated, output the final bone matrix if(!m_vInvBindPoses.empty()) m_vMatrices.push_back(m_vInvBindPoses[numBone] * bone.mAbsolute); else m_vMatrices.push_back(math::MatIdentity()); numBone++; for(auto& child : bone.m_vChildren) { ProcessBone(child, &bone, numBone); } } void MeshSkeleton::CalculateBindPoses(void) { m_vInvBindPoses.clear(); CalculateBindPose(m_root); } void MeshSkeleton::CalculateBindPose(Bone& bone) { m_vInvBindPoses.push_back(bone.mAbsolute.inverse()); for(auto& child : bone.m_vChildren) { CalculateBindPose(child); } } First, ProcessSceleton is called, then CalculateBindPoses. The absolute matrices are identically to those of the Tiny.x-mesh when loaded in the sample, so there should be no problem here. However, when I look at the offset matrices from the sample: // get each of the bone offset matrices so that we don't need to get them later for( iBone = 0; iBone < cBones; iBone++ ) { pMeshContainer->pBoneOffsetMatrices[iBone] = *( pMeshContainer->pSkinInfo->GetBoneOffsetMatrix( iBone ) ); } They aren't even similiar to mine in any way shape or form (I checked the correct bones). Now I can fix this by storing the offset matrix from pSkinInfo in the mesh file and load them with the file (that way the animation works correctly), but I am wondering about the reasoning behind this. Is there some error in my calculations? Or is the offset-matrix calculated differently in the DirectX9-file format?