Broken animation in OpenGL using ASSIMP

Question

Working on a small project, currently trying to implement animation. Like most beginners I am simply following tutorials, this one being the LearnOpenGL Skeletal. All code for Bone/Animation/Animator is taken from that and implemented with my existing structure.

I get an issue where I load the model (From Mixamo, exported in Blender as a .gltf, and imported via assimp) where only some of the model is animating.

Has anyone encountered this issue before? My assumption would by my Shader or my BoneInfoMaps I am generating from ASSIMP are incorrect, but I can see what appears to be a correct amount of bones being created & Offsets applied:

Each aiMesh has these run against it:

void Model::SetVertexBoneData(Vertex& vertex, int boneID, float weight){
for (int i = 0; i < MAX_BONE_INFLUENCE; i++) {
    if (vertex.BoneIDs[i] < 0) {
        vertex.Weights[i] = weight;
        vertex.BoneIDs[i] = boneID;
        break;
    }
}
}

void Model::ExtractBoneWeightForVertices(std::vector<Vertex>& vertices, aiMesh* mesh, const aiScene* scene){
for (int boneIndex = 0; boneIndex < mesh->mNumBones; boneIndex++) {
    int boneID = -1;
    std::string boneName = mesh->mBones[boneIndex]->mName.C_Str();
    if (m_BoneInfoMap.find(boneName) == m_BoneInfoMap.end())
    {
        BoneInfo newBoneInfo;
        newBoneInfo.ID = m_BoneCounter;
        newBoneInfo.OffsetMatrix = Helpers::ConvertMatrixToGLMFormat(
            mesh->mBones[boneIndex]->mOffsetMatrix);
        m_BoneInfoMap[boneName] = newBoneInfo;
        boneID = m_BoneCounter;
        m_BoneCounter++;
    }
    else
    {
        boneID = m_BoneInfoMap[boneName].ID;
    }
    assert(boneID != -1);
    auto weights = mesh->mBones[boneIndex]->mWeights;
    int numWeights = mesh->mBones[boneIndex]->mNumWeights;

    for (int weightIndex = 0; weightIndex < numWeights; ++weightIndex)
    {
        int vertexId = weights[weightIndex].mVertexId;
        float weight = weights[weightIndex].mWeight;
        assert(vertexId <= vertices.size());
        

        SetVertexBoneData(vertices[vertexId], boneID, weight);
    }
}

This is the calculation used to find the FinalBoneMatrices:

void Animator::CalculateBoneTransform(const NodeData* node,   glm::mat4 parentTransform) {
std::string nodeName = node->Name;
glm::mat4 nodeTransform = node->Transformation;    

Bone* Bone = m_CurrentAnimation->FindBone(nodeName);

if (Bone)
{
    Bone->Update(m_CurrentTime);
    nodeTransform = Bone->GetLocalTransform();
}

glm::mat4 globalTransformation = parentTransform * nodeTransform;

auto boneInfoMap = m_CurrentAnimation->GetBoneIDMap();
if (boneInfoMap.find(nodeName) != boneInfoMap.end())
{
    int index = boneInfoMap[nodeName].ID;
    glm::mat4 offset = boneInfoMap[nodeName].OffsetMatrix;
    // m_FinalBoneMatrices[index] = offset * globalTransformation; // FBX Works this way
    m_FinalBoneMatrices[index] = globalTransformation * offset; // GLTF Works this way

}

for (int i = 0; i < node->ChildrenCount; i++) CalculateBoneTransform(&node->Children[i], globalTransformation);
}

Which is finally called via:

m_Animator->UpdateAnimation(0.016f); // hard coded for now
auto transform = m_Animator->GetFinalBoneMatrices();


shader->UploadUniformMat4Array("u_BoneTransforms", transform);

m_Model.Draw();

Users here will generally not download or peruse your whole repository just to find out whether this is a question they can answer, so relying on an outside link can increase delays before you get help. To make it faster to get answers, it helps to boil down your problem to a Minimal Complete Verifiable Example, and embed in the question itself all the key code required to reproduce the problem. — DMGregory
– DMGregory ♦, Commented Jan 27 at 17:39

Pikalek · Accepted Answer · 2025-01-29 19:59:53Z

I found it, I have a Vertex Buffer being created for OpenGL and I was assigning glVertexAtttribPointer to all of them like so:

void OpenGLVertexArray::AddVertexBuffer(conststd::shared_ptr<VertexBuffer>&vertexBuffer)
{
// Check whether this has a layout.
ASSERT(vertexBuffer->GetLayout().GetElements().size(), "Vertex buffer has no layout!");

glBindVertexArray(m_RendererID);
vertexBuffer->Bind();

uint32_t index = 0;
const auto& layout = vertexBuffer->GetLayout();
for (const auto& element : layout) {
    glEnableVertexAttribArray(index);
    glVertexAttribPointer(index,
        element.GetComponentCount(),
        ShaderDataTypeToOpenGLBaseType(element.Type),
        element.Normalised ? GL_TRUE : GL_FALSE,
        layout.GetStride(),
        (const void*)element.Offset);
    index++;
}

m_VertexBuffers.push_back(vertexBuffer);

}

However, you shouldn't use this when assigning integers. So I had to swap to:

glVertexAttribIPointer(index,
element.GetComponentCount(),
ShaderDataTypeToOpenGLBaseType(element.Type),
layout.GetStride(),
(const void*)element.Offset);

For integers. All calculations you see above are correct.

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