ASSIMP : mNumMeshes is 0

Question

When I was following the LearnOpenGL, a problem come up: I can't figure out why the scene->mRootNode->mNumMeshes is 0. However the scene has been imported rightly (I guess, 'cause scene->mNumMeshes is 7).

void Model::loadModel(std::string path)
{
    Assimp::Importer import;
    const aiScene *scene = import.ReadFile(path, aiProcess_Triangulate | aiProcess_FlipUVs); 

    if (scene == nullptr || !scene->mRootNode || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE)
    { 
        std::cout << "ERROR::ASSIMP::" << import.GetErrorString() << std::endl;
        return;
    }
    directory = path.substr(0, path.find_last_of('/'));

    processNode(scene->mRootNode, scene);
}

void Model::processNode(aiNode *node, const aiScene *scene)
{
    for (unsigned int i = 0; i < node->mNumMeshes; i++)
    {
        aiMesh *mesh = scene->mMeshes[node->mMeshes[i]];
        meshes.push_back(processMesh(mesh, scene));
        std::cout << "SUCCESS::ASSIMP::PROCESSED:" << i << std::endl;
    }

    for (unsigned int i = 0; i < node->mNumMeshes; i++)
        processNode(node->mChildren[i], scene);
}

Answer 1

Meshes are not necessarily attached to the root node. They can also be attached to any of the child nodes (or children's child nodes). Having a scene which contains 7 meshes with scene->mRootNode->mNumMeshes beeing 0 is perfectly valid.

But, the recursive loop in your code is wrong. You have to iterate over node->mNumChildren instead of node->mNumMeshes:

for (unsigned int i = 0; i < node->mNumChildren; i++)
    processNode(node->mChildren[i], scene);