Assimp does not correctly load multiple meshes from one obj file

Question

The obj files I am trying to load have multiple -o flags, so there are multiple meshes. I am trying to load them into only 1 VAO, and I will draw them by first recording each mesh's offset and size. I have noted that the offset and size are in terms of number of vertices instead of faces, so they are multiplied by 3. For example, the first mesh starts at offset 0, and its size is mesh1's mNumberFaces * 3, and the second mesh starts at offset mesh1's mNumberFaces * 3, and its size is mesh2's mNumberFaces * 3. However, it seems only the first mesh is drawn correctly, and the rest of the meshes are all distorted somehow. This is my loading logic:

Object* obj = new Object(objName);
// Initialize the meshes in the obj file one by one
std::vector<glm::vec3> vert, norm;
std::vector<glm::vec2> text;
std::vector<glm::ivec3> indices;
int vertexOffset = 0;
std::cout << objName << " numMeshes: " << pScene->mNumMeshes << std::endl;
for (unsigned int i = 0; i < pScene->mNumMeshes; i++) {
    std::cout << objName << ": vOffset " << vertexOffset << " numV " << pScene->mMeshes[i]->mNumFaces * 3 << std::endl;
    aiMesh* pMesh = pScene->mMeshes[i];
    aiVector3D Zero3D(0.0f, 0.0f, 0.0f);
    for (unsigned int j = 0; j < pMesh->mNumVertices; j++) {
        vert.push_back(glm::vec3(pMesh->mVertices[j].x, pMesh->mVertices[j].y, pMesh->mVertices[j].z));
        norm.push_back(glm::vec3(pMesh->mNormals[j].x, pMesh->mNormals[j].y, pMesh->mNormals[j].z));
        aiVector3D textCoord = pMesh->HasTextureCoords(0) ? pMesh->mTextureCoords[0][j] : Zero3D;
        text.push_back(glm::vec2(textCoord.x, textCoord.y));
    }

    for (unsigned int j = 0; j < pMesh->mNumFaces; j++) {
        aiFace face = pMesh->mFaces[j];
        indices.push_back(glm::ivec3(face.mIndices[0], face.mIndices[1], face.mIndices[2]));
    }

    aiMaterial* mtl = pScene->mMaterials[pMesh->mMaterialIndex];
    std::string meshName = std::string(pMesh->mName.C_Str());
    Mesh* mesh = new Mesh(meshName, loadMaterial(mtl), vertexOffset, pMesh->mNumFaces * 3);
    obj->meshList.push_back(mesh);
    vertexOffset = vertexOffset + 3 * pMesh->mNumFaces;
}

//create the obj's node structure
//obj->root = processNode(pScene->mRootNode, obj->meshList);

//send the data to the gpu
GLuint vao;
GLuint vbo[3];
GLuint ebo;

glcheck(glGenVertexArrays(1, &vao));
glcheck(glBindVertexArray(vao));

glcheck(glGenBuffers(3, vbo));
glcheck(glBindBuffer(GL_ARRAY_BUFFER, vbo[0]));
glcheck(glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec3) * vert.size(), vert.data(), GL_STATIC_DRAW));
glcheck(glEnableVertexAttribArray(0));
glcheck(glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0));

glcheck(glBindBuffer(GL_ARRAY_BUFFER, vbo[1]));
glcheck(glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec3) * norm.size(), norm.data(), GL_STATIC_DRAW));
glcheck(glEnableVertexAttribArray(1));
glcheck(glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, 0));

glcheck(glBindBuffer(GL_ARRAY_BUFFER, vbo[2]));
glcheck(glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec2) * text.size(), text.data(), GL_STATIC_DRAW));
glcheck(glEnableVertexAttribArray(2));
glcheck(glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 0, 0));

glcheck(glGenBuffers(1, &ebo));
glcheck(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo));
glcheck(glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(glm::ivec3) * indices.size(), indices.data(), GL_STATIC_DRAW));

// Unbind the VBO/VAO
glcheck(glBindVertexArray(0));
//glcheck(glBindBuffer(GL_ARRAY_BUFFER, 0));
//glcheck(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0));

obj->vao = vao; //shared vao variable
objMap[objName] = obj;
objList.push_back(obj);

return obj;

This is my drawing logic:

for (int i = 0; i < instObj->meshList.size(); i++) {
    Mesh* mesh = instObj->meshList[i];
    glcheck(glDrawElements(GL_TRIANGLES, mesh->size, GL_UNSIGNED_INT, (GLvoid*)(sizeof(GLuint) * mesh->vertexOffset)));
}

This is the first mesh, which is drawn correctly first mesh

The second mesh and onward are all messed up however, second mesh

The complete mesh enter image description here

Assimp does not correctly load multiple meshes from one obj file

0 Answers0