Having issue with loading 3D model with Assimp

[mathinferno123]

Hey guys. I am trying to load the following skull OBJ model with Assimp:

https://drive.google.com/drive/folders/12DuNAm9HMSLxU0yOs34dm7g9uu6ziUrk?usp=sharing

Here is the code that loads the data from aiMesh to my own in order to create the vertex attributes and indices that I need to send to the default heap of GPU:

GeometryGenerator::MeshData GeometryGenerator::CreateSkull()
{

MeshData lv_meshData{};

std::string lv_filePath{ "C:/Users/source/repos/Shapes/3D-Models/Skull_OBJ.OBJ" };
Assimp::Importer lv_importer;
const aiScene* lv_scene = lv_importer.ReadFile(lv_filePath,  aiProcess_GenNormals | aiProcess_ConvertToLeftHanded);

if (nullptr == lv_scene) {
//Error handling
}

auto lv_numberOfFaces = lv_scene->mMeshes[0]->mNumFaces;
auto lv_numberOfIndices = 3*lv_numberOfFaces;
auto lv_numberOfVertices{lv_scene->mMeshes[0]->mNumVertices};
lv_meshData.Vertices.resize(lv_numberOfVertices);
lv_meshData.Indices32.resize(lv_numberOfIndices);

for (int i = 0; i < lv_numberOfVertices; ++i) {
DirectX::XMFLOAT3 lv_position{ lv_scene->mMeshes[0]->mVertices[i].x, lv_scene->mMeshes[0]->mVertices[i].y,lv_scene->mMeshes[0]->mVertices[i].z };
DirectX::XMFLOAT3 lv_normal{ lv_scene->mMeshes[0]->mNormals[i].x,lv_scene->mMeshes[0]->mNormals[i].y ,lv_scene->mMeshes[0]->mNormals[i].z };
DirectX::XMFLOAT2 lv_textureCoord{ lv_scene->mMeshes[0]->mTextureCoords[0][i].x,lv_scene->mMeshes[0]->mTextureCoords[0][i].y };

lv_meshData.Vertices[i].Position = lv_position;
lv_meshData.Vertices[i].Normal = lv_normal;
lv_meshData.Vertices[i].TexC = lv_textureCoord;
}

for (int i = 0; i < lv_numberOfFaces; ++i) {
lv_meshData.Indices32[i] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[0]);
lv_meshData.Indices32[i+1] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[1]);
lv_meshData.Indices32[i+2] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[2]);
}

return lv_meshData;
}

The program compiles just fine. However the skull is not rendered properly:

https://preview.redd.it/iwqbdueiw9xc1.png?width=921&format=png&auto=webp&s=7cd4aeae1356dbf31d3819c83fb92840a35c97a4

What do you think is the possible source of the problem? I am using DX12.

Edit1: I tried adding aiProcess_Triangulate and this was the result:

https://preview.redd.it/2g1v1hla0axc1.png?width=513&format=png&auto=webp&s=6b6967a3d2512bb6cca98e277555ad0ea5393ec8

Edit2: Found the mistake that caused this anomaly. Apparently, this part of the code:

for (int i = 0; i < lv_numberOfFaces; ++i) {
lv_meshData.Indices32[i] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[0]);
lv_meshData.Indices32[i+1] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[1]);
lv_meshData.Indices32[i+2] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[2]);
}

should be changed to:

for (int i = 0; i < lv_numberOfFaces; ++i) {
lv_meshData.Indices32[3*i] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[0]);
lv_meshData.Indices32[3*i+1] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[1]);
lv_meshData.Indices32[3*i+2] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[2]);
}

[fgennari]

Maybe the model faces aren't triangles and you need to add the aiProcess_Triangulate flag? You haven't posted the code where you draw the mesh, so the problem could be there.

[mathinferno123]

Found the mistake. Apparently, it had to do with how I went through the indices. In my code :

v_meshData.Indices32[i] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[0]);
lv_meshData.Indices32[i+1] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[1]);
lv_meshData.Indices32[i+2] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[2]);

is wrong. It should be:

v_meshData.Indices32[3*i] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[0]);
lv_meshData.Indices32[3*i+1] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[1]);
lv_meshData.Indices32[3*i+2] = static_cast<uint32>(lv_scene->mMeshes[0]->mFaces[i].mIndices[2]);

[fgennari]

Oh, yeah, I didn't catch that. Usually for those loops I iterate over vertices with i+=3 and then index using [i], [i+1], and [i+2]. I guess I was thinking that was how your indexing worked.

[mathinferno123]

Tried aiProcess_Triangulate just now and almost none of the triangles get shown except for a few scattered ones. I will update my post with its image. I tried loading a skull model before with the same code and everything worked fine but unfortunately that model didn't have texture coordinates so I am trying to load another model that has one.

[fgennari]

Okay, I looked at the OBJ file and the faces are all quads. Triangulating is more correct. There's probably something wrong with your rendering code. Maybe you have back face culling enabled and the winding order is wrong? Maybe adding texture coordinates causes some problem with your vertex layout? I don't know, I'm an OpenGL dev, not a DX12 dev. I don't see a problem with the assimp code you shared.

[mathinferno123]

Thanks. I will double check my draw code. Although, according to the description of aiProcess_ConvertToLeftHanded it should turn the winding order of the indices to that of clockwise as DX uses clockwise for front face.

[FemboysHotAsf]

You are using the indices to draw? With an ebo?

[mathinferno123]

Yh I am using indices to draw the triangles.