使用 FBX SDK 获取索引

Posted 2023-03-23

【中文标题】使用 FBX SDK 获取索引

【英文标题】：Fetching indices with FBX SDK

【发布时间】：2018-11-28 07:45:34

【问题描述】：

我无法确定使用什么来从 FBX 文件中获取索引。恢复数据非常好（至少对于位置而言），但我似乎无法找到如何获取索引。

免责声明：对于长段代码感到抱歉，如果您认为某些部分确实不必要，请随时编辑。

我目前正在获取这样的数据：

// Recovering geometry
for (int meshIndex = 0; meshIndex < scene->GetGeometryCount(); ++meshIndex)

  const auto mesh = static_cast<FbxMesh*>(scene->GetGeometry(meshIndex));

  // Recovering positions
  int currentVertIndex = points_coords.size();
  points_coords.resize(currentVertIndex + mesh->GetControlPointsCount(), std::vector<coord_type>(3));

  for (int vertIndex = 0; vertIndex < mesh->GetControlPointsCount(); ++vertIndex, ++currentVertIndex)
  
    const auto& vertPos = mesh->GetControlPointAt(vertIndex);

    points_coords[currentVertIndex][0] = vertPos[0]; // X position
    points_coords[currentVertIndex][1] = vertPos[1]; // Y position
    points_coords[currentVertIndex][2] = vertPos[2]; // Z position
  

  // Iterate over normals with mesh->GetElementNormal()->GetDirectArray().GetCount()

  // Iterate over texcoords with mesh->GetElementUV()->GetDirectArray().GetCount()

至于索引，我正在迭代面（多边形）并获取它们的顶点索引：

// Fetching positions' indices
int currentPosPolyIndex = face_indices.size();
face_indices.resize(currentPosPolyIndex + mesh->GetPolygonCount());

for (int polyIndex = 0; polyIndex < mesh->GetPolygonCount(); ++polyIndex, ++currentPosPolyIndex)

  const auto polySize = mesh->GetPolygonSize(polyIndex);
  face_indices[currentPosPolyIndex].resize(polySize);

  for (int polyVertIndex = 0; polyVertIndex < polySize; ++polyVertIndex)
    face_indices[currentPosPolyIndex][polyVertIndex] = mesh->GetPolygonVertex(polyIndex, polyVertIndex);

这样做对于只包含一个网格的 FBX 效果很好，但是当有多个网格时，它似乎无法缝合面。如果这来自我正在使用的数据结构，我将进一步彻底调查，但如果有人发现这有问题，请告诉我。

问题在于法线和 texcoords 的索引，我不知道如何获取。目前我正在检查两者的映射模式，并尝试相应地填充数据：

  const auto texMapping = mesh->GetElementUV()->GetMappingMode();

  if (texMapping == FbxLayerElement::EMappingMode::eByControlPoint)
  
    std::cout << "[FbxFileReader] Mapping mesh's texture coordinates by vertex." << std::endl;

    texture_face_indices.resize(texture_face_indices.size() + mesh->GetPolygonCount());

    std::copy(face_indices.cend() - mesh->GetPolygonCount(), face_indices.cend(), texture_face_indices.end() - mesh->GetPolygonCount());
  
  else if (texMapping == FbxLayerElement::EMappingMode::eByEdge)
  
    std::cout << "[FbxFileReader] Mapping mesh's texture coordinates by halfedge." << std::endl;
  
  else if (texMapping == FbxLayerElement::EMappingMode::eByPolygon || texMapping == FbxLayerElement::EMappingMode::eByPolygonVertex)
  
    std::cout << "[FbxFileReader] Mapping mesh's texture coordinates by face" << (texMapping == FbxLayerElement::EMappingMode::eByPolygonVertex ? " vertices" : "") << '.' << std::endl;

    int currentTexPolyIndex = texture_face_indices.size();
    texture_face_indices.resize(currentTexPolyIndex + mesh->GetPolygonCount());

    for (int polyIndex = 0; polyIndex < mesh->GetPolygonCount(); ++polyIndex, ++currentTexPolyIndex)
    
      if (texMapping == FbxLayerElement::EMappingMode::eByPolygonVertex)
      
        const auto polySize = mesh->GetPolygonSize(polyIndex);
        texture_face_indices[currentTexPolyIndex].resize(polySize);

        for (int polyVertIndex = 0; polyVertIndex < polySize; ++polyVertIndex)
          texture_face_indices[currentTexPolyIndex][polyVertIndex] = mesh->GetTextureUVIndex(polyIndex, polyVertIndex);
      
      else
      
        // Fetch face's texcoords & add it
        //texture_face_indices[currentTexPolyIndex].emplace_back(...);
      
    
  
  else if (texMapping == FbxLayerElement::EMappingMode::eAllSame)
  
    std::cout << "[FbxFileReader] Mapping mesh's texture coordinates by mesh." << std::endl;
  
  else
  
    std::cerr << "[FbxFileReader] Couldn't handle mesh's texture coordinates' mapping mode." << std::endl;
  

我现在只处理面部 [顶点] 案例，我认为这对于 texcoords 是正确的（我目前没有获得材料，所以我无法检查）。但是对于法线，我找不到任何有关获取索引的信息；这就是为什么我只复制与位置相同的索引，我认为这是完全错误的：

  // Same checks for normals
  else if (normMapping == FbxLayerElement::EMappingMode::eByPolygon || normMapping == FbxLayerElement::EMappingMode::eByPolygonVertex)
  
    std::cout << "[FbxFileReader] Mapping mesh's normals by face" << (normMapping == FbxLayerElement::EMappingMode::eByPolygonVertex ? " vertices" : "") << "." << std::endl;

    int currentNormPolyIndex = normal_face_indices.size();
    normal_face_indices.resize(currentNormPolyIndex + mesh->GetPolygonCount());

    for (int polyIndex = 0; polyIndex < mesh->GetPolygonCount(); ++polyIndex, ++currentNormPolyIndex)
    
      if (normMapping == FbxLayerElement::EMappingMode::eByPolygonVertex)
      
        const auto polySize = mesh->GetPolygonSize(polyIndex);
        normal_face_indices[currentNormPolyIndex].resize(polySize);

        for (int polyVertIndex = 0; polyVertIndex < polySize; ++polyVertIndex)
          normal_face_indices[currentNormPolyIndex][polyVertIndex] = face_indices[currentNormPolyIndex][polyVertIndex];
      
      else  /*...*/ 
    
  

这是恢复索引的正确方法吗？我错过了什么吗？

【参考方案1】：

首先你不应该把所有网格的数据放到同一个数组中。每个网格可以有不同的材质，所以应该用单独的drawcall来绘制。但如果这不是你的选择，那么错误就在那一行：

face_indices[currentPosPolyIndex][polyVertIndex] = mesh->GetPolygonVertex(polyIndex, polyVertIndex);

你把顶点放在一个数组中，像这样

[(1-st mesh) V1, V2, V3, ..., (2-nd mesh) V52, V53, V54, ...]

但是mesh->GetPolygonVertex(polyIndex, polyVertIndex) 返回的索引相对于当前网格，所以第二个网格不是从V52 开始，而是从V1 开始。所以你应该计算一些偏移量。

int currentVertIndex = points_coords.size();
int meshVertIndexStart = currentVertIndex;
...
for (int polyVertIndex = 0; polyVertIndex < polySize; ++polyVertIndex)
    face_indices[currentPosPolyIndex][polyVertIndex] = meshVertIndexStart + mesh->GetPolygonVertex(polyIndex, polyVertIndex);

如果您获得索引，则法线和 UV 更好地进入同一个循环。这是一些代码

FbxVector4 getNormal(FbxGeometryElementNormal* normalElement, int polyIndex, int posIndex) 
    if (normalElement->GetMappingMode() == FbxGeometryElement::eByControlPoint) 
        if (normalElement->GetReferenceMode() == FbxGeometryElement::eDirect)
            return normalElement->GetDirectArray().GetAt(posIndex);
        int i = normalElement->GetIndexArray().GetAt(posIndex);
        return normalElement->GetDirectArray().GetAt(i);
    
    else if (normalElement->GetMappingMode() == FbxGeometryElement::eByPolygonVertex) 
        if (normalElement->GetReferenceMode() == FbxGeometryElement::eDirect)
            return normalElement->GetDirectArray().GetAt(polyIndex);
        int i = normalElement->GetIndexArray().GetAt(polyIndex);
        return normalElement->GetDirectArray().GetAt(i);
    
    return FbxVector4();


FbxVector2 getUV(FbxGeometryElementUV* uvElement, int polyIndex, int posIndex) 
    if (uvElement->GetMappingMode() == FbxGeometryElement::eByControlPoint) 
        if (uvElement->GetReferenceMode() == FbxGeometryElement::eDirect)
            return uvElement->GetDirectArray().GetAt(posIndex);
        int i = uvElement->GetIndexArray().GetAt(posIndex);
        return uvElement->GetDirectArray().GetAt(i);
    
    else if (uvElement->GetMappingMode() == FbxGeometryElement::eByPolygonVertex) 
        if (uvElement->GetReferenceMode() == FbxGeometryElement::eDirect)
            return uvElement->GetDirectArray().GetAt(polyIndex);
        int i = uvElement->GetIndexArray().GetAt(polyIndex);
        return uvElement->GetDirectArray().GetAt(i);
    
    return FbxVector2();


...

int vertNum = 0;

for (int polyIndex = 0; polyIndex < mesh->GetPolygonCount(); ++polyIndex, ++currentPosPolyIndex) 
    const auto polySize = mesh->GetPolygonSize(polyIndex);
    face_indices[currentPosPolyIndex].resize(polySize);

    for (int polyVertIndex = 0; polyVertIndex < polySize; ++polyVertIndex) 
        int vertIndex = mesh->GetPolygonVertex(polyIndex, polyVertIndex);
        face_indices[currentPosPolyIndex][polyVertIndex] = meshVertIndexStart + vertIndex;

        FbxVector4 normal = getNormal(mesh->GetElementNormal(), vertNum, vertIndex);
        FbxVector2 uv = getUV(mesh->GetElementUV(), vertNum, vertIndex);
        vertNum++;