C ++ obj loader纹理坐标搞砸了

Question

我用 C++ 编写了一个简单的 obj 解析器，用于加载顶点、索引和纹理坐标（这就是我需要的所有数据）。

函数如下：

Model* ModelLoader::loadFromOBJ(string objFile, ShaderProgram *shader, GLuint texture)
    {
        fstream file;

        file.open(objFile);
        if (!file.is_open())
        {
            cout << "ModelLoader: " << objFile << " was not found";
            return NULL;
        }

        int vertexCount = 0;
        int indexCount = 0;
        vector<Vector3> vertices;
        vector<Vector2> textureCoordinates;
        vector<Vector2> textureCoordinatesFinal;
        vector<unsigned int> vertexIndices;
        vector<unsigned int> textureIndices;

        string line;
        while (getline(file, line))
        {
            vector<string> splitLine = Common::splitString(line, ' ');

            // v - vertex
            if (splitLine[0] == "v")
            {
                Vector3 vertex(stof(splitLine[1]), stof(splitLine[2]), stof(splitLine[3]));
                vertices.push_back(vertex);
                vertexCount++;
            }
            // vt - texture coordinate
            else if (splitLine[0] == "vt")
            {
                Vector2 textureCoordinate(stof(splitLine[1]), 1 - stof(splitLine[2]));
                textureCoordinates.push_back(textureCoordinate);
            }
            // f - face
            else if (splitLine[0] == "f")
            {
                vector<string> faceSplit1 = Common::splitString(splitLine[1], '/');
                vector<string> faceSplit2 = Common::splitString(splitLine[2], '/');
                vector<string> faceSplit3 = Common::splitString(splitLine[3], '/');

                unsigned int vi1 = stoi(faceSplit1[0]) - 1;
                unsigned int vi2 = stoi(faceSplit2[0]) - 1;
                unsigned int vi3 = stoi(faceSplit3[0]) - 1;
                unsigned int ti1 = stoi(faceSplit1[1]) - 1;
                unsigned int ti2 = stoi(faceSplit2[1]) - 1;
                unsigned int ti3 = stoi(faceSplit3[1]) - 1;

                vertexIndices.push_back(vi1);
                vertexIndices.push_back(vi2);
                vertexIndices.push_back(vi3);
                textureIndices.push_back(ti1);
                textureIndices.push_back(ti2);
                textureIndices.push_back(ti3);

                indexCount += 3;
            }
        }

        // rearanging textureCoordinates into textureCoordinatesFinal based on textureIndices
        for (int i = 0; i < indexCount; i++)
            textureCoordinatesFinal.push_back(textureCoordinates[textureIndices[i]]);

        Model *result = new Model(shader, vertexCount, &vertices[0], NULL, texture, indexCount, &textureCoordinatesFinal[0], &vertexIndices[0]);
        models.push_back(result);

        return result;
    }

如您所见，我考虑了 1 - texCoord.y（因为 blender 和 opengl 使用不同的纹理坐标系）。我还在 while 循环后根据纹理索引排列纹理坐标。

但是，我尝试渲染的模型的纹理乱七八糟。这是一个例子：

纹理混乱

我什至用一个立方体尝试过，我在搅拌机中打开它并应用了一个非常简单的砖块纹理。在 1 或 2 个面孔中，纹理很好并且可以正常工作，然后在其他一些面孔中，其中 1 个的纹理正确，而其他的则出现拉伸（与上图相同）。

Answer 1

要定义一个网格，只有一个索引列表来索引顶点属性。顶点属性（在你的例子中是顶点和纹理坐标）形成一个记录集，由这些索引引用。

这导致，每个顶点坐标可能在列表中出现多次，每个纹理坐标可能在列表中出现多次。但是每个顶点和纹理坐标的组合都是唯一的。

采用 vertexIndices 和 textureIndices 创建唯一的顶点和纹理坐标对（verticesFinal、textureCoordinatesFinal）。
创建新的 attribute_indices，索引对。
使用临时容器 attribute_pairs 来管理唯一对并识别它们的索引：

#include <vector>
#include <map>

// input
std::vector<Vector3> vertices;
std::vector<Vector2> textureCoordinates;
std::vector<unsigned int> vertexIndices;
std::vector<unsigned int> textureIndices;

std::vector<unsigned int> attribute_indices;  // final indices
std::vector<Vector3> verticesFinal;           // final vertices buffer
std::vector<Vector2> textureCoordinatesFinal; // final texture coordinate buffer

// map a pair of indices to the final attribute index
std::map<std::pair<unsigned int, unsigned int>, unsigned int> attribute_pairs; 

// vertexIndices.size() == textureIndices.size()
for ( size_t i = 0; i < vertexIndices.size(); ++ i )
{
    // pair of vertex index an texture index
    auto attr = std::make_pair( vertexIndices[i], textureIndices[i] );

    // check if the pair aready is a member of "attribute_pairs"
    auto attr_it = attribute_pairs.find( attr );

    if ( attr_it == attribute_pairs.end() )
    {
        // "attr" is a new pair

        // add the attributes to the final buffers
        verticesFinal.push_back( vertices[attr.first] );
        textureCoordinatesFinal.push_back( textureCoordinates[attr.first] );

        // the new final index is the next index
        unsigned int new_index = (unsigned int)attribute_pairs.size();
        attribute_indices.push_back( new_index );

        // add the new map entry 
        attribute_pairs[attr] = new_index;
    }
    else
    {
        // the pair "attr" already exists: add the index which was found in the map
        attribute_indices.push_back( attr_it->second );
    }
}

注意顶点坐标的数量（verticesFinal.size()）等于纹理坐标的数量（textureCoordinatesFinal.size()）。但是索引的数量（attribute_indices.size()）完全不同。

// verticesFinal.size() == textureCoordinatesFinal.size()
Model *result = new Model(
    shader, 
    verticesFinal.size(),
    verticesFinal.data(),
    NULL, texture,
    attribute_indices.size(),
    textureCoordinatesFinal.data(),
    attribute_indices.data() );

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