Question

我正在尝试编写一个程序，该程序使用OpenGL的三角形邻接功能（GL_TRIANGLES_ADJACENCY）来确定来自本地光源的网格轮廓。我正在使用ASSIMP来加载我的网格，就加载和显示网格而言，一切似乎都正常工作。不幸的是，我编写的用于存储相邻三角形索引的代码似乎没有正常工作。

index[0] = mesh.mFaces[i].mIndices[0];
index[2] = mesh.mFaces[i].mIndices[1];
index[4] = mesh.mFaces[i].mIndices[2];
index[1] = findAdjacentIndex( mesh, index[0], index[2], index[4] );
index[3] = findAdjacentIndex( mesh, index[0], index[2], index[4] );
index[5] = findAdjacentIndex( mesh, index[0], index[2], index[4] );

我的算法背后的基本思想是，给定网格和来自该网格的三个索引，找到共享网格的网格的所有面（应该是1或2，具体取决于是否存在相邻的面）第一个和第二个顶点之间的边缘。然后，返回不使用原始传递三角形的第三个索引的三角形的第三个索引。这样，相同的算法可以按顺序用于三角形的所有索引。

unsigned int Mesh::findAdjacentIndex(const aiMesh& mesh, const unsigned int index1, const unsigned int index2, const unsigned int index3) {
    std::vector<unsigned int> indexMap[2];

    // first pass: find all faces that use the first index
    for( unsigned int i=0; i<mesh.mNumFaces; ++i ) {
        unsigned int*& indices = mesh.mFaces[i].mIndices;
        if( indices[0] == index1 || indices[1] == index1 || indices[2] == index1 ) {
            indexMap[0].push_back(i);
        }
    }

    // second pass: find the two faces that share the second index
    for( unsigned int i=0; i<indexMap[0].size(); ++i ) {
        unsigned int*& indices = mesh.mFaces[indexMap[0][i]].mIndices;
        if( indices[0] == index2 || indices[1] == index2 || indices[2] == index2 ) {
            indexMap[1].push_back(i);
        }
    }

    // third pass: find the face that does NOT use the third index and return its third index
    for( unsigned int i=0; i<indexMap[1].size(); ++i ) {
        unsigned int*& indices = mesh.mFaces[indexMap[1][i]].mIndices;
        if( indices[0] != index3 && indices[1] != index3 && indices[2] != index3 ) {
            if( indices[0] != index1 && indices[0] != index2 ) {
                return indices[0];
            }
            if( indices[1] != index1 && indices[1] != index2 ) {
                return indices[1];
            }
            if( indices[2] != index1 && indices[2] != index2 ) {
                return indices[2];
            }
        }
    }

    // no third index was found, this means there is no face adjacent to this one.
    // return primitive restart index
    return restartIndex;
}

基于我对我所写内容的理解，上述函数应该完全适用于从OpenGL规范中获取的示例图像：

Triangle Adjacency Example

不幸的是，我的功能不适用于我的任何现实世界网格，我不知道为什么。例如，通过函数传递一个简单的框网格通常会返回0作为每个顶点的相邻索引，这对我来说没什么意义。结果是邻接没有正确上传，我的对象得到了不正确的轮廓......

如果这里的任何人能够解决出错的问题以及我能做些什么来解决它，我将非常感激。如果需要，我也很乐意提供更多信息。

Answer 1

你正在变得比它需要的更复杂。您想要搜索共享特定边的三角形并返回第三个顶点。然后就这样做。

for(unsigned int i=0; i<mesh.mNumFaces; ++i ) {
    unsigned int*& indices = mesh.mFaces[i].mIndices;
    for(int edge = 0; edge < 3; ++edge) { //iterate all edges of the face
        unsigned int v1 = indices[edge]; //first edge index
        unsigned int v2 = indices[(edge + 1) % 3]; //second edge index
        unsigned int vOpp = indices[(edge + 2) % 3]; //index of opposite vertex
        //if the edge matches the search edge and the opposite vertex does not match
        if(((v1 == index1 && v2 == index2) || (v2 == index1 && v1 == index2)) && vOpp != index3)
            return vOpp; //we have found the adjacent vertex
    }
}
return -1;

此外，您需要更改通话。如果使用相同的参数调用该函数三次，则会得到相同的结果：

index[1] = findAdjacentIndex( mesh, index[0], index[2], index[4] );
index[3] = findAdjacentIndex( mesh, index[2], index[4], index[0] );
index[5] = findAdjacentIndex( mesh, index[4], index[0], index[2] );

OpenGL三角形邻接计算

1 个答案: