c++ - OpenGL - 在 ubuntu 中的线程上创建 vbo？

Question

我有一个应用程序，其中服务器上有远程网格数据。其中一些网格有 400k 个顶点，因此在下载过程中需要线程。在一个线程上运行所有内容时我没有问题，所有代码都工作正常，除了当我将下载的缓冲区上传到线程版本中的 openGL 土地时。尝试使用 opengl 调用创建 vbo 时，我最终崩溃了。应用程序通常会在 glGenBuffers 上出现段错误。我在尝试让 OpenGL 调用线程安全时阅读的一些示例涉及特定的 Windows api 和特定于平台的内容，这些内容在 x11 ubuntu 环境中没有太大帮助。

所以我希望以前做过这件事的人能给我指点一些电话，这样在重新设计一个工作 block 之前这可能是可行的。

我的加载代码非常简单轻量，vbo上传是glGenBuffer、glBind、glBufferData调用的典型步骤:

///
/// \brief The LoadMeshThread class
///     Thread to load a mesh (geometry data) from database
///
class LoadMeshThread : public vtrus::core::Thread
{
    CLASSEXTENDS(LoadMeshThread, vtrus::core::Thread)
    ADD_TO_CLASS_MAP
public:
    VTRUS_HOST
    LoadMeshThread( Chunk* chunk, uint32_t mapID, ChunkGrid* chunkVolume ) :
      super(),
      ChunkToLoadMesh(chunk),
      CpuVertices(NULL),
      CpuNormals(NULL),
      VertexCount(0),
      ChunkVolume(chunkVolume)
    {
        printf("Loading [%s]\n", chunk->GridLocation.ToString().str());
        MapID = mapID;

        ChunkToLoadMesh->AddRef();
        ChunkGrid::LiveLoadThreads++;
    }

    ///
    /// \brief ~LoadHashThread
    /// Destroyed after pthread has ended
    virtual ~LoadMeshThread()
    {
        vprintf(vtrus::debug::Threading, "[%d]\n", this->ThreadID);
        ChunkToLoadMesh->Release();
        ChunkGrid::LiveLoadThreads--;
        delete [] CpuVertices;
        delete [] CpuNormals;
    }

    ///
    /// \brief Run
    ///  Called by base class when the pthread is created
    virtual void Run();

    ///
    /// \brief ReadFromDataBase
    ///
    void ReadFromDataBase();

private:
    ChunkGrid* ChunkVolume; //Access to world data
    uint32_t MapID;
    vtrus::slam::Chunk* ChunkToLoadMesh;
    GLfloat* CpuVertices;
    GLfloat* CpuNormals;
    int VertexCount;
};

///
/// \brief LoadMeshThread::ReadFromDataBase
/// Calls into mysql and grabs the blobs containing the data
void LoadMeshThread::ReadFromDataBase()
{
    Eigen::Vector3i chunkR3 = ChunkToLoadMesh->GridLocation.ToEigen();
    uint32_t chunkID = R3ToChunkID( chunkR3 );
    vtrus::database::DataBase* vtrusDB = vtrus::database::DataBase::GetInstance();

    {
        vtrusDB->Driver->threadInit();
        {
            try
            {
                vtrus::core::String connectionString = vtrusDB->GetConnectionString();
                sql::Connection* connection = vtrusDB->Driver->connect(connectionString.str(), "gobble", "gobblegobble" );
                connection->setSchema( "gobble" );

                sql::ResultSet* result = vtrusDB->GetMeshData( connection, chunkID, MapID, 1 );

                if( result != NULL && result->next() )
                {
                    std::istream* verticesBlob = result->getBlob("VertexBuffer");
                    std::istream* normalsBlob = result->getBlob("NormalsBuffer");
                    VertexCount = result->getInt("VertexCount");

                    uint bufferSize = VertexCount*sizeof(vtrus::geometry::Vec3f);
                    CpuVertices = new GLfloat[bufferSize];
                    CpuNormals = new GLfloat[bufferSize];
                    //printf("Loading %d entries \n", entryCount );
                    verticesBlob->read( reinterpret_cast<char*>(&CpuVertices[0]), (std::streamsize)bufferSize );
                    normalsBlob->read( reinterpret_cast<char*>(&CpuNormals[0]), (std::streamsize)bufferSize );

                    delete verticesBlob;
                    delete normalsBlob;
                }

                delete result;
                delete connection;
            }
            catch ( sql::SQLException * exception )
            {
                //do nothing
                printf("WARNING: SqlException on Loading\n");
            }
        }
        vtrusDB->Driver->threadEnd();
    }
}

void LoadMeshThread::Run()
{
    vtrus::core::ScopedTimer timer("**** LoadHashThread::Run ****");

    vprintf(vtrus::debug::Threading, "[%d]\n", this->ThreadID);
    int numAttempts = 0;
    const int maxAttenpts = 10;
    uint countRemaining = 0;
    uint maxCount = 0;

    ReadFromDataBase();

    if( VertexCount > 0 )
    {
        printf("Creating [%d] vertices\n", VertexCount);
        //CRASH here when the mesh constructor calls glGenBuffer          
        vtrus::resources::Mesh* newMesh = new vtrus::resources::Mesh(VertexCount);
        //upload cpu vertices / normals to GPU

        glBindBuffer( GL_ARRAY_BUFFER, newMesh->GetVertexBuffer()->bo );
        glBufferData(GL_ARRAY_BUFFER, VertexCount * sizeof(vtrus::geometry::Vec3f), &CpuVertices[0], GL_STATIC_DRAW);

        glBindBuffer( GL_ARRAY_BUFFER, newMesh->GetNormalsBuffer()->bo);
        glBufferData(GL_ARRAY_BUFFER, VertexCount * sizeof(vtrus::geometry::Vec3f), &CpuNormals[0], GL_STATIC_DRAW);

        glBindBuffer( GL_ARRAY_BUFFER, 0 );

        ChunkVolume->AddMesh(newMesh, ChunkToLoadMesh);
        newMesh->Release();

        ChunkToLoadMesh->IsLoaded = true;
        ChunkToLoadMesh->IsSaved = true;
        ChunkToLoadMesh->SavedBlockCount = maxCount;
    }

    //Access mutex
    ChunkToLoadMesh->IsLoading = false;
}

Answer 1

在可以使用任何 glXXX 命令之前，必须将 gl 上下文设置为将使用这些命令的线程的当前上下文。

在 X11 世界中，要使用的命令是 glXMakeContextCurrent 或更早但仍然有效的 glXMakeCurrent。参见 glX doc .如果您正在使用一些为您处理 gl-context 的库，请在其文档中搜索。

您可以在一个 gl-context 中上传数据并在另一个 gl-context 中呈现它。为此，两个上下文都必须“共享”，这是您通常在它们的构造函数中执行的操作。
但是，如果您的显卡无法在渲染时读取数据，则不会有很大的性能改进。