C++ 在Windows上创建并行屏幕外OpenGL上下文

我正在尝试设置并行多GPU屏幕外渲染上下文。我使用了《OpenGL洞察》一书，第27章，“NVIDIA Quadro上的多GPU渲染”。我也研究了WGLCreateAffinityDYDCNV，但仍然无法确定它

我的机器有2个NVidia Quadro 4000卡（无SLI）。运行在64位Windows 7上。 我的工作流程如下：

使用GLFW创建默认窗口上下文

映射GPU设备

销毁默认的GLFW上下文

为每个设备创建新的GL上下文（当前仅尝试一个）

为每个上下文设置boost线程，并使其在该线程中成为当前线程

在每个线程上分别运行渲染过程。（无资源共享）

所有内容都是在没有错误的情况下创建并运行的，但一旦我尝试从屏幕外FBO读取像素，我会在这里得到一个空指针：

GLubyte* ptr  = (GLubyte*)glMapBuffer(GL_PIXEL_PACK_BUFFER, GL_READ_ONLY);

同时，glError返回“未知错误”

我认为可能是多线程的问题，但相同的设置在单线程上运行时会给出相同的结果。 所以我相信这与环境创造有关

我是这样做的：

  ////Creating default window with GLFW here .
      .....
         .....

创建屏幕外上下文：

  PIXELFORMATDESCRIPTOR pfd =
{
    sizeof(PIXELFORMATDESCRIPTOR),
    1,
    PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,    //Flags
    PFD_TYPE_RGBA,            //The kind of framebuffer. RGBA or palette.
    24,                        //Colordepth of the framebuffer.
    0, 0, 0, 0, 0, 0,
    0,
    0,
    0,
    0, 0, 0, 0,
    24,                        //Number of bits for the depthbuffer
    8,                        //Number of bits for the stencilbuffer
    0,                        //Number of Aux buffers in the framebuffer.
    PFD_MAIN_PLANE,
    0,
    0, 0, 0
};

void  glMultiContext::renderingContext::createGPUContext(GPUEnum gpuIndex){

    int    pf;
    HGPUNV hGPU[MAX_GPU];
    HGPUNV GpuMask[MAX_GPU];

    UINT displayDeviceIdx;
    GPU_DEVICE gpuDevice;
    bool bDisplay, bPrimary;
    // Get a list of the first MAX_GPU GPUs in the system
    if ((gpuIndex < MAX_GPU) && wglEnumGpusNV(gpuIndex, &hGPU[gpuIndex])) {

        printf("Device# %d:\n", gpuIndex);

        // Now get the detailed information about this device:
        // how many displays it's attached to
        displayDeviceIdx = 0;
        if(wglEnumGpuDevicesNV(hGPU[gpuIndex], displayDeviceIdx, &gpuDevice))
        {   

            bPrimary |= (gpuDevice.Flags & DISPLAY_DEVICE_PRIMARY_DEVICE) != 0;
            printf(" Display# %d:\n", displayDeviceIdx);
            printf("  Name: %s\n",   gpuDevice.DeviceName);
            printf("  String: %s\n", gpuDevice.DeviceString);
            if(gpuDevice.Flags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP)
            {
                printf("  Attached to the desktop: LEFT=%d, RIGHT=%d, TOP=%d, BOTTOM=%d\n",
                    gpuDevice.rcVirtualScreen.left, gpuDevice.rcVirtualScreen.right, gpuDevice.rcVirtualScreen.top, gpuDevice.rcVirtualScreen.bottom);
            }
            else
            {
                printf("  Not attached to the desktop\n");
            }

            // See if it's the primary GPU
            if(gpuDevice.Flags & DISPLAY_DEVICE_PRIMARY_DEVICE)
            {
                printf("  This is the PRIMARY Display Device\n");
            }


        }

        ///=======================   CREATE a CONTEXT HERE 
        GpuMask[0] = hGPU[gpuIndex];
        GpuMask[1] = NULL;
        _affDC = wglCreateAffinityDCNV(GpuMask);

        if(!_affDC)
        {
            printf( "wglCreateAffinityDCNV failed");                  
        }

    }

    printf("GPU context created");
}

glMultiContext::renderingContext *
    glMultiContext::createRenderingContext(GPUEnum gpuIndex)
{
    glMultiContext::renderingContext *rc;

    rc = new renderingContext(gpuIndex);

    _pixelFormat = ChoosePixelFormat(rc->_affDC, &pfd);

    if(_pixelFormat == 0)
    {

        printf("failed to  choose pixel format");
        return false;
    }

     DescribePixelFormat(rc->_affDC, _pixelFormat, sizeof(pfd), &pfd);

    if(SetPixelFormat(rc->_affDC, _pixelFormat, &pfd) == FALSE)
    {
        printf("failed to set pixel format");
        return false;
    }

    rc->_affRC = wglCreateContext(rc->_affDC);


    if(rc->_affRC == 0)
    {
        printf("failed to create gl render context");
        return false;
    }


    return rc;
}

//Call at the end to make it current :


 bool glMultiContext::makeCurrent(renderingContext *rc)
{
    if(!wglMakeCurrent(rc->_affDC, rc->_affRC))
    {

        printf("failed to make context current");
        return false;
    }

    return true;
}

    ////  init OpenGL objects and rendering here :

     ..........
     ............

---

最后我自己解决了这些问题。第一个问题是，我在将另一个设备上下文设置为当前后调用了glfwTerminate。这可能也卸载了新的上下文。

---

第二个问题是我与boost线程的“无关联性”。我未能初始化自定义线程中所有与渲染相关的对象，因为我在设置线程之前调用了rc init object过程，如上面的示例所示

据我所知，大多数代码看起来都很好。当然，这不是完整的代码，很多奇怪的东西可能隐藏在代码行之间。

GPUThread::GPUThread(void)
{
    _thread =NULL;
    _mustStop=false;
    _frame=0;


    _rc =glMultiContext::getInstance().createRenderingContext(GPU1);
    assert(_rc);

    glfwTerminate(); //terminate the initial window and context
    if(!glMultiContext::getInstance().makeCurrent(_rc)){

        printf("failed to make current!!!");
    }
             // init engine here (GLEW was already initiated)
    engine = new Engine(800,600,1);

}
void GPUThread::Start(){



    printf("threaded view setup ok");

    ///init thread here :
    _thread=new boost::thread(boost::ref(*this));

    _thread->join();

}
void GPUThread::Stop(){
    // Signal the thread to stop (thread-safe)
    _mustStopMutex.lock();
    _mustStop=true;
    _mustStopMutex.unlock();

    // Wait for the thread to finish.
    if (_thread!=NULL) _thread->join();

}
// Thread function
void GPUThread::operator () ()
{
    bool mustStop;

    do
    {
        // Display the next animation frame
        DisplayNextFrame();
        _mustStopMutex.lock();
        mustStop=_mustStop;
        _mustStopMutex.unlock();
    }   while (mustStop==false);

}


void GPUThread::DisplayNextFrame()
{

    engine->Render(); //renders frame
    if(_frame == 101){
        _mustStop=true;
    }
}

GPUThread::~GPUThread(void)
{
    delete _view;
    if(_rc != 0)
    {
        glMultiContext::getInstance().deleteRenderingContext(_rc);
        _rc = 0;
    }
    if(_thread!=NULL)delete _thread;
}