我正在尝试设置并行多 GPU 屏幕外渲染上下文。我使用“OpenGL Insights”书，第 27 章，“NVIDIA Quadro 上的多 GPU 渲染”。我还查看了 wglCreateAffinityDCNV文档，但仍然无法确定。
我的机器有 2 个 NVidia Quadro 4000 卡（无 SLI）。在 Windows 7 64 位上运行。我的工作流程是这样的：
- 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（目前只尝试一个）
- 为每个上下文设置 boost 线程并使其在该线程中处于当前状态。
- 分别在每个线程上运行渲染程序。（不共享资源）
一切都是在没有错误的情况下创建并运行的，但是一旦我尝试从屏幕外 FBO 读取像素，我就会在这里得到一个空指针：
GLubyte* ptr = (GLubyte*)glMapBuffer(GL_PIXEL_PACK_BUFFER, GL_READ_ONLY);
glError 也返回“未知错误”
我认为可能是多线程是问题，但相同的设置在单线程上运行时会给出相同的结果。所以我相信它与上下文创作有关。
这是我的做法：
////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 :
..........
............
正如我所说，我在设备和上下文创建的任何阶段都没有出错。我究竟做错了什么 ？
更新：
好吧，似乎我发现了这个错误。我在调用 wglMakeCurrent() 之后调用了 glfwTerminate()，所以看起来最新的使“非当前”也成为新的上下文。虽然它是有线的，因为 OpenGL 命令不断执行。所以它在单个线程中工作。
但是现在，如果我使用 boost 踏板生成另一个线程，我会收到初始错误。这是我的线程类：
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;
}