CUDA OpenGL互操作，资源映射混乱缓冲区。

Question

我最近开始编写CUDA OpenGL互操作代码。大部分时间我在Linux环境下开发。当我尝试将我的代码转移到运行OS X的MacBook Pro上时，我遇到了以下问题：

每当我将OpenGL的顶点缓冲区作为资源映射到CUDA时，它会破坏存储在相应缓冲区中的数据。

这是我的代码:

// OpenGL and window handler includes
#include <GL/glew.h>
#include <SDL/SDL.h>
#include <OpenGL/GL.h>

// OpenGL/CUDA interop
#include <cuda_runtime.h>
#include <cuda_gl_interop.h>

// C libraries
#include <iostream>

int main(int argc, char* argv[])
{
    GLuint vbo;
    struct cudaGraphicsResource *cuda_vbo_resource;

    // create OpenGL context with SDL
    SDL_Init(SDL_INIT_VIDEO);
    SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
    SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
    SDL_SetVideoMode( 400, 200, 16, SDL_OPENGL);

    // initialize extension wrangler
    glewInit();

    // set cuda/GL device
    cudaGLSetGLDevice(0);

    // generate buffer
    glGenBuffers(1, &vbo);

    // fill buffer with data (1, 2, 3)
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    int inData[] = {1,2,3};
    glBufferData(GL_ARRAY_BUFFER, 3*sizeof(int), inData, GL_DYNAMIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    // Register buffer with cuda
    cudaGraphicsGLRegisterBuffer(&cuda_vbo_resource, vbo,             
                                        cudaGraphicsMapFlagsWriteDiscard);

    // let's have a look at the buffer
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    int* mappedBuffer = (int *) glMapBuffer(GL_ARRAY_BUFFER,GL_READ_ONLY);
    printf("\tbefore mapping: %d, %d, %d\n",mappedBuffer[0], mappedBuffer[1], 
            mappedBuffer[2]);
    glUnmapBuffer(GL_ARRAY_BUFFER);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    // map and unmap the cuda resource
    if (cudaGraphicsMapResources(1, &cuda_vbo_resource, 0) != cudaSuccess)
        printf("Resource mapping failed...\n");
    if (cudaGraphicsUnmapResources(1, &cuda_vbo_resource, 0) != cudaSuccess)
        printf("Resource unmapping failed...\n");

    // let's have a look at the buffer again
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    mappedBuffer = (int *) glMapBuffer(GL_ARRAY_BUFFER,GL_READ_ONLY);
    printf("\tafter mapping: %d, %d, %d\n",mappedBuffer[0], mappedBuffer[1], 
            mappedBuffer[2]);
    glUnmapBuffer(GL_ARRAY_BUFFER);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    // unregister the cuda resource
    cudaGraphicsUnregisterResource(cuda_vbo_resource);

    // delete the buffer
    glBindBuffer(1, vbo);
    glDeleteBuffers(1, &vbo);

    return 0;
}

编译后执行以下命令：

g++ -o resourceMapping resourceMapping.cpp `sdl-config --cflags --libs` -lglew 
         -framework OpenGL -I /usr/local/cuda/include  -L /usr/local/cuda/lib -lcudart

我明白了。

before mapping: 1, 2, 3
after mapping:  0, 33554432, 32

有人知道为什么映射会更改缓冲区数据吗？这对我来说特别令人困惑，因为在Linux机器上不会发生这种情况。

感谢任何评论或提示！

- nils

Answer 1

我注意到您使用cudaGraphicsMapFlagsWriteDiscard注册了vbo。

从这里得知，"指定CUDA不会从此资源中读取，并将覆盖资源的所有内容，因此之前存储在资源中的数据都不会被保留。"

也许尝试使用cudaGraphicsMapFlagsNone或cudaGraphicsMapFlagsReadOnly？

- Roger Allen