CUDA与OpenGL互操作实例

本文要解决的问题是如何实现CUDA和OpenGL的互操作，使得GPU能够将通用计算的运算结果交给OpenGL进行绘制。

本文的应用程序主要包括两个方面：

1.      使用CUDA核函数生成图像数据

2.      将数据传递给OpenGL驱动程序并进行渲染

实现这个功能需要按如下四个步骤：

Step1: 申明两个全局变量，保存指向同一个缓冲区的不同句柄，指向要在OpenGL和CUDA之间共享的数据；

Step2: 选择运行应用程序的CUDA设备(cudaChooseDevice),告诉cuda运行时使用哪个设备来执行CUDA和OpenGL (cudaGLSetGLDevice）；

Step3：在OpenGL中创建像素缓冲区对象；

Step4: 通知CUDA运行时将像素缓冲区对象bufferObj注册为图形资源，实现缓冲区共享。

然后就可以按照一般的CUDA程序调用核函数进行计算。运行结果如下：

/********************************************************************
*  SharedBuffer.cu
*  interact between CUDA and OpenGL
*********************************************************************/  

#include <stdio.h>
#include <stdlib.h>
#include "GL\glut.h"
#include "GL\glext.h"
#include <cuda_runtime.h>
#include <cutil_inline.h>
#include <cuda.h>
#include <cuda_gl_interop.h>  

#define GET_PROC_ADDRESS(str) wglGetProcAddress(str)
#define DIM 512  

PFNGLBINDBUFFERARBPROC    glBindBuffer     = NULL;
PFNGLDELETEBUFFERSARBPROC glDeleteBuffers  = NULL;
PFNGLGENBUFFERSARBPROC    glGenBuffers     = NULL;
PFNGLBUFFERDATAARBPROC    glBufferData     = NULL;  

// step one:
GLuint bufferObj;
cudaGraphicsResource *resource;  

__global__ void cudaGLKernel(uchar4 *ptr)
{
    int x = threadIdx.x + blockIdx.x * blockDim.x;
    int y = threadIdx.y + blockIdx.y * blockDim.y;
    int offset = x + y * blockDim.x * gridDim.x;  

    float fx = x/(float)DIM - 0.5f;
    float fy = y/(float)DIM - 0.5f;  

    unsigned char green = 128 + 127 * sin(abs(fx*100) - abs(fy*100));  

    ptr[offset].x = 0;
    ptr[offset].y = green;
    ptr[offset].z = 0;
    ptr[offset].w = 255;  

}  

 void drawFunc(void)
{
    glDrawPixels(DIM, DIM, GL_RGBA, GL_UNSIGNED_BYTE, 0);
    glutSwapBuffers();
}  

static void keyFunc(unsigned char key, int x, int y)
{
    switch(key){
        case 27:
            cutilSafeCall(cudaGraphicsUnregisterResource(resource));
            glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, 0);
            glDeleteBuffers(1, &bufferObj);
            exit(0);
    }
}  

int main(int argc, char* argv[])
{
    // step 2:
    cudaDeviceProp prop;
    int dev;  

    memset(&prop, 0, sizeof(cudaDeviceProp));
    prop.major = 1;
    prop.minor = 0;
    cutilSafeCall(cudaChooseDevice(&dev, &prop));
    cutilSafeCall(cudaGLSetGLDevice(dev));  

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowSize(DIM, DIM);
    glutCreateWindow("CUDA interact with OpenGL");  

    // step 3:
    glBindBuffer    = (PFNGLBINDBUFFERARBPROC)GET_PROC_ADDRESS("glBindBuffer");
    glDeleteBuffers = (PFNGLDELETEBUFFERSARBPROC)GET_PROC_ADDRESS("glDeleteBuffers");
    glGenBuffers    = (PFNGLGENBUFFERSARBPROC)GET_PROC_ADDRESS("glGenBuffers");
    glBufferData    = (PFNGLBUFFERDATAARBPROC)GET_PROC_ADDRESS("glBufferData");  

    glGenBuffers(1, &bufferObj);
    glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, bufferObj);
    glBufferData(GL_PIXEL_UNPACK_BUFFER_ARB, DIM*DIM*4, NULL, GL_DYNAMIC_DRAW_ARB);  

    // step 4:
    cutilSafeCall(cudaGraphicsGLRegisterBuffer(&resource, bufferObj, cudaGraphicsMapFlagsNone));  

    uchar4* devPtr;
    size_t size;
    cutilSafeCall(cudaGraphicsMapResources(1, &resource, NULL));
    cutilSafeCall(cudaGraphicsResourceGetMappedPointer((void**)&devPtr, &size, resource));  

    dim3 grids(DIM/16, DIM/16);
    dim3 threads(16, 16);
    cudaGLKernel<<<grids, threads>>>(devPtr);  

    cutilSafeCall(cudaGraphicsUnmapResources(1, &resource, NULL));
    glutKeyboardFunc(keyFunc);
    glutDisplayFunc(drawFunc);
    glutMainLoop();
    return 0;
}  

程序编译的时候貌似要注意头文件glut.h和glext.h的顺序，否则会报错~

参考资源：

1、Jason Sanders, Edward Kandrot, CUDA By Example: An Introduction toGeneral-Purpose GPU Programming (2011).

2、[菜鸟每天来段CUDA_C]CUDA与OpenGL互操作

3、CUDA与OpenGL交互开发

4、cuda与opengl互操作之PBO