[菜鳥每天來段CUDA_C]CUDA與OpenGL互操作

本文要解決的問題是如何實現CUDA和OpenGL的互操作，使得GPU能夠將通用計算的運算結果交給OpenGL進行繪製。

本文的應用程序主要包括兩個方面：

1.      使用CUDA核函數生成圖像數據

2.      將數據傳遞給OpenGL驅動程序並進行渲染

實現這個功能需要按如下四個步驟：

Step1: 申明兩個全局變量，保存指向同一個緩衝區的不同句柄，指向要在OpenGL和CUDA之間共享的數據；

Step2: 選擇運行應用程序的CUDA設備(cudaChooseDevice),告訴cuda運行時使用哪個設備來執行CUDA和OpenGL (cudaGLSetGLDevice）；

Step3：在OpenGL中創建像素緩衝區對象；

Step4: 通知CUDA運行時將像素緩衝區對象bufferObj註冊爲圖形資源，實現緩衝區共享。

 

然後就可以按照一般的CUDA程序調用核函數進行計算。運行結果如下：

主要程序代碼如下：

/********************************************************************
*  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;
}

程序編譯的時候貌似要注意頭文件glut.h和glext.h的順序，否則會報錯~

 

參考資源：

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