c++ - Julia 集的代码总是在 CUDA C 中生成灰度图像

Question

在在线资源的帮助下，我在 CUDA C/C++ 中编写了以下用于生成 Julia 集分形的代码。我已经尝试了几个小时，但我无法弄清楚为什么这总是生成一个灰色图像，而不是我在运行 CPU 代码时得到的图像。我是 CUDA C 和并行编程的新手，目前我指的是 CUDA by Example by Sanders and Kandrot .

这是代码的 CPU 变体，在 VS2013 中所有必要的导入都运行良好:

/*
 References:
 [1] http://stackoverflow.com/questions/23711681/generating-custom-color-palette-for-julia-set
 [2] http://www.cs.rit.edu/~ncs/color/t_convert.html
*/

#include <stdio.h>
#include <stdlib.h>
#include <complex>
#include <string.h>
#include <IL/il.h>
#include <IL/ilu.h>
#include <time.h>

using namespace std;

#define N 1024
#define SQRT_2 1.4142
#define MAX_ITER 512

void HSVtoRGB( float *r, float *g, float *b, float h, float s, float v );
void saveImage(int width, int height, unsigned char * bitmap, complex<float> seed);
void compute_julia(complex<float> c, unsigned char * image);


int main(int argc, char **argv)
{
    complex<float> c(0.285f, 0.01f);
    if(argc > 2)
    {
        c.real(atof(argv[1]));
        c.imag(atof(argv[2]));
    } else
        fprintf(stderr, "Usage: %s <real> <imag>\nWhere <real> and <imag> form the complex seed for the Julia set.\n", argv[0]);

    ilInit();
    unsigned char *image = new unsigned char[N*N*3]; //RGB image
    compute_julia(c, image);
    saveImage(N, N, image, c);
    delete[] image;
}

void compute_julia(complex<float> c, unsigned char * image)
{
    complex<float> z_old(0.0f, 0.0f);
    complex<float> z_new(0.0f, 0.0f);
    for(int y=0; y<N; y++)
        for(int x=0; x<N; x++)
        {
            z_new.real(4.0f * x / (N) - 2.0f);
            z_new.imag(4.0f * y / (N) - 2.0f);
            int i;
            for(i=0; i<MAX_ITER; i++)
            {
                z_old.real(z_new.real());
                z_old.imag(z_new.imag());
                z_new = pow(z_new, 2);
                z_new += c;
                if(norm(z_new) > 4.0f) break;
            }
            float brightness = (i<MAX_ITER) ? 1.0f : 0.0f;
            float hue = (i % MAX_ITER)/float(MAX_ITER - 1);
            hue = (120*sqrtf(hue) + 150);
            float r, g, b;
            HSVtoRGB(&r, &g, &b, hue, 1.0f, brightness);
            image[(x + y*N)*3 + 0] = (unsigned char)(b*255);
            image[(x + y*N)*3 + 1] = (unsigned char)(g*255);
            image[(x + y*N)*3 + 2] = (unsigned char)(r*255);
        }
}

void saveImage(int width, int height, unsigned char * bitmap, complex<float> seed)
{
    ILuint imageID = ilGenImage();
    ilBindImage(imageID);
    ilTexImage(width, height, 1, 3, IL_RGB, IL_UNSIGNED_BYTE, bitmap);
    //ilEnable(IL_FILE_OVERWRITE);
    char imageName[256];
    sprintf(imageName, "Julia %.3f + i%.3f.png", seed.real(), seed.imag());
    ilSave(IL_PNG, imageName);
    fprintf(stderr, "Image saved as: %s\n", imageName);
}

// r,g,b values are from 0 to 1
// h = [0,360], s = [0,1], v = [0,1]
//      if s == 0, then h = -1 (undefined)
void HSVtoRGB( float *r, float *g, float *b, float h, float s, float v )
{
    int i;
    float f, p, q, t;
    if( s == 0 ) {
        // achromatic (grey)
        *r = *g = *b = v;
        return;
    }
    h /= 60;            // sector 0 to 5
    i = floor( h );
    f = h - i;          // factorial part of h
    p = v * ( 1 - s );
    q = v * ( 1 - s * f );
    t = v * ( 1 - s * ( 1 - f ) );
    switch( i ) {
        case 0:
            *r = v;
            *g = t;
            *b = p;
            break;
        case 1:
            *r = q;
            *g = v;
            *b = p;
            break;
        case 2:
            *r = p;
            *g = v;
            *b = t;
            break;
        case 3:
            *r = p;
            *g = q;
            *b = v;
            break;
        case 4:
            *r = t;
            *g = p;
            *b = v;
            break;
        default:        // case 5:
            *r = v;
            *g = p;
            *b = q;
            break;
    }
}

这是相应的 GPU 版本(请注意，它目前还很不完善，一旦我能够从中获得基本功能，我就会这样做):

#include "cuda_runtime.h"
#include "device_launch_parameters.h"

#include <stdio.h>
#include <stdlib.h>
#include <complex>
#include <string.h>
#include <IL/il.h>
#include <IL/ilu.h>
#include <time.h>
/*
References:
[1] http://stackoverflow.com/questions/23711681/generating-custom-color-palette-for-julia-set
[2] http://www.cs.rit.edu/~ncs/color/t_convert.html
*/

using namespace std;

#define N 1024
#define SQRT_2 1.4142
#define MAX_ITER 512

struct cuComplex {
    float r;
    float i;
    __host__ __device__ cuComplex(float a, float b) : r(a), i(b) {}
    __host__ __device__ float magnitude2(void) {
        return r * r + i * i;
    }
    __host__ __device__ cuComplex operator*(const cuComplex& a) {
        return cuComplex(r*a.r - i*a.i, i*a.r + r*a.i);
    }
    __host__ __device__ cuComplex operator+(const cuComplex& a) {
        return cuComplex(r + a.r, i + a.i);
    }
};

void HSVtoRGB(float *r, float *g, float *b, float h, float s, float v);
void saveImage(int width, int height, unsigned char * bitmap, cuComplex seed);
void compute_julia(complex<float> c, unsigned char * image);
__global__ void compute_julia_gpu(unsigned char* image);
__device__ void HSVtoRGB_GPU(float *r, float *g, float *b, float h, float s, float v);

int main(int argc, char **argv)
{
    cuComplex c(-0.8f, 0.156f);
    /*
    if (argc > 2)
    {
        c.real(atof(argv[1]));
        c.imag(atof(argv[2]));
    }*/
    fprintf(stderr, "Usage: %s <real> <imag>\nWhere <real> and <imag> form the complex seed for the Julia set.\n", argv[0]);

    ilInit();

    dim3 grid(N, N);
    unsigned char *image = new unsigned char[N*N * 3]; //RGB image

    size_t size = sizeof(image);

    unsigned char *d_image; //RGB image

    cudaMalloc((void **)&d_image, size);

    compute_julia_gpu<<<grid, 1>>>(d_image);

    cudaMemcpy(image, d_image, size, cudaMemcpyDeviceToHost);

    saveImage(N, N, image, c);

    cudaFree(d_image);
    delete[] image;
}

__global__ void compute_julia_gpu(unsigned char* image) {
    /*
    complex<float> z_old(0.0f, 0.0f);
    complex<float> z_new(0.0f, 0.0f);
    complex<float> c(-0.8f, 0.156f);
    */
    cuComplex z_old(0.0, 0.0);
    cuComplex z_new(0.0, 0.0);
    cuComplex c(-0.8f, 0.156f);
    int x = blockIdx.x;
    int y = blockIdx.y;
    z_new.r = (4.0f * x / (N)-2.0f);
    z_new.i = (4.0f * y / (N)-2.0f);
    int i = 0;
    for (i = 0; i<MAX_ITER; i++)
    {
        z_old.r = z_new.r;
        z_old.i = z_new.i;
        z_new = (z_new * z_new) + c;
        if (z_new.magnitude2() > 4.0f) break;
    }
    float brightness = (i<MAX_ITER) ? 1.0f : 0.0f;
    float hue = (i % MAX_ITER) / float(MAX_ITER - 1);
    hue = (120 * sqrtf(hue) + 150);
    float r, g, b;
    HSVtoRGB_GPU(&r, &g, &b, hue, 1.0f, brightness);
    image[(x + y*N) * 3 + 0] = (unsigned char)(b * 255);
    image[(x + y*N) * 3 + 1] = (unsigned char)(g * 255);
    image[(x + y*N) * 3 + 2] = (unsigned char)(r * 255);
}

void saveImage(int width, int height, unsigned char * bitmap, cuComplex seed)
{
    ILuint imageID = ilGenImage();
    ilBindImage(imageID);
    ilTexImage(width, height, 1, 3, IL_RGB, IL_UNSIGNED_BYTE, bitmap);
    //ilEnable(IL_FILE_OVERWRITE);
    char imageName[256];
    sprintf(imageName, "Julia %.3f + i%.3f.png", seed.r, seed.i);
    ilSave(IL_PNG, imageName);
    fprintf(stderr, "Image saved as: %s\n", imageName);
}

__device__ void HSVtoRGB_GPU(float *r, float *g, float *b, float h, float s, float v)
{
    int i;
    float f, p, q, t;
    if (s == 0) {
        // achromatic (grey)
        *r = *g = *b = v;
        return;
    }
    h /= 60;            // sector 0 to 5
    i = floor(h);
    f = h - i;          // factorial part of h
    p = v * (1 - s);
    q = v * (1 - s * f);
    t = v * (1 - s * (1 - f));
    switch (i) {
    case 0:
        *r = v;
        *g = t;
        *b = p;
        break;
    case 1:
        *r = q;
        *g = v;
        *b = p;
        break;
    case 2:
        *r = p;
        *g = v;
        *b = t;
        break;
    case 3:
        *r = p;
        *g = q;
        *b = v;
        break;
    case 4:
        *r = t;
        *g = p;
        *b = v;
        break;
    default:        // case 5:
        *r = v;
        *g = p;
        *b = q;
        break;
    }
}

感谢任何帮助，谢谢。

Answer 1

问题是你的大小变量:

#include <iostream>
#include <string.h>
using namespace std;

#define N 1024

int main() {
    unsigned char *image = new unsigned char[N*N * 3]; //RGB image
    size_t size = sizeof(image);
    cout << size;
    return 0;
}

在这种情况下，输出为 4(在 32 位架构上)，因为 sizeof 返回变量类型的大小。在这种情况下，它是 unsigned char * 并且是 4 字节 长。

您可以运行 cuda-memcheck ./yourExecuteable，当您的代码对 GPU 的全局内存执行越界访问时，您将看到错误。您会看到很多错误，因为您只为 d_image 数组分配了 4 个字节的全局内存。