蒙特卡诺近似与PBM

介绍蒙特卡诺近似的例子代码

#include<fstream> 
#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<string>
#include<ctime>
#include<memory>
using std::ifstream;
using std::ofstream;
using std::string;
using std::cout;
using std::endl;
using std::ios;
using std::unique_ptr;
double randx()
{
    return rand() % 100 / (double)99;
}

int main(void)
{
    ifstream ifs("D:/tex.pbm");
    string header;
    uint32_t w, h, l;
    ifs >> header;
    ifs >> w >> h >> l;
    cout << "w: " << w << " ,h: " << h << " ,l: " << l << endl;
    ifs.ignore();
    unsigned char* pixles = new unsigned char[w * h * 3];
    ifs.read((char*)pixles, w * h * 3);    

    int nsamples = 8;
    srand(time(0));
    float avgr = 0, avgg = 0, avgb = 0;
    float sumr = 0, sumg = 0, sumb = 0;
    for (int i = 0; i < nsamples; i++)
    {
        float x = randx() * w;
        float y = randx() * h;
        int n = ((int)(y * w) + int(x)) * 3;
        sumr += pixles[n];
        sumg += pixles[n + 1];
        sumb += pixles[n + 2];
    }
    sumr /= nsamples;
    sumg /= nsamples;
    sumb /= nsamples;
    for (int i = 0; i < h; i++)
    {
        for (int j = 0; j < w; j++)
        {
            int n = (i * w + j) * 3;
            avgr += pixles[n];
            avgg += pixles[n + 1];
            avgb += pixles[n + 2];
        }
    }
    avgr /= w * h;
    avgg /= w * h;
    avgb /= w * h;

    printf("Average: %0.2f %0.2f %0.2f \n", avgr, avgg, avgb);
    printf("Aproximation: %0.2f %0.2f %0.2f \n", sumr, sumg, sumb);
    delete pixles;

    system("pause");
    return 0;
}