BachiLi

// smallgdpt: a simple implementation of gradient domain path tracing 
//                                       https://mediatech.aalto.fi/publications/graphics/GPT/ 
// adapted from smallpt by Kevin Beason http://www.kevinbeason.com/smallpt/
// and a screened poisson solver by Pravin Bhat http://grail.cs.washington.edu/projects/screenedPoissonEq/
// to build, type: g++ -o smallgdpt -fopenmp -O3 smallgdpt.cpp -L/usr/local/lib -lm -lfftw3
// you will need fftw3 http://www.fftw.org/ to compile
// usage: ./smallgdpt [number of samples per pixel]
#include <fftw3.h>
#include <math.h>   
#include <stdlib.h>