text: #include "lodepng.h"
  #include <string>
  #include <vector>
  
  using namespace std;
  
  int main(int argc, char* argv[]) {
      string org(argv[1]);
      string trans(argv[2]);
      string out(argv[3]);
  
      vector<unsigned char> image_org;
      unsigned w1;
      unsigned h1;
      lodepng::decode(image_org, w1, h1, org);
  
      vector<unsigned char> image_trans;
      unsigned w2;
      unsigned h2;
      lodepng::decode(image_trans, w2, h2, trans);
  
      for (unsigned y = 0; y != h1; ++y) {
          for (unsigned x = 0; x != w1; ++x) {
              if (image_trans[4 * w1 * y + 4 * x + 3] != 0) {
                  image_org[4 * w1 * y + 4 * x + 0] = image_trans[4 * w1 * y + 4 * x + 0];
                  image_org[4 * w1 * y + 4 * x + 1] = image_trans[4 * w1 * y + 4 * x + 1];
                  image_org[4 * w1 * y + 4 * x + 2] = image_trans[4 * w1 * y + 4 * x + 2];
                  image_org[4 * w1 * y + 4 * x + 3] = image_trans[4 * w1 * y + 4 * x + 3];    
              }
          }
      }
  
      lodepng::encode(out, image_org, w1, h1);
  }