// ------------------------------------------------------------------------
  // This program is complementary material for the book:
  //
  // Frank Nielsen
  //
  // Visual Computing: Geometry, Graphics, and Vision
  //
  // ISBN: 1-58450-427-7
  //
  // Charles River Media, Inc.
  //
  //
  // All programs are available at www.charlesriver.com/visualcomputing/
  //
  // You may use this program for ACADEMIC and PERSONAL purposes ONLY. 
  //
  //
  // The use of this program in a commercial product requires EXPLICITLY
  // written permission from the author. The author is NOT responsible or 
  // liable for damage or loss that may be caused by the use of this program. 
  //
  // Copyright (c) 2005. Frank Nielsen. All rights reserved.
  // ------------------------------------------------------------------------
   
  // ------------------------------------------------------------------------
  // File: composite.cpp
  // 
  // Description: Simple image compositing demo
  // ------------------------------------------------------------------------
  
  include <stdafx.h>
  include <fstream>
  
  using namespace std;
  
  // Save a PPM Image
  void SaveImagePPM(unsigned char * data, int w, int h, char * file)
  {
          ofstream OUT(file, ios::binary);
          if (OUT){
      OUT << "P6" << endl << w << ' ' << h << endl << 255 << endl;
          OUT.write((char *)data, 3*w*h);
          OUT.close();}
  }
  
  // Load a PPM Image that does not contain comments.
  unsigned char * LoadImagePPM(char *ifile,  int &w, int &h)
  {
           char dummy1=0, dummy2=0; int maxc;
          unsigned char * img;
          ifstream IN(ifile, ios::binary);
  
          IN.get(dummy1);IN.get(dummy2);
          if ((dummy1!='P')&&(dummy2!='6')) {cerr<<"Not P6 PPM file"<<endl; return NULL;}
   
      IN >> w >> h;
      IN >> maxc;
      IN.get(dummy1);
          
      img=new  unsigned char[3*w*h];
          IN.read((char *)img, 3*w*h); 
          IN.close();
          return img;
  }
  
  int _tmain(int argc, _TCHAR* argv[])
  {
          char filebackground[]="background.ppm";
           char fileforeground[]="furrydog.ppm";
   char filematte[]="furrydog-matte.ppm";
          unsigned  char *imgout, * imgmatte, * imgback;
          int w,h;
          int i,j,index;
          double alpha;
  
          imgout=LoadImagePPM(fileforeground,w,h);
          imgmatte=LoadImagePPM(filematte,w,h);
          imgback=LoadImagePPM(filebackground,w,h);
  
          
  cout<<"Visual Computing: Geometry, Graphics, and Vision (ISBN:1-58450-427-7)"<<endl;
  cout<<"Demo program\n\n"<<endl;
  
  cout<<"Image compositing using alpha channel."<<endl;
  
          for(i=0;i<h;i++)
                  for(j=0;j<w;j++)
                  {
  index=3*(i*w+j);
  alpha=imgmatte[index]/255.0;
  
  imgout[index]=(unsigned char)((1-alpha)*imgback[index]+alpha*imgout[index]);
  imgout[index+1]=(unsigned char)((1-alpha)*imgback[index+1]+alpha*imgout[index+1]);
  imgout[index+2]=(unsigned char)((1-alpha)*imgback[index+2]+alpha*imgout[index+2]);
  
                  }
  
  SaveImagePPM(imgout,w,h,"composite.ppm");
  
  delete [] imgout;
  delete [] imgmatte;
  delete [] imgback;
  
  char line[256];
  cout<<"Press Return key"<<endl;
  gets(line);
          return 0;
  }