text: /* OpenSceneGraph example, osgmotionblur.
  *
  *  Permission is hereby granted, free of charge, to any person obtaining a copy
  *  of this software and associated documentation files (the "Software"), to deal
  *  in the Software without restriction, including without limitation the rights
  *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  *  copies of the Software, and to permit persons to whom the Software is
  *  furnished to do so, subject to the following conditions:
  *
  *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  *  THE SOFTWARE.
  */
  
  
  #include <osgDB/ReadFile>
  #include <osgUtil/Optimizer>
  #include <osgViewer/Viewer>
  #include <iostream>
  
  class MotionBlurOperation: public osg::Operation
  {
  public:
      MotionBlurOperation(double persistence):
          osg::Operation("MotionBlur",true),
          cleared_(false),
          persistence_(persistence)
      {
      }
  
      virtual void operator () (osg::Object* object)
      {
          osg::GraphicsContext* gc = dynamic_cast<osg::GraphicsContext*>(object);
          if (!gc) return;
      
          double t = gc->getState()->getFrameStamp()->getSimulationTime();
  
          if (!cleared_)
          {
              // clear the accumulation buffer
              glClearColor(0, 0, 0, 0);
              glClear(GL_ACCUM_BUFFER_BIT);
              cleared_ = true;
              t0_ = t;
          }
  
          double dt = fabs(t - t0_);
          t0_ = t;
  
          // compute the blur factor
          double s = powf(0.2, dt / persistence_);
  
          // scale, accumulate and return
          glAccum(GL_MULT, s);
          glAccum(GL_ACCUM, 1 - s);
          glAccum(GL_RETURN, 1.0f);
      }
  
  private:
      bool cleared_;
      double t0_;
      double persistence_;
  };
  
  
  int main( int argc, char **argv )
  {
  
      // use an ArgumentParser object to manage the program arguments.
      osg::ArgumentParser arguments(&argc,argv);
      
      // set up the usage document, in case we need to print out how to use this program.
      arguments.getApplicationUsage()->setApplicationName(arguments.getApplicationName());
      arguments.getApplicationUsage()->setDescription(arguments.getApplicationName()+" is an OpenSceneGraph example that shows how to use the accumulation buffer to achieve a simple motion blur effect.");
      arguments.getApplicationUsage()->setCommandLineUsage(arguments.getApplicationName()+" [options] filename ...");
      arguments.getApplicationUsage()->addCommandLineOption("-h or --help","Display this information");
      arguments.getApplicationUsage()->addCommandLineOption("-P or --persistence","Set the motion blur persistence time");
      
  
      // construct the viewer.
      osgViewer::Viewer viewer;
  
      // if user request help write it out to cout.
      if (arguments.read("-h") || arguments.read("--help"))
      {
          arguments.getApplicationUsage()->write(std::cout);
          return 1;
      }
  
      double persistence = 0.25;
      arguments.read("-P", persistence) || arguments.read("--persistence", persistence);
  
      // read the scene from the list of file specified commandline args.
      osg::ref_ptr<osg::Node> loadedModel = osgDB::readNodeFiles(arguments);
      
      // if not loaded assume no arguments passed in, try use default mode instead.
      if (!loadedModel) loadedModel = osgDB::readNodeFile("cow.osg");
  
      // if no model has been successfully loaded report failure.
      if (!loadedModel) 
      {
          std::cout << arguments.getApplicationName() <<": No data loaded" << std::endl;
          return 1;
      }
  
  
      // set the display settings we can to request, OsgCameraGroup will read this.
      osg::DisplaySettings::instance()->setMinimumNumAccumBits(8,8,8,8);
  
      // pass the loaded scene graph to the viewer.
      viewer.setSceneData(loadedModel.get());
  
      // create the windows and run the threads.
      viewer.realize();
  
      osgViewer::Viewer::Windows windows;
      viewer.getWindows(windows);
      for(osgViewer::Viewer::Windows::iterator itr = windows.begin();
          itr != windows.end();
          ++itr)
      {
          (*itr)->add(new MotionBlurOperation(persistence));
      }
  
      return viewer.run();
  }
  