Pick.cpp

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//------------------------------------------------------------------------
//C++ 
//                   ________    ____   ___ 
//                  |        \  /    | /  /
//                  +---+     \/     |/  /
//                  +--+|  |\    /|     < 
//                  |  ||  | \  / |  |\  \ 
//                  |      |  \/  |  | \  \ 
//                   \_____|      |__|  \__\
//                       Copyright  2003 
//                      Joe Michael Kniss
//               "All Your Base are Belong to Us"
//-------------------------------------------------------------------------

/// Pick.cpp

#include <GL/glew.h>
#include "Pick.h"
#include <algorithm>
#include <iostream>
#include <limits>

using namespace std;

////////////////////////////////////////////////////////////////
/// begin a pick, you need to call your draw loop and then
///   endPick when you are done.  
void Pick::startPickGL(double x, double y, double pickWin)
{
   GLint viewport[4];
   glGetIntegerv(GL_VIEWPORT,viewport);
   GLfloat proj[16];
   glGetFloatv(GL_PROJECTION_MATRIX,proj);

   /// set up projection matrix for picking
   glMatrixMode(GL_PROJECTION);
   {
      glPushMatrix();
      glLoadIdentity();
      gluPickMatrix(x, y, pickWin, pickWin, viewport);
      glMultMatrixf(proj);
   }
   glMatrixMode(GL_MODELVIEW);
   
   /// set up pick buffer and render mode
   glSelectBuffer(_pbSize, _pickBuffer);
   glRenderMode(GL_SELECT);

   /// initiallize name buffer
   glInitNames();

   _picking = true;
}

////////////////////////////////////////////////////////////////
/// for sorting our pick info's
struct PBSortZ1 {
   bool operator() (const PickInfo &pi1, const PickInfo &pi2)
   {
      return pi1.z1 < pi2.z1;
   }
};

////////////////////////////////////////////////////////////////
/// end a pick, fill the pick information vector
PickInfoVec Pick::endPickGL()
{
   /// catch the most obvious user mistake and report it
   ///   TODO: an assertion would force the user fix this too
   if(!_picking)
   {
      cerr << "Pick::endPickGL(), you must call startPickGL() before endPickGL()" << endl;
      return PickInfoVec();
   }
   _picking = false;

   /// reset projection matrix
   glMatrixMode(GL_PROJECTION);
   {  
      glPopMatrix();
   }
   glMatrixMode(GL_MODELVIEW);

   /// setting the render mode back returns hits 
   GLint hits = glRenderMode(GL_RENDER);

   /// see if we actually picked ANYTHING
   if(!hits) return PickInfoVec();

   /// we did so create the info vector
   PickInfoVec piv;

   /// loop over picks
   for(int i=0, j=0; i<hits; ++i)
   {
      ///////////////////
      /// make sure we don't overrun the pick buffer,
      ///  first check.
      if( j >= _pbSize )
      {
         cerr << "Pick::endPick(), pick-buffer overrun, try increasing the " 
            << "size of the pick buffer." << endl;
         sort(piv.begin(), piv.end(), PBSortZ1());
         return piv; ///< just return what we have
      }
      ///////////////////

      /// first item on stack is the number of names
      unsigned int nnames = _pickBuffer[j++];
      
      ///////////////////
      /// make sure we don't overrun the pick buffer
      ///   second check..
      if( int(j+nnames+1) >= _pbSize )
      {
         cerr << "Pick::endPick(), pick-buffer overrun, try increasing the " 
            << "size of the pick buffer.." << endl;
         sort(piv.begin(), piv.end(), PBSortZ1());
         return piv; ///< just return what we have
      }
      ///////////////////

      /// add the pick info to our vector
      piv.push_back(
         PickInfo(
           _pickBuffer[j  ]/double(std::numeric_limits<unsigned int>::max()), //z1
           _pickBuffer[j+1]/double(std::numeric_limits<unsigned int>::max()), //z2
           &(_pickBuffer[j+2]), nnames                                        //names
         )
      );

      /// increment j so we are at the right position in the pick buffer.
      j += nnames + 2;

   } /// end loop over picks

   /// sort pickInfo vector based on increasing z1 value
   sort(piv.begin(),piv.end(),PBSortZ1());  
   return piv;
}

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