From Julien Valentin, "To sum up changes, I had:

-some extensions in GLExtensions
  - GL_TEXTURE_BUFFER as target in osg::StateSet
  - a VBO based transform feed back example
"


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14651 16af8721-9629-0410-8352-f15c8da7e697

src/osg/Program.cpp

@@ -137,7 +137,7 @@ void Program::ProgramBinary::assign(unsigned int size, const unsigned char* data
 Program::Program() :
     _geometryVerticesOut(1), _geometryInputType(GL_TRIANGLES),
     _geometryOutputType(GL_TRIANGLE_STRIP),
-    _numGroupsX(0), _numGroupsY(0), _numGroupsZ(0)
+    _numGroupsX(0), _numGroupsY(0), _numGroupsZ(0), _feedbackmode(GL_SEPARATE_ATTRIBS)
 {
 }
 
@@ -180,6 +180,9 @@ Program::Program(const Program& rhs, const osg::CopyOp& copyop):
     _numGroupsX = rhs._numGroupsX;
     _numGroupsY = rhs._numGroupsY;
     _numGroupsZ = rhs._numGroupsZ;
+
+    _feedbackmode=rhs._feedbackmode;
+    _feedbackout=rhs._feedbackout;
 }
 
 
@@ -223,6 +226,9 @@ int Program::compare(const osg::StateAttribute& sa) const
     if( _numGroupsZ < rhs._numGroupsZ ) return -1;
     if( rhs._numGroupsZ < _numGroupsZ ) return 1;
 
+    if(_feedbackout<rhs._feedbackout) return -1;
+    if(_feedbackmode<rhs._feedbackmode) return -1;
+
     ShaderList::const_iterator litr=_shaderList.begin();
     ShaderList::const_iterator ritr=rhs._shaderList.begin();
     for(;
@@ -248,6 +254,24 @@ void Program::compileGLObjects( osg::State& state ) const
         _shaderList[i]->compileShader( state );
     }
 
+    if(!_feedbackout.empty())
+    {
+        const PerContextProgram* pcp = getPCP(contextID);
+        const GLExtensions* extensions = state.get<GLExtensions>();
+
+        unsigned int numfeedback = _feedbackout.size();
+        const char**varyings = new const char*[numfeedback];
+        const char **varyingsptr = varyings;
+        for(std::vector<std::string>::const_iterator it=_feedbackout.begin();
+            it!=_feedbackout.end();
+            it++)
+        {
+            *varyingsptr++=(*it).c_str();
+        }
+
+        extensions->glTransformFeedbackVaryings( pcp->getHandle(), numfeedback, varyings, _feedbackmode);
+        delete [] varyings;
+    }
     getPCP( contextID )->linkProgram(state);
 }
 
@@ -437,7 +461,7 @@ void Program::removeBindUniformBlock(const std::string& name)
 
 
 
-
+#include <iostream>
 void Program::apply( osg::State& state ) const
 {
     const unsigned int contextID = state.getContextID();