From Per Fahlberg, "Attached is a fix allowing removal of shaders from a program after it is

first compiled. It will also allow new shaders to be attached after the
program is first compiled."

include/osg/Program

@@ -203,6 +203,16 @@ class OSG_EXPORT Program : public osg::StateAttribute
                 inline GLint getUniformLocation( const std::string& name ) const { ActiveVarInfoMap::const_iterator itr = _uniformInfoMap.find(name); return (itr!=_uniformInfoMap.end()) ? itr->second._location : -1; }
                 inline GLint getAttribLocation( const std::string& name ) const { ActiveVarInfoMap::const_iterator itr = _attribInfoMap.find(name); return (itr!=_attribInfoMap.end()) ? itr->second._location : -1; }
 
+                inline void addShaderToAttach(Shader *shader)
+                {
+                    _shadersToAttach.push_back(shader);
+                }
+
+                inline void addShaderToDetach(Shader *shader)
+                {
+                    _shadersToDetach.push_back(shader);
+                }
+      
             protected:        /*methods*/
                 ~PerContextProgram();
 
@@ -225,6 +235,10 @@ class OSG_EXPORT Program : public osg::StateAttribute
                 typedef std::pair<const osg::Uniform*, unsigned int> UniformModifiedCountPair;
                 typedef std::vector<UniformModifiedCountPair> LastAppliedUniformList;
                 mutable LastAppliedUniformList _lastAppliedUniformList;
+      
+                typedef std::vector< ref_ptr<Shader> > ShaderList;
+                ShaderList _shadersToDetach;
+                ShaderList _shadersToAttach;
 
             private:
                 PerContextProgram();        // disallowed
@@ -247,7 +261,6 @@ class OSG_EXPORT Program : public osg::StateAttribute
         typedef std::vector< ref_ptr<Shader> > ShaderList;
         ShaderList _shaderList;
 
-
     private:
         Program& operator=(const Program&);        // disallowed
 };

include/osg/Shader

@@ -99,6 +99,9 @@ class OSG_EXPORT Shader : public osg::Object
         /** For a given GL context, attach a glShader to a glProgram */
         void attachShader(unsigned int contextID, GLuint program) const;
 
+        /** For a given GL context, detach a glShader to a glProgram */
+        void detachShader(unsigned int contextID, GLuint program) const;
+
         /** Query InfoLog from a glShader */
         bool getGlShaderInfoLog(unsigned int contextID, std::string& log) const;
 

src/osg/Program.cpp

@@ -2100,6 +2100,12 @@ bool Program::addShader( Shader* shader )
         if( shader == _shaderList[i].get() ) return false;
     }
 
+    // Add shader to PCPs
+    for( unsigned int cxt=0; cxt < _pcpList.size(); ++cxt )
+    {
+        if( _pcpList[cxt].valid() ) _pcpList[cxt]->addShaderToAttach( shader );
+    }
+
     shader->addProgramRef( this );
     _shaderList.push_back( shader );
     dirtyProgram();
@@ -2118,12 +2124,20 @@ bool Program::removeShader( Shader* shader )
     {
         if( shader == itr->get() )
         {
+            // Remove shader from PCPs
+            for( unsigned int cxt=0; cxt < _pcpList.size(); ++cxt )
+            {
+                if( _pcpList[cxt].valid() ) _pcpList[cxt]->addShaderToDetach( shader );
+            }
+
             shader->removeProgramRef( this );
             _shaderList.erase(itr);
+
             dirtyProgram();
             return true;
         }
     }
+
     return false;
 }
 
@@ -2196,9 +2210,10 @@ Program::PerContextProgram* Program::getPCP(unsigned int contextID) const
         // attach all PCSs to this new PCP
         for( unsigned int i=0; i < _shaderList.size(); ++i )
         {
-            _shaderList[i]->attachShader( contextID, _pcpList[contextID]->getHandle() );
+            _pcpList[contextID]->addShaderToAttach( _shaderList[i].get() );
         }
     }
+
     return _pcpList[contextID].get();
 }
 
@@ -2266,6 +2281,20 @@ void Program::PerContextProgram::linkProgram()
         << " contextID=" << _contextID
         <<  std::endl;
 
+    // Detach removed shaders
+    for( unsigned int i=0; i < _shadersToDetach.size(); ++i )
+    {
+        _shadersToDetach[i]->detachShader( _contextID, _glProgramHandle );
+    }
+    _shadersToDetach.clear();
+    
+    // Attach new shaders
+    for( unsigned int i=0; i < _shadersToAttach.size(); ++i )
+    {
+        _shadersToAttach[i]->attachShader( _contextID, _glProgramHandle );
+    }
+    _shadersToAttach.clear();
+
     _uniformInfoMap.clear();
     _attribInfoMap.clear();
     _lastAppliedUniformList.clear();

src/osg/Shader.cpp

@@ -240,6 +240,12 @@ void Shader::attachShader(unsigned int contextID, GLuint program) const
     if( pcs ) pcs->attachShader( program );
 }
 
+void Shader::detachShader(unsigned int contextID, GLuint program) const
+{
+    PerContextShader* pcs = getPCS( contextID );
+    if( pcs ) pcs->detachShader( program );
+}
+
 
 bool Shader::getGlShaderInfoLog(unsigned int contextID, std::string& log) const
 {