From Fredric Mammond, fix for build using full extension checked mechansim

src/osg/BlendEquation.cpp

@@ -11,6 +11,11 @@
  * OpenSceneGraph Public License for more details.
 */
 #include <osg/BlendEquation>
+#include <osg/GLExtensions>
+#include <osg/State>
+#include <osg/Notify>
+#include <osg/buffered_value>
+
 
 using namespace osg;
 
@@ -28,8 +33,77 @@ BlendEquation::~BlendEquation()
 {
 }
 
-void BlendEquation::apply(State&) const
+void BlendEquation::apply(State& state) const
 {
-    glBlendEquation(_equation);
+
+   // get the contextID (user defined ID of 0 upwards) for the 
+    // current OpenGL context.
+    const unsigned int contextID = state.getContextID();
+    
+    const Extensions* extensions = getExtensions(contextID,true);
+                                        
+    if (!extensions->isBlendEquationSupported())
+    {
+        notify(WARN)<<"Warning: BlendEquation::apply(..) failed, BlendEquation is not support by OpenGL driver."<<std::endl;
+        return;
+    }
+
+    extensions->glBlendEquation(_equation);
+    
 }
 
+
+typedef buffered_value< ref_ptr<BlendEquation::Extensions> > BufferedExtensions;
+static BufferedExtensions s_extensions;
+
+BlendEquation::Extensions* BlendEquation::getExtensions(unsigned int contextID,bool createIfNotInitalized)
+{
+    if (!s_extensions[contextID] && createIfNotInitalized) s_extensions[contextID] = new Extensions;
+    return s_extensions[contextID].get();
+}
+
+void BlendEquation::setExtensions(unsigned int contextID,Extensions* extensions)
+{
+    s_extensions[contextID] = extensions;
+}
+
+
+BlendEquation::Extensions::Extensions()
+{
+    setupGLExtenions();
+}
+
+BlendEquation::Extensions::Extensions(const Extensions& rhs):
+    Referenced()
+{
+    _isBlendEquationSupported = rhs._isBlendEquationSupported;
+}
+
+void BlendEquation::Extensions::lowestCommonDenominator(const Extensions& rhs)
+{
+    if (!rhs._isBlendEquationSupported)  _isBlendEquationSupported = false;
+    if (!rhs._glBlendEquation)           _glBlendEquation = 0;
+}
+
+void BlendEquation::Extensions::setupGLExtenions()
+{
+    _isBlendEquationSupported = isGLExtensionSupported("GL_EXT_blend_equation") ||
+                             strncmp((const char*)glGetString(GL_VERSION),"1.2",3)>=0;
+
+    _glBlendEquation = getGLExtensionFuncPtr("glBlendEquation", "glBlendEquationEXT");
+}
+
+void BlendEquation::Extensions::glBlendEquation(GLenum mode) const
+{
+    if (_glBlendEquation)
+    {
+        typedef void (APIENTRY * GLBlendEquationProc) (GLenum mode);
+        ((GLBlendEquationProc)_glBlendEquation)(mode);
+    }
+    else
+    {
+        notify(WARN)<<"Error: glBlendEquation not supported by OpenGL driver"<<std::endl;
+    }
+}
+
+